Is a Catalyst Always Needed? The Case of the Knoevenagel Reaction with Malononitrile

The aim of this Perspective is to start a discussion about the real usefulness of more or less sophisticated catalytic systems for the Knoevenagel reaction with malononitrile, a reaction that can take place under mild conditions without the need of a catalyst. From a sustainable viewpoint the questions are: Is it useful to increase the rate of a reaction that already occurs under mild conditions? Is it useful to spend resources and time in designing, characterizing and realizing complex catalytic systems for such reaction? Does it make sense to carry out the reaction under conditions such as to have a slower reaction rate and therefore to find a catalyst that is able to increase it?

ChemInform Abstract: Hydrophobically Directed Aldol Reactions: Polystyrene-Supported L-Proline as a Recyclable Catalyst for Direct Asymmetric Aldol Reactions in the Presence of Water.

A simple synthetic methodology for the preparation of a polystyrene-supported L-proline material is reported, and this material has been used as catalyst in direct asymmetric aldol reactions between several ketones and arylaldehydes to furnish aldol products in high yields and stereoselectivities. Screening of solvents showed that these reactions take place only in the presence of water or methanol, at lower levels of conversion in the latter case. This solvent effect, coupled with the observed high stereoselectivities, has been explained in terms of the formation of a hydrophobic core in the inner surface of the resin, whereas the hydrophilic proline moiety lies at the resin/water interfac…

L-prolinammide supportata su polistirene come organocatalizzatore altamente enantioselettivo nella reazione aldolica diretta

SBA-15/POSS-Imidazolium Hybrid as Catalytic Nanoreactor

Supported imidazolium modified polyhedral oligomeric silsesquioxanes (POSS) on SBA-15 have been used as platform for Pd(II) species. The so-obtained material was firstly characterized by means of TGA, solid state NMR, TEM, XPS, SAXS, porosimetry and ICP-OES and it was successfully tested as pre-catalyst in C−C cross couplings, namely Suzuki-Miyaura and Heck reactions. In both cases, the solid proved to be highly efficient and easily recoverable from the reaction mixture. The recyclability was verified for up to seven cycles without showing any activity decrease. Interestingly, only Pd(II) was detected in the reused catalyst in the Heck reaction. Therefore, the versatility of the material w…

Host—Guest Interactions Involving Cyclodextrins: Useful Complementary Insights Achieved by Polarimetry.

Abstract By means of simple polarimetry, we studied the binding abilities of native α-, β-, and γ-cyclodextrins toward a group of suitably chosen model guests. We were able to get reliable estimations of the binding constants K, spread over a wide range (from 3.7 to 12,300 M−1), allowing us to carry on interesting comparisons. A comprehensive discussion of polarimetric data, and in particular a detailed analysis of the variations ΔΘ of molar optical activities consequent to inclusion, offered us the opportunity to get useful insights into the structure and dynamic behavior of host–guest complexes.

Sintesi e studio fotofisico di sistemi Eu@POSS: controllo dell’emissione attraverso isomeria cis-trans.

Light-induced trans-cis isomerization of terpyridine functionalized POSS nanostructures self-assembled in presence of Eu3+ ions

A joint experimental and ab initio study on the reactivity of several hydroxy selenides. Stereoselective synthesis of cis-disubstituted tetrahydrofurans via seleniranium ions

Abstract The reactivity of several hydroxy selenides bearing an ethereal chain with catalytic amounts of perchloric acid in dichloromethane was investigated. Results showed that the position of the oxygen atom with respect to the seleniranium ring was crucial in order to get a good yield of the cyclized product. The factors on which yields of the 5- endo cyclization of the seleniranium ions depend were analysed by ab initio (HF/3-21G ∗ ) studies. An explanation of the different coordinating ability, towards the positively charged selenium atom, of the allylic OMe and homoallylic OH-2 groups was given.

Low-loading asymmetric organocatalysis

Asymmetric organocatalysis is now recognized as the third pillar of asymmetric synthesis. Recent years have witnessed increasing interest towards the use of highly active and stereoselective organocatalysts. This critical review documents the advances in the development of chiral organocatalysts which are systematically used in ≤3 mol% loading in all the sub-areas of the field, namely aminocatalysis, Brønsted acids and bases, Lewis acids and bases, hydrogen bond-mediated catalysis, phase transfer and N-heterocyclic carbene catalyses (194 references).

Novel Hydroxyproline-derivatives as powerful aldolase-I mimics

MICROWAVE-ASSISTED FUNCTIONALIZATION OF HALLOYSITE NANOTUBE SURFACE

Halloysite, Al2Si2O5·2H2O, is a naturally occurring two-layered alluminosilicate, chemically similar to kaolin, which has a predominantly high-aspect-ratio hollow tubular structure in the submicrometer range and an internal diameter in the nanometer range. The size of halloysite nanotubes (HNTs), generally varies from 50 to 70 nm in external diameter, ca. 15 nm diameter lumen, and 0.5 to 1 μm in length. Halloysite tubes have aluminol (Al-OH) groups on the internal surface and siloxan groups (Si-O-Si) on the external surface. The very large diameter of the halloysite lumen makes it potentially suitable for the accommodation of a range of guests. In recent reports, for example, the mesoporous…

Recyclable Organocatalysts in Asymmetric Reactions

An E-Factor Minimized Protocol for a Sustainable and Efficient Heck Reaction in Flow

A highly sustainable and waste-minimized protocol for Heck coupling has been defined. Optimal conditions have been defined by exploiting a heterogeneous catalyst based on supported ionic liquid-like phases featuring high Pd loading (10 wt %) and by optimizing its efficiency in a recoverable green reaction medium (acetonitrile/water azeotrope). Pure products 4a–l and 6a–h have been isolated chromatography-free in high yields (74–99%) and with extremely low environmental factor (E-factor) values (2.3–5.0). With the application of flow technology, the selected heterogeneous base and Pd catalyst have been fully recovered and reused, and minimum palladium leaching allowed for isolation of the fi…

Diastereoselective synthesis of substituted 2-phenyltetrahydropyrans as useful precursors of aryl C-glycosides via selenoetherification

The cyclization of several substituted 5-phenyl-pent-4-en-1-ols with selenium electrophiles along some mechanistic considerations is discussed. In particular, an efficient diastereoselective synthesis of a 2,3,5,6-tetrasubstitued tetrahydropyran is reported. These findings open an interesting approach: the use of chiral selenium electrophiles for cyclization of chiral substrates. The cyclized products are useful starting material for the synthesis of D- or L-aryl C-glycosides.

Lipase-catalyzed resolution of anti-6-substituted 1,3-dioxepan-5-ols

Abstract Several anti-6-substituted 1,3-dioxepan-5-ols were kinetically resolved using an immobilized lipase (Amano PS–C II) in toluene in the presence of vinyl acetate at 30 °C. This approach provided, in some cases, the alcohol and the acetate in high enantiomeric purity, depending on the nature of the substituent (R = N3, SePh, I, OBn) and the acetal group (unsubstituted or dimethyl). The role of the size of substituents is also discussed. Enantiopure anti-6-substituted 1,3-dioxepan-5-ols are useful building blocks.

Green conditions for the Suzuki reaction using microwave irradiation and a new HNT- supported ionic liquid-like phase (HNT-SILLP) catalyst

A new catalytic system based on modified halloysite nanotubes was employed in the Suzuki reaction under microwave irradi- ation. A set of solvents, times and bases was screened and the best experimental conditions were obtained when the reactions were carried out for 10 min in water–ethanol at 120 °C in presence of K2CO3 as base. Good recyclability was observed. The new catalytic system was employed using either 1 mol% or 0.1 mol%. The palladium catalyst displayed good activity, allowing the synthesis of several biphenyl compounds in high yield working with only 0.1 mol% palladium loading. The application of mi- crowave irradiation decreased the reaction time and also improved conversion wi…

Materiali ibridi a base di POSS-Imidazolio per la conversione della CO2 in carbonati ciclici

Lo sviluppo di catalizzatori per i processi di conversione della CO2 è una tematica che sta rivestendo un ruolo di rilevante importanza in ambito non soltanto accademico ma anche industriale grazie alla possibilità di trasformare un rifiuto, quale il diossido di carbonio, in una vasta gamma di prodotti. Nel presente lavoro, nuovi materiali ibridi costituiti da silsesquiossani poliedrici oligomerici (POSS) supportati su silice e funzionalizzati con sali di imidazolio sono stati progettati per la fissazione della CO2. 1 Tutti i solidi sono stati ampiamente caratterizzati e testati per la sintesi di carbonati ciclici tramite reazione tra CO2 ed epossidi in condizioni di reazione solvent-free (…

Bisoxazoline-Fullerene Hybrid Systems for Asymmetric Catalysis

Supported ionic liquid asymmetric cathalysis. A new method for chiral catalyst recycling

A new method for chiral catalysts recycling, based on the supported ionic liquid asymmetric catalysis concept, has been developed. This concept involves the treatment of a monolayer of covalently attached ionic liquid on the surface of silica gel with additional ionic liquid. These layers serve as the reaction phase in which the homogeneous chiral catalyst is dissolved. As first application of this concept the L-proline-catalyzed aldol reaction has been carried out. Good yields and ee values, comparable with those obtained under homogeneous conditions have been obtained. Moreover, this material shows high regenerability.

ChemInform Abstract: Substituent Effect on Oxidative Cyclization of Aldehyde Thiosemicarbazones with Ferric Chloride.

The reactivity of aldehyde thiosemicarbazones 1 with ferric chloride solutions was examined. When compounds 1 are not substituted on the N-2 nitrogen atom formation of 1,3,4-thiadiazole 3 heterocyclic ring was observed. In contrast 1,2,4-triazoline 4 and/or 1,3,4-thiadiazoline 5 heterocyclic rings were afforded when N-2 nitrogen atom carried a methyl or a phenyl group. The reaction mechanism is also discussed.

Recyclable Chiral Imidazolidinone Catalyst for α-Alkylation of Aldehydes

Design of POSS-Imidazolium Supported Hybrids for the Conversion of Carbon Dioxide into Cyclic Carbonates

Nowadays, the design of heterogeneous catalysts for the conversion of CO2 into useful chemical products is attracting the attention of the scientific community. The catalytic processes involving carbon dioxide as C1 feedstock are of growing interest for the sustainable development.1 The synthesis of cyclic carbonates by coupling CO2 with epoxides is one of the most interesting pathways for the conversion of carbon dioxide in terms of both atom economy and final products applications. Moreover, ionic liquids emerged as one of the most active catalysts for the production of cyclic carbonates starting from CO2 and epoxides.2 Herein, a series of heterogeneous catalytic systems bearing imidazoli…

Binding properties of mono-(6-deoxy-6-amino)-β-cyclodextrin towards p-nitroaniline derivatives: a polarimetric study

Abstract Polarimetry was used in order to investigate the formation of supramolecular complexes between mono-6-amino-β-cyclodextrin and various p-nitroaniline derivatives at two different pH values. Comparison with the behaviour of native β-cyclodextrin gave us the opportunity to consider the effect exerted by the presence of charged groups, having different solvation requirements, on the binding equilibrium. Data offer some support to the hypothesis of ‘dynamic co-inclusion’ of solvent molecules within the host–guest complex.

ChemInform Abstract: New Ionic Liquid-Modified Silica Gels as Recyclable Materials for L-Proline- or H-Pro-Pro-Asp-NH2-Catalyzed Aldol Reaction.

L-proline and the tripeptide H–Pro–Pro–Asp–NH2 (1) have been supported, by adsorption, onto the surface of modified silica gels functionalized with a monolayer of covalently attached 1,2-dimethyl-imidazolium chloride, tetrafluoroborate or hexafluorophosphate ionic moieties, respectively. Three different linkers were used to attach the ionic liquid moiety to the surface of these supports. The resulting materials have been used as catalysts for the aldol reaction between acetone and several substituted benzaldehydes. Good yields and enantioselectivities, comparable to or better than those obtained under homogeneous conditions, were obtained. These materials are easily recovered by filtration,…

ChemInform Abstract: Green Conditions for the Suzuki Reaction Using Microwave Irradiation and a New HNT-Supported Ionic Liquid-Like Phase (HNT-SILLP) Catalyst.

Aryl iodides are coupled with conversions comparable to aryl bromides whereas conversions of aryl chlorides are significantly lower.

Thiazolium salts as catalysts for etherification reaction

ChemInform Abstract: Palladium Supported on Cross-Linked Imidazolium Network on Silica as Highly Sustainable Catalysts for the Suzuki Reaction under Flow Conditions.

3-Mercaptopropyl-modified silica-supported bis-imidazolium Pd-catalysts are developed and successfully utilized for Suzuki reactions.

Modified Nanocarbons for Catalysis

Nanocarbons represent useful scaffolds in the preparation of last generation nanostructured catalysts, and their chemical functionalization through covalent or non-covalent modification is becoming an important tool for introducing well-distributed anchoring points and, in the meantime, could be the first step toward the assembling of hybrid nanostructured materials with a hierarchical order. In this Review are reported synthesis and catalytic applications of chemically modified nanocarbons such as fullerene, carbon nanotubes, graphene, nanohorns and nanodiamonds in organocatalytic and metal-based (metal nanoparticles, organometallic complexes) reactions, covering major chemical reactions e…

Stereoselective aldol reaction catalyzed by a highly recyclable polystyrene supported substituted prolinamide catalyst

Polystyrene supported substituted prolinamide was used as catalyst in the aldol reaction between cyclohexanone or acetone and several substituted benzaldehydes in chloroform/water. This catalyst afforded aldol products in high yields and stereoselectivities, especially in the case of reactions performed with acetone. The catalyst was easily recovered by filtration and reused, after regeneration with formic acid, up to 22 times.

Prolinamide-Supported Polystyrene: a Novel Highly Recyclable Organocatalyst for the Asymmetric Aldol Reaction

Multilayered supported ionic liquids as catalysts for chemical fixation of carbon dioxide

Multilayered, covalently supported ionic liquid phase (mlc-SILP) materials were synthesized by using a new approach based on the grafting of bis-vinylimidazolium salts on different types of silica or polymeric supports. The obtained materials were characterized and tested as catalysts in the reaction of supercritical carbon dioxide with various epoxides to produce cyclic carbonates. The material prepared by supporting a bromide bis-imidazolium salt on the ordered mesoporous silica SBA-15 was identified as the most active catalyst for the synthesis of cyclic carbonates and displayed improved productivity compared with known supported ionic liquid catalysts. The catalyst retained its high act…

ChemInform Abstract: Asymmetric Synthesis Using Polymer-Immobilized Proline Derivatives

L-prolina supportata su polistirene: un versatile organocatalizzatore eterogeneo

Supported Organocatalysts: a Powerful Tool in Organic Synthesis

Supported Ionic Liquid Asymmetric Catalysis. A New Method for Chiral Catalysts Recycling. The Case of Proline-Catalyzed Aldol Reaction.

A new method for chiral catalysts recycling, based on the supported ionic liquid asymmetric catalysis concept, has been developed. This concept involves the treatment of a monolayer of covalently attached ionic liquid on the surface of silica gel with additional ionic liquid. These layers serve as the reaction phase in which the homogeneous chiral catalyst is dissolved. As first application of this concept the L-proline-catalyzed aldol reaction has been carried out. Good yields and ee values, comparable with those obtained under homogeneous conditions have been obtained. Moreover, this material shows high regenerability.

Hydrophobically directed aldol reactions: polystyrene-supported L-proline as a recyclable catalyst for direct asymmetric aldol reactions in the presence of water

A simple synthetic methodology for the preparation of a polystyrene- supported L-proline material is reported, and this material has been used as catalyst in direct asymmetric aldol reactions between several ketones and arylaldehydes to furnish aldol products in high yields and stereoselectivities. Screening of solvents showed that these reactions take place only in the presence of water or methanol, at lower levels of conversion in the latter case. This solvent effect, coupled with the observed high stereoselectivities, has been ex- Introduction In the last decade organocatalysis has became a field of great interest.[1] Organocatalysts are metal-free small organic molecules that are able t…

Oxidative degradation properties of Co-based catalysts in presence of ozone

Cover Feature: Tuneable Emission of Polyhedral Oligomeric Silsesquioxane Based Nanostructures that Self‐Assemble in the Presence of Europium(III) Ions: Reversible trans ‐to‐ cis Isomerization (ChemPlusChem 3/2020)

A study on the stability of carbon nanoforms–polyimidazolium network hybrids in the conversion of co2 into cyclic carbonates

Three different carbon nanoforms (CNFs), single-walled and multi-walled carbon nanotubes (SWCNTs, MWCNTs) and carbon nanohorns (CNHs), have been used as supports for the direct polymerization of variable amounts of a bis-vinylimidazolium salt. Transmission electron microscopy confirmed that all CNFs act as templates on the growth of the polymeric network, which perfectly covers the nanocarbons forming a cylindrical (SWCNTs, MWCNTs) or spherical (CNHs) coating. The stability of these hybrid materials was investigated in the conversion of CO2 into cyclic carbonate under high temperature and CO2 pressure. Compared with the homopolymerized monomer, nanotube-based materials display an improved c…

A quantitative study of substituent effects on oxidative cyclization of some 2-methylsubstituted aldehydes. Thiosemicarbazones induced by ferric chloride

In order to gain further mechanistical information about the cyclization of thiosemicarbazones and thiosemicarbazone-type substrates induced by metallic salts as oxidizing agents, we performed the synthesis of substrates 1a-s and a kinetic study of the oxidative cyclization of 1 to 5-imino-Δ2-1,3,4-thiadiazole 2 and 1,2,4-triazoline-5-thione 3 derivatives induced by methanolic ferric chloride solutions. The results of cyclization were compared to those of corresponding semicarbazones. The kinetic data were analyzed by means of the Hammett's equation and ρ values discussed.

A competitive reactivity study on the oxidative cyclization of thiosemicarbazones into 1,3,4-thiadiazoles

Abstract In order to obtain useful insights on the mechanism of formation of 2(3H)-imino-1,3,4-thiadiazoles by oxidative cyclization of aldehyde thiosemicarbazones with Cu(II) or Fe(III) salts, a competitive reactivity study was performed on a suitable set of diversely substituted substrates, by means of HPLC techniques. This approach enabled to exploit Hammett’s equation without performing otherwise difficult-to-run kinetic experiments. The results presented herein support the hypothesis that the formation of the thiadiazole ring is induced by the attack of the oxidizing Lewis acid metal cation onto the imine-like nitrogen atom of the thiosemicarbazone substrate. Beyond mechanistic interpr…

Asymmetric Aldol Reaction with Polystyrene-Supported Proline-Based Catalysts

Nuovi ibridi [60]fullerene-liquido ionico

White light emitting silsesquioxane based materials: the importance of a ligand with rigid and directional arms

The synthesis of a novel polyhedral oligomeric silsesquioxane functionalized with eight rigid and directional terpyridine-based arms (Ter-POSS) was successfully achieved via a Sonogashira reaction. The POSS based ligand was extensively characterized using different techniques including 1H, 13C and 29Si NMR as well as UV-Vis and fluorescence spectroscopies. The assembly of these nano-caged units in the presence of different transition metal ions (Fe2+, Zn2+ and Cu2+) as well as of a cation from the lanthanides (Eu3+) was investigated using absorption and emission spectroscopies. The final materials display an evident emission in different regions of the visible spectrum as a function of the …

Palladium Supported on Cross-Linked Imidazolium Network on Silica as Highly Sustainable Catalysts for the Suzuki Reaction under Flow Conditions

Highly cross-linked imidazolium-based materials, obtained by radical oligomerization of bis-vinylimidazolium salts in the presence of 3-mercaptopropyl-modified silica gel, were used as supports for palladium catalysts. Thanks to the high imidazolium loading these materials were able to support a high amount of the metal (10 wt%). Such materials were characterized by several techniques (13C magic angle spinning nuclear magnetic resonance, the Brunauer-Emmett-Teller technique, X-ray photoelectron spectroscopy, and transmission electron microscopy). The palladium catalysts displayed good activity allowing the synthesis of several biphenyl compounds in high yields working with only 0.1 mol% of …

L-Prolina supportata su polistirene: un versatile catalizzatore eterogeneo

Cross-Linked Polyamine from Imidazolium-Based Materials: A Simple Route to Useful Catalytic Materials

Cross-linked polyamine-based materials were easily prepared by reduction of the corresponding cross-linked imidazolium-based materials with sodium borohydride in hot ethanol. Overall, the synthetic procedure is based on the polymerization of a suitable bis-vinylimidazolium salt with or without a suitable support, such as silica or silica-coated magnetic nanoparticles (γ-Fe2O3@SiO2), followed by reduction. This simple approach allows the synthesis of materials based on a network of secondary and tertiary amines. Materials were characterized by13C cross-polarization magic angle spinning NMR (13C CPMAS NMR), proton spin-lattice relaxation times in the rotating frame (T1ρH) and thermogravimet…

Heterogenizing palladium tetraiodide catalyst for carbonylation reactions

We report the first example of successful heterogenization of the classical PdI42- carbonylation catalyst, achieved in two simple steps from ionic liquid-functionalized multi-walled carbon nanotubes (MWCNTs). The newly developed materials (PdI4@MWCNT-imi-X, X = Br, I) present the PdI42- anion supported on an imidazolium network (imi) grown on MWCNTs and have been fully characterized. The activity of PdI4@MWCNT-imi-X has been successfully tested in a paradigmatic carbonylation reaction, the oxidative monoaminocarbonylation of 1-alkynes with amines to give high value added 2-ynamides (obtained in good yields, 50–84%, starting from various substrates). The heterogeneous catalyst could be easil…

Effect of halloysite nanotubes filler on polydopamine properties

Abstract Hypothesis Polydopamine (PDA) is widely used as hydrophilic coating for several applications. However, most of the methods studied to improve or manipulate PDA properties are multistep and time-consuming, and there is a need for versatile strategies aimed at controlling and modifying the properties of PDA. Experiments PDA-halloysite nanocomposites were produced under different oxidation conditions in alkaline and acidic media and were characterized by UV–visible and attenuated total refraction- Fourier Transform Infrared spectroscopies, thermogravimetric analysis, porosimetry, scanning electron microscopy, X-ray diffraction and contact angle measurements against the reference PDA p…

Thiazolium-based catalysts for the etherification reaction of benzylic alcohols under solvent-free condition

Thiazolium and imidazolium hybrid materials were prepared by radical reactions between a mercaptopropyl-modified SBA-15 mesoporous silica and bis-vinylthiazolium or bis-vinylimidazolium dibromide salts. These hybrid materials were characterized by several techniques and were employed in the etherification reaction of 1-phenylethanol. Solvent-free conditions at 160C under different gas phases (oxygen, air, nitrogen and argon) were used. The thiazolium-based material displayed excellent performances. Further studies were carried out using unsupported thiazolium salts, with or without a methyl group at the C-2 position of the thiazolium moiety. These studies allowed us to propose a reaction me…

Correction: Supported C60-IL-PdNPs as extremely active nanocatalysts for C–C cross-coupling reactions

Correction for ‘Supported C60-IL-PdNPs as extremely active nanocatalysts for C–C cross-coupling reactions’ by Francesco Giacalone et al., J. Mater. Chem. A, 2016, 4, 17193–17206.

A study of the behaviour of 2,4-substituted thiosemicarbazides toward orthoesters: Formation of mesoionic compounds

The reactions beetwen 2,4-disubstituted thiosemicarbazides and orthoesters in refluxing xylene led to the formation of the 1,2,4-triazoline-5-thione ring and to the 1,2,4-triazolium-5-thiolate ring. The formation of the mesoionic componds is due to rearrangement of the easily available 2,4-disubstituted thiosemicarbazides to 1,4-disubstituted thiosemicarbazides under the reaction conditions adopted. This method can be usefully used for the synthesis of mesoionic compounds, especially in the case of the 2-methyl-4-phenylthiosemicarbazide.

Recyclable Heterogeneous and Low-Loading Homogeneous Chiral Imidazolidinone Catalysts for α-Alkylation of Aldehydes

Two polystyrene-supported and six homogeneous MacMillan imidazolidinone catalysts were prepared and tested for the asymmetric α-alkylation of propanal with benzodithiolylium tetrafluoroborate. The chiral imidazolidinone was linked to polystyrene through the N-3 atom or through the phenyl ring and their catalytic activity was compared with that of their unsupported precursors. This comparison has allowed us to find an unsupported catalyst that displays high catalytic activity down to 5 or 2 mol % at room temperature with a high level of enantioselectivity also when used with hexanal and 3-phenylpropanal. In addition, one of the heterogeneous materials was revealed to be highly recyclable for…

New substituted imidazolidinone as low loading catalyst for α-alkylation of aldehydes

Sistemi TEMPO-C60 come Catalizzatori Riciclabili Attivi nell’Ossidazione di Alcoli

Modified nanocarbons as catalysts in organic processes

The application of nanocarbons as useful scaffolds for the production of a wide range of catalytic systems is an ever-growing field as witnessed by the huge amount of research on this topic. Both covalent and non-covalent modifications of nanocarbons represent the main routes to gain access to hybrid nanostructured catalysts. In this chapter the attention will be focused on nanocarbons, namely, fullerene, nanotubes, and graphene, employed for catalytic purposes covering both organocatalytic and metal-based (metal nanoparticles, organometallic complexes) reactions, whereas simple physical mixtures of nanocarbons and metal nanoparticles as well as examples dealing with electrocatalysis or pho…

GREEN CONDITIONS FOR THE SUZUKI REACTIONS BY USING MICROWAVE IRRADIATION AND MODIFIED HALLOYSITE/Pd CATALYST

Halloysite nanotube (HNT) is an emerging biocompatible material with appealing perspective for technological applications, such as in catalysis1 and in pharmaceutical research.2 Halloysite is a double-layered aluminosilicate mineral that has a predominantly hollow tubular structure. The functionalization of HNTs is a good strategy to introduce an organic moiety onto the external surface and, therefore, to obtain innovative catalyst supports.3 We have modified the external surface of halloysite nanotube with octylimidazolium moieties (HNT-IL) by microwave irradiation in solvent-free conditions and we have have employed this material as support catalyst of Pd nanoparticles. The new HNT/Pd cat…

Supported Imidazolium Functionalized POSS Hybrids as Palladium Platform for C-C Cross-Couplings

Lo sviluppo di catalizzatori per i processi di conversione della CO2 è una tematica che sta rivestendo un ruolo di rilevante importanza in ambito non soltanto accademico ma anche industriale grazie alla possibilità di trasformare un rifiuto, quale il diossido di carbonio, in una vasta gamma di prodotti. Nel presente lavoro, nuovi materiali ibridi costituiti da silsesquiossani poliedrici oligomerici (POSS) supportati su silice e funzionalizzati con sali di imidazolio sono stati progettati per la fissazione della CO2. 1 Tutti i solidi sono stati ampiamente caratterizzati e testati per la sintesi di carbonati ciclici tramite reazione tra CO2 ed epossidi in condizioni di reazione solvent-free (…

ChemInform Abstract: Novel Prolinamide-Supported Polystyrene as Highly Stereoselective and Recyclable Organocatalyst for the Aldol Reaction.

A new prolinamide derivative anchored to a polystyrene support has been straightforwardly prepared and employed as heterogeneous catalyst in the direct asymmetric aldol reaction with good results in terms of yield and stereoselectivity. The optimal reaction conditions were found when a 1:2 (v/v) water/chloroform mixture was used. This mixture was the best compromise between the good swelling properties of chloroform and the formation of a concentrated organic phase due to the presence of water. Noticeably, the enantioselectivities obtained employing acetone as ketone were, to the best of our knowledge, the highest achieved with a supported proline derivative. This catalyst can be easily rec…

Supported ionic liquids. New recyclable materials for L-proline-catalyzed aldol reaction

Cross-Linked Imidazolium Salts as Scavengers for Palladium.

Five imidazolium-based materials have been synthesised and used for the first time as palladium scavengers. Radical reactions of suitable bis-vinylimidazolium salts led to a series of insoluble materials through homo-polymerisation, immobilisation with a 3-mercaptopropyl-modified silica gel or co-polymerisation with ethylene glycol dimethylacrylate. These materials were screened as palladium scavengers with a set of palladium(0) and palladium(II) compounds in different solvents and at different starting amounts of palladium. In many cases, residual amounts of palladium were lower than 5 ppm, as requested for the manufacture of active pharmaceutical ingredients and fine chemicals. The applic…

Paper Functionalized with Nanostructured TiO2/AgBr: Photocatalytic Degradation of 2–Propanol under Solar Light Irradiation and Antibacterial Activity

A facile method to produce paper&ndash

A quantitative study of substituent effects on oxidative cyclization of some 2-aryl-substituted aldehyde thiosemicarbazones induced by ferric chloride and cupric perchlorate

As a development of our previous work, we performed a kinetic study of the oxidative cyclization reaction of some 2,4-diaryl-substituted aldehyde thiosemicarbazones 1a-n induced by ferric chloride and by cupric perchlorate. The results of cyclization of 1a-n were compared to those of the corresponding 2-methyl derivatives. The kinetic data were analyzed by means of the Hammett's equation.

Stereoselective synthesis: from organoselenium to organocatalysis

Imidazolium-Functionalized Carbon Nanohorns for the Conversion of CO2 Unprecedented Increase of Catalytic Activity after Recycling

Carbon nanohorns (CNHs) were selected as a novel catalytic platform for the design of imidazolium based hybrid materials able to promote the conversion of carbon dioxide into cyclic carbonates. Several heterogeneous catalysts were prepared using a one-step procedure based on the radical polymerization of various bis-vinylimidazolium salts in the presence of pristine CNHs. The as-synthesized materials were tested for the fixation of CO2 into epoxides. The excellent catalytic performances were evaluated in terms of turnover number and productivity. The versatility of the above hybrids was proved using several epoxides as substrate. Catalysts recyclability was successfully verified for several…

Materiali catalitici a base di nanoparticelle di palladio immobilizzate su nanoforme di carbonio

Studies on the Stereoselective Selenolactonization, Hydroxy and Methoxy Selenenylation of α- and β-Hydroxy Acids and Esters. Synthesis of δ- and γ-Lactones.

Abstract The diastereoselective synthesis of hydroxy substituted γ- and δ-lactones was accomplished following two approaches. A 5- or 6-endo cyclization promoted by electrophilic selenium reagents of α- or β-hydroxy acids and a 5- or 6-exo cyclization of hydroxy esters obtained through a diastereoselective hydroxy selenenylation reaction of α- or β-hydroxy esters. Moreover, the diastereoselective methoxy selenenylation of the above compounds was investigated showing a case in which the compound that was unreactive in the hydroxy selenenylation conditions gave, in the methoxy selenenylation conditions, the deprotected diol. The usefulness of the methoxy selenenylation procedure was proven by…

Organocatalytic Alcohol Oxidation Catalyzed by Recyclable TEMPO-functionalized [60]fullerene

Synthesis and characterization of new polyamino-cyclodextrin materials.

With the aim of the synthesis of chemically modified cyclodextrins bearing polyamine pendant groups, potentially useful as capping agents for the preparation of nanosized metal systems or as auxiliaries for gene transfection, the reaction between the heptakis-(6-iodo)-(6-deoxy)-b-cyclodextrin and various polyamines has been explored. This synthetic approach allows obtaining materials constituted by mixtures of cyclodextrins, having different degrees of substitution, which were satisfactorily characterized by means of various complementary techniques (ESI-MS, NMR, potentiometric titration). The products obtained were successfully subjected to preliminary tests for their binding abilities tow…

Front Cover Picture: SBA‐15/POSS‐Imidazolium Hybrid as Catalytic Nanoreactor: the role of the Support in the Stabilization of Palladium Species for C−C Cross Coupling Reactions. (Adv. Synth. Catal. 16/2019)

Proline- and prolinamide-supported polystyrene: powerful and highly recyclable organocatalysts for the asymmetric aldol reaction

Supported proline and proline-derivatives as recyclable organocatalysts

In the last eight years, L-proline and L-proline derivatives, such as substituted prolinamides or pyrrolidines, have been successfully used as organocatalysts in several reactions. In this critical review we summarize the immobilization procedures of such organocatalysts highlighting their application, recoverability and reusability (86 references).

Paper-TiO2 composite: An effective photocatalyst for 2-propanol degradation in gas phase

Two simple routes for the synthesis of a paper-TiO2 composite were tuned up and the efficiency of the resulting paper-TiO2 photocatalyst was investigated in the 2-propanol oxidation in gas phase. The first route involved the in-situ generation over the sheet of paper of a TiO2 layer starting from a solution of Ti (OBu)4 in tert-butanoliacetic acid, followed by hydrothermal treatment at 120 degrees C for 3 h. The sample was labelled as paper-TiO2 (H). The second approach was based on the adsorption on the paper of a ready-made suspension of titania nanoparticles (TiO2 sol), generated in autoclave at 140 degrees C and stable in acid medium at pH <3. The sample was labelled as paper-TiO2 (S). …

Thiazolium-­‐based catalysts for the etherification of benzylic alcohols under solvent-­free conditions

In this work, thiazolium and imidazolium hybrid materials (SBA-15-Thia and SBA-15-Imi) were prepared by grafting the bis-vinylthiazolium or imidazolium salts onto thiol functionalized SBA-15 mesostructured silica. The catalytic activity was tested for the etherification of 1-phenylethanol, in heterogeneous conditions. The reactions were performed under different gas phases and reaction times. The SBA-15-Thia displayed an excellent catalytic performance, also with others benzyl alcohols. This material was successfully used in seven consecutive runs. Further studies were carried out in homogenous conditions. The results obtained allow proving that oxygen play an active role in the reaction pr…

A Liquid-Liquid Biphasic Homogeneous Organocatalytic Aldol Protocol Based on the Use of a Silica Gel Bound Multilayered Ionic Liquid Phase

An innovative two stage liquid–liquid biphasic homogeneous protocol for the asymmetric organocatalytic aldol reaction is proposed, based on the use of the cis-ion-tagged proline 8 dissolved in the liquid film of a multilayered ionic liquid covalently bonded to silica gel 4. The resulting catalytically active material 9 is first soaked with cyclohexanone in the presence of water, resulting in a semi-transparent gel, then the aldehyde is added and the mixture stirred at RT. In the first stage, 4 acts as a catalyst reservoir that delivers 8 to the cyclohexanone phase allowing the reaction to take place homogeneously. In the second stage, cyclohexanone is removed under vacuum and the resulting …

Simple and low loading catalysts for asymmetric aldol reaction under aqueous condition

ChemInform Abstract: Supported Proline and Proline-Derivatives as Recyclable Organocatalysts

In the last eight years, L-proline and L-proline derivatives, such as substituted prolinamides or pyrrolidines, have been successfully used as organocatalysts in several reactions. In this critical review we summarize the immobilization procedures of such organocatalysts highlighting their application, recoverability and reusability (86 references).

ChemInform Abstract: Covalently Supported Ionic Liquid Phases: An Advanced Class of Recyclable Catalytic Systems

In this review, the most recent advances in the synthesis and catalytic applications of covalently supported ionic liquid (IL) phases will be discussed. This class of recyclable catalytic materials is based on the covalent attachment of several types of ammonium salts, usually imidazolium, but also thiazolium, triazolium, and pyrrolidinium salts, on the surface of different supports, for example, silica, periodic mesoporous organosilica, polystyrene, magnetic-based materials, carbon nanotubes (NTs), halloysite NTs, polyhedral oligomeric silsesquioxane (POSS), and fullerenes. Moreover, poly(ionic liquid) materials, in which the IL-based structure also acts as a support, will be considered. T…

Protonation equilibria of some ortho-substituted and annelated aryl and thiophen-2-yl and -3-yl ketones

For some phenyl- (1–8) and thiophen-2-yl (9–11) and thiophen-3-yl (12–14) ketones quantum-mechanical (PM3) calculations have been performed, and for compounds 2, 3, 5–8, 10–14 protonation equilibria have been determined. Phenyl ketones have similar values for the m* parameter and show good linear correlation between the proton affinities calculated in the gas phase and the measured pKBH+ values, which in turn parallel the trend for the calculated carbonyl–phenyl ring dihedral angle. It appears that the differences in basicity are governed essentially by “internal” factors (carbonyl–ring conjugation), while the base–conjugate acid differential solvation is not significantly affected by struc…

Imidazolium-Functionalized Carbon Nanohorns for the Conversion of Carbon Dioxide

Six new hybrid materials composed of carbon nanohorns (CNHs) and highly cross-linked imidazolium salts were easily synthesized using a one-step procedure based on the radical oligomerization of bis-vinylimidazolium salts (bVImiX) in the presence of pristine CNHs. The hybrid materials were characterized and employed as the sole catalysts for the conversion of carbon dioxide into cyclic carbonate by reaction with epoxides. The solids displayed excellent turnover number and productivity. Moreover, four catalysts were investigated in recycling experiments. Two catalysts containing an octyl linker between the imidazolium units and a bromide or an iodide anion showed no loss in activity after thr…

Supported Organocatalysts as a Powerful Tool in Asymmetric Synthesis

Regioselective Epoxide Ring Opening. Steroselective Synthesis of a Tetrahydropyran Ring

The stereoselective synthesis of a 2-substituted tetrahydropyran with adjacent alkoxy-bearing stereogenic centre is described. The key steps of this synthesis were the stereoselective epoxidation of an allylic alcohol and the regioselective epoxide ring opening by lithium aluminum hydride. The regio and stereoselective synthesis of a trihydroxyselenide and a trihydroxysulfide is also described. The latter compounds are not suitable for cyclization to tetrahydrofuran ring.

Advances in organic and organic-inorganic hybrid polymeric supports for catalytic applications

In this review, the most recent advances (2014–2016) on the synthesis of new polymer-supported catalysts are reported, focusing the attention on the synthetic strategies developed for their preparation. The polymer-supported catalysts examined will be organic-based polymers and organic-inorganic hybrids and will include, among others, polystyrenes, poly-ionic liquids, chiral ionic polymers, dendrimers, carbon nanotubes, as well as silica and halloysite-based catalysts. Selected examples will show the synthesis and application in the field of organocatalysis and metal-based catalysis both for non-asymmetric and asymmetric transformations.

Oxidative cyclization of some aldehyde semicarbazones induced by metallic salts

The oxidative cyclization of some aldehyde semicarbazones 10 with four different oxidizing agents has been effected. The structure of the semicarbazones and the nature of cyclizing agent affected the rate and yield of cyclization but they did not show any influence on the regiochemistry of reaction. In fact, 1,2,4-triazoline 20 was the only heterocyclic ring obtained by the cyclization reaction.

New recyclable catalysts for direct asymmetric aldol reaction. L-proline or H-Pro-Pro-Asp-NH2 immobilized on new ionic liquid modified silica gels

“Nonsolvent” Applications of Ionic Liquids in Organocatalysis

This chapter is organized in three sections (see Figure 10.1 ): 2. Immobilization of ionic liquids and organocatalysts 2.1 Covalently attached “ ionic liquid ” moieties as supports 2.2 Covalently attached “ ionic liquid ” moieties as linkers 2.3 Covalently attached “ ionic liquid ” moieties as organocatalysts

Site-specific halloysite functionalization by polydopamine: A new synthetic route for potential near infrared-activated delivery system

Abstract Halloysite nanotubes (HNTs) represent a versatile core structure for the design of functional nanosystems of biomedical interest. However, the development of selective methodologies for the site-controlled functionalization of the nanotubes at specific sites is not an easy task. This study aims to accomplish a procedure for the site-selective/specific, “pin-point”, functionalization of HNTs with polydopamine (HNTs@PDA). This goal was achieved, at pH 6.5, by exploiting the basicity of ZnO nanoparticles anchored on the HNTs external surface (HNTs@ZnO) to induce a punctual polydopamine polymerization and coating. The morphology and the chemical composition of the nanomaterial was demo…

Single-Walled Carbon Nanotube–Polyamidoamine Dendrimer Hybrids for Heterogeneous Catalysis

We report the synthesis and catalytic properties of single-walled carbon nanotube-polyamidoamine dendrimers hybrids (SWCNT-PAMAM), prepared via a convergent strategy. The direct reaction of cystamine-based PAMAM dendrimers (generations 2.5 and 3.0) with pristine SWCNTs in refluxing toluene, followed by immobilization and reduction of [PdCl4](2-), led to the formation of highly dispersed small palladium nanoparticles homogeneously confined throughout the nanotube length. One of these functional materials proved to be an efficient catalyst in Suzuki and Heck reactions, able to promote the above processes down to 0.002 mol % showing a turnover number (TON) of 48 000 and a turnover frequency (T…

Fullerene as a Platform for Recyclable TEMPO Organocatalysts for the Oxidation of Alcohols

[60]Fullerene has been employed successfully as a molecular platform to anchor 12 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) moieties. Such an octahedrally substituted C60-derivative has been employed as an organocatalyst for the oxidation of primary and secondary alcohols using the Anelli protocol. The reaction showed a general applicability to various alcohols, and the catalyst was recovered easily and could be recycled for at least seven cycles with no loss in catalytic activity. EPR spectroscopy studies revealed that the amount of radicals decreases during the catalytic cycles, even if the recovered material still displays unchanged catalytic activity. This new approach paves the way …

Water in stereoselective organocatalytic reactions

In this review, recent advances in asymmetric organocatalytic reactions carried out with variable amounts of water, from substoichiometric to a large excess (reaction medium), are discussed. We also summarize several proposed mechanisms for the different possibilities of the action of water both in the increased activity of the catalyst and in the asymmetric induction. Finally, the application of this catalytic methodology to the enantioselective synthesis of valuable compounds through enamine or iminium catalysis is presented.

Improved performance in flexible organic solar cells by using copolymeric phase-separation modulators

One of the main problems related to the low performance of the organic solar cells (OSCs), concerns the low mobility of the materials constituting the heterojunction. Indeed, the poor charge transport in the active layer is the principal cause of a competition between separation and recombination of the photogenerated carriers. In this regard, a major obstacle to enhance OSCs efficiency is developing strategies to optimize the exciton dissociation and, consequently, the charge collection at the electrodes. Donor and acceptor systems must be well mixed on the length scale of 5 – 20 nm (exciton diffusion length) to meet the criteria for efficient exciton dissociation. In addition, the network…

Cyclodextrin-[60]fullerene conjugates: synthesis, characterization, and electrochemical behavior

Three different functionalized β-cyclodextrins (β-CDs) bearing the C60 moiety linked covalently have been prepared in good yields by reaction between the parent β-CD and [60]fullerene via 1,3-dipolar cycloaddition. These compounds have been fully spectroscopically characterized and their electrochemical behavior has been investigated. Surprisingly, the electrochemical properties of the C60 cage remain unaltered even after chemical functionalization, making these systems very appealing as supramolecular hosts for electron-transfer processes.

Imidazolium functionalized carbon nanotubes for the synthesis of cyclic carbonates: reducing the gap between homogeneous and heterogeneous catalysis

Single walled carbon nanotubes (SWCNTs) were functionalized with imidazolium salts bearing vinyl functionalities. An extremely high loading of active species was achieved through a straightforward one-pot procedure involving self-assembly of the imidazolium moieties followed by radical initiated polymerization of the double bonds. The materials were extensively characterized by transmission electron microscopy, Raman spectroscopy, nitrogen physisorption and combustion chemical analysis. The imidazolium functionalized SWCNTs displayed excellent catalytic activity for the reaction of CO2 and epoxides to produce cyclic carbonates as demonstrated by the excellent turnover numbers (TON). Moreove…

Catechol-Functionalized Carbon Nanotubes as Support for Pd Nanoparticles

Carbon nanotubes have been covalently functionalized with catechol moieties through the formation of the corresponding aryl radicals obtained by reacting 4-aminocatechol with isoamyl nitrite. The functionalized multiwalled carbon nanotubes have been in turn used to immobilize Pd(II) ions on its surface forming catechol-Pd complexes, which were reduced to Pd nanoparticles (NPs). The so-obtained hybrid material has been characterized by means of thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). This latter technique allowed to estimate the nanoparticle size (5.7 +/- 2.8 nm) wh…

A joint experimental and computational study on the oxidative cyclization of aldehyde thiosemicarbazones induced by potassium ferricyanide and by tris(p-bromophenyl)amino hexachloroantimoniate.

NON-CONVENTIONAL TECHNIQUES IN ORGANIC SYNTHESIS

New recyclable materials for L-proline-catalyzed aldol reactions

Stereocontrolled approach to δ- and γ-lactones and 1,3-diols. The role of X− ion in the selenolactonization

Abstract Two complementary approaches have been realized for the stereoselective synthesis of 4,6-disubstituted δ-lactones and 1,3- anti and syn diols. In the 6- endo selenolactonization the role of the X − ion on the stereoselectivity is shown. Moreover, the highly stereoselective transformation of the 6- endo δ-lactone to the 5- exo γ-lactone is reported.

A spectrofluorimetric study of binary fluorophore-cyclodextrin complexes used as chiral selectors

Abstract Six binary complexes between three fluorophores (pyrene, xanthone and anthraquinone) and β-cyclodextrin (β-CD) or heptakis-(6-amino)-(6-deoxy)-β-cyclodextrin (am-β-CD) were tested at two pH values (8.0 and 9.0) as chiral selectors for three α-amino acids chosen as model. The conditional constant (β2T) values for ternary complexes (fluorophore-CD-amino acid), determined by means of fluorescence spectroscopy, showed that the binary complexes are suitable receptors for chiral recognition. The effect of α-amino acids on stability and stoichiometric ratio of the binary complexes has also been studied. The binary complexes were in most cases stabilized by adding the ternary agent. The tr…

Spectrophotometric study on the thermodynamics of binding of α- and β-cyclodextrin towards some p-nitrobenzene derivatives

Binding properties of native alpha- and beta-cyclodextrin towards some nitrobenzene derivatives have been studied by means of UV-vis spectrophotometry. The former host is able to form complexes having 1 : 1 and 1 : 2 stoichiometric ratios with these guests, while only 1 : 1 complexes are detected with the latter host. A careful analysis of the thermodynamic parameters for complexation equilibria, under the perspective of the enthalpy-entropy compensation effect, reveals that binding abilities of the two different hosts are subject to different features.

Polarimetry as a useful tool for the determination of binding constants between cyclodextrins and organic guest molecules

Binding constants for cyclodextrin inclusion complexes can be easily estimated by means of simple polarimetric measurements. Determinations are as reliable and accurate as those obtained by means of other more sophisticated techniques, and take advantage by the limited waste of material required. Our results are briefly compared with literature values obtained by means of different techniques.

Complexation equilibria between beta-cyclodextrin and p-nitroaniline derivatives in mixed solvent media: a polarimetric study

ChemInform Abstract: Stereocontrolled Approach to δ- and γ-Lactones and 1,3-Diols. The Role of X- Ion in the Selenolactonization.

Abstract Two complementary approaches have been realized for the stereoselective synthesis of 4,6-disubstituted δ-lactones and 1,3- anti and syn diols. In the 6- endo selenolactonization the role of the X − ion on the stereoselectivity is shown. Moreover, the highly stereoselective transformation of the 6- endo δ-lactone to the 5- exo γ-lactone is reported.

ChemInform Abstract: Sequential Suzuki/Asymmetric Aldol and Suzuki/Knoevenagel Reactions under Aqueous Conditions.

Here we describe for the first time a sequential Suzuki/asymmetric aldol reaction. Such sequential approach was achieved through the combined use of an ionic liquid supported palladium catalyst and the organocatalyst trans-4-(2,2-diphenylacetoxy)proline. Suzuki and asymmetric aldol reactions were performed under aqueous conditions. The use of a palladium catalyst under basic conditions allowed also the first example of sequential Suzuki/Knoevenagel reaction. Reactions were carried out under aqueous conditions and products were isolated in good to high yields and, in the case of the Suzuki/aldol reaction, with diastereoselectivities up to 91:9 and enantioselectivities up to at least 99 %.

Polystyrene-supported organocatalysts for alfa-selenenylation and Michael reactions. A common post-modification approach for catalytic differentiation

Three different resin-supported catalysts have been prepared by using the well established post-modification approach by means of thiol-ene coupling reaction. Two catalysts were tested for the first time in the asymmetric α-selenenylation of propanal, while the third catalyst was used in the Michael addition reaction. While the preliminary results are not encouraging in the case of supported Jørgensen’ catalyst, interesting data have been collected with both for the supported MacMillan and prolyl-prolinol catalysts. In fact, these catalysts displayed good activity and selectivity. A reversed enantioselectivity in the α-selenenylation was observed by changing the polarity of the solvent. Fin…

Supported Organocatalysts as a Powerful Tool in Organic Synthesis

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Immobilizzazione di dipeptidi su resina polistirenica ed impiego in sintesi stereoselettive: risultati preliminari

Heterocyclic photorearrangements. Photoinduced rearrangement of 3-styryl-1,2,4-oxadiazoles

The photochemical behaviour of 3-styryl-5-phenyl-(5-methyl)-1,2,4-oxadiazoles in methanol at 254 nm has been investigated. A photoinduced rearrangement to the quinoline system has been pointed out and explained as proceeding through an initial photolysis of the ring ON bond, followed by a six membered ring closure reaction involving the styryl moiety.

Catalytic Synergism in a C60IL10TEMPO2 Hybrid in the Efficient Oxidation of Alcohols

A novel fullerene (5:1)hexakisadduct bearing two 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) radicals and ten 1-propyl-3-methylimida- zolium bromide moieties has been synthesized and characterized. Such an C60IL10TEMPO2 hybrid has been successfully employed as a catalyst in the se- lective oxidation of a wide series of alcohols and is highly active at just 0.1 mol% loading. Moreover, it can be easily recovered by adsorption onto a multi- layered covalently-linked SILP phase (mlc-SILP) through a "release and catch" approach and reused for up to 12 cycles without loss in efficiency. Inter- estingly, a catalytic synergistic effect of TEMPO and imidazolium bromide moieties combined in the same…

Multi-layered, covalently supported ionic liquid phase (mlc-SILP) as highly cross-linked support for recyclable palladium catalysts for the suzuki reaction in aqueous medium

The reaction between an excess of 1,4-bis(3-vinylimidazolium-1-yl) bromide and a mercaptopropyl-modified amorphous silica gel or ordered mesoporous silica SBA-15 in the presence of azobisisobutyronitrile (AIBN) afforded new materials, which have a high loading of imidazolium moieties. These materials, which contain a highly cross-linked polymeric network, have been denoted as multi-layered, covalently supported ionic liquid phase (mlc-SILP) and have been used as support for palladium catalysts containing a high loading of the metal (10 wt%). Such materials were characterized by several techniques (13C magic angle spinning nuclear magnetic resonance, the Brunauer–Emmett–Teller technique, sma…

DNA-Binding and Anticancer Activity of Pyrene-Imidazolium Derivatives

DNA-binding investigations showed that two different derivatives endowed with pyrene and imidazolium moieties, 1 and 2, strongly bind both double-stranded DNA and telomeric sequences in G-quadruplex (G4) conformation. The values of the DNA-binding constants indicate that 1 and 2 show preferential affinity for G4-DNA, of about one and two orders of magnitude, respectively. Moreover, 1 and 2 inhibit short and long-term proliferation of breast cancer cell lines in a time- and dose-dependent fashion. Remarkably, senescence assays indicate that telomeric G4-DNA is a possible biotarget for the cytotoxic activity of 2. Molecular dynamics simulations suggest that the stronger binding of 2 with G4-D…

Organocatalizzatori e liquidi ionici supportati: nuovi materiali in sintesi organica

Nell’ultimo decennio l’organocatalisi e i liquidi ionici hanno rappresentato due campi di grande interesse scientifico. Gli organocatalizzatori hanno trovato particolare impiego in sintesi enantioselettive conducendo a prodotti finali con alte rese e selettività. I liquidi ionici sono stati estensivamente utilizzati come solventi alternativi e, opportunamente modificati, come catalizzatori o loro supporti. Uno sviluppo attuale che accomuna questi due campi di ricerca consiste nella possibilità di immobilizzazione di organocatalizzatori e liquidi ionici per trasformarli in materiali riciclabili con ampie capacità di utilizzo in chimica organica. Negli ultimi anni, il nostro gruppo di ricerca…

Templating effect of carbon nanoforms on highly cross-linked imidazolium network: Catalytic activity of the resulting hybrids with Pd nanoparticles

Two different carbon nanoforms (CNFs), namely multi-walled carbon nanotubes (MWCNTs) and carbon nanohorns (CNHs), have been chosen as support for the direct polymerization of a bis-vinylimidazolium salt. Transmission electron microscopy analyses revealed a templating effect of the CNFs on the growth of the polymeric network, which perfectly covers their whole surfaces creating a cylindrical or spherical coating for MWCNTs and CNHs, respectively. Subsequently, the CNFs-polyimidazolium have been used as stabilizers for Pd nanoparticles (Pd NPs), and the obtained materials have been characterized by means of analytical and spectroscopic techniques and then employed as easily recoverable and re…

Asymmetric aldol reaction in water catalyzed by polystyrene-supported proline

ChemInform Abstract: Sol-Gel Entrapped Chromium(VI): A New Selective, Efficient and Recyclable Oxidizing System.

Abstract The sol-gel entrapment of chromium(VI) within a silica matrix, obtained by oxidation with ozone of the corresponding entrapped chromium(III), was found to be an efficient and recyclable oxidizing system (at least up to 16 times) for benzylic alcohols. No leaching of chromium in solution was observed, which prevented any environmental pollution.

Covalently Supported Ionic Liquid Phases: An Advanced Class of Recyclable Catalytic Systems

In this review, the most recent advances in the synthesis and catalytic applications of covalently supported ionic liquid (IL) phases will be discussed. This class of recyclable catalytic materials is based on the covalent attachment of several types of ammonium salts, usually imidazolium, but also thiazolium, triazolium, and pyrrolidinium salts, on the surface of different supports, for example, silica, periodic mesoporous organosilica, polystyrene, magnetic-based materials, carbon nanotubes (NTs), halloysite NTs, polyhedral oligomeric silsesquioxane (POSS), and fullerenes. Moreover, poly(ionic liquid) materials, in which the IL-based structure also acts as a support, will be considered. T…

Catalytic properties of Ag-PolyaminoβCD NPs for reduction of nitroarenes

The reduction of nitroarenes is a key reaction involved in the synthesis of several compounds such as drugs, pesticides or dyes. During the last years Pd and Ag NPs have been used as catalysts to carry out this reaction with NaBH4. However several mechanistic aspects of the process are still unclear; in particular there is not agreement about the kinetic order of these reactions, whether 0-th or 1-st order in the substrate[1]. The aim of this work is to use a novel catalytic systems constituted by Ag-NPs coated with different polyamino-βCDs (Figure 1)[2], to carry out the reduction of some aromatic nitrocompounds using NaBH4 as the reducing agent, and to determine the kinetic features of th…

ChemInform Abstract: Gas-Phase and Solution Basicities of Some Alkyl 2,6-Dialkylphenyl Ketones: A Comparative Analysis.

Abstract The gas-phase basicity of a number of alkyl 2,6-dialkylphenyl ketones (2,6-R2C6H3COR′) has been found to be almost insensitive to structural variations, as a result of a compensation of steric and electronic effects associated with the bulkiness and to the polarizability, respectively, of R and/or R′. On the contrary, the basicity in concentrated sulfuric acid undergoes, along the same series of compounds, a variation of nearly 8 pK units, as a consequence of steric inhibition of solvation of the protonated carbonyl as the main effect played by R and/or R′. The results in the condensed phase agree very nicely with recent findings relevant to some 4-substituted 2,6-dimethylacetophen…

ChemInform Abstract: First Evidence of Proline Acting as a Bifunctional Catalyst in the Baylis-Hillman Reaction Between Alkyl Vinyl Ketones and Aryl Aldehydes.

Proline in the presence of sodium hydrogen carbonate has been found to be an effective catalyst for the Baylis–Hillman reaction between methyl or ethyl vinyl ketone and aryl aldehydes. Screening of several amine catalysts showed that an ionizable carboxylic function directly linked to the secondary amine catalyst plays an important role in the synthesis of the desired product in good yield. The data obtained has allowed us to suggest, for the first time, that proline, sarcosine, pipecolinic acid and homoproline may act as bifunctional catalysts via a bicyclic enaminolactone species as intermediate. Quantum-mechanical calculations (PM3/COSMO and ab initio 3-21G/COSMO) support this mechanism …

Piezoresistive semi-transparent flexible sensors by bithiophene fulleropyrrolidine thin films

Piezoresistive sensors are considered among the fundamental components of the future wearable electronic devices, given their potential applications in artificial skin, motion capture and personalized medicine.[1-5] Here, we present a cost-effective, viable fabrication approach to realize piezoresistive sensors using a novel polymeric biotiophene fulleropyrrolidine system (bis-C60Bi) synthesized on flexible ITO/PET supports by electrochemical chronoamperometry. By applying an anodic potential (1.5 V) to a solution containing the monomer, it is possible to obtain a homogeneous semi-transparent thin film on the ITO/PET surface (see Figure). AFM, XPS, UV-vis have been employed to characterize …

Sustainable Approach to Waste-Minimized Sonogashira Cross-Coupling Reaction Based on Recoverable/Reusable Heterogeneous Catalytic/Base System and Acetonitrile Azeotrope

In this contribution, we present a chemically efficient and sustainable protocol for the palladium-catalyzed copper-free Sonogashira cross-coupling reaction, based on the use of a heterogeneous catalytic system. This consists in the combination of a palladium catalyst on highly cross-linked thiazolidine network on silica and a polystyrene-supported base. The solid catalyst/base system acts as a palladium scavenger avoiding leaching of the metal and consequent product contamination. The reaction can be conducted in safe and easily recoverable acetonitrile/water azeotrope as reaction medium. This proved to be an efficient greener alternative to the classic toxic aprotic media commonly used in…

Diastereoselective Synthesis of 2-Phenylselenenyl-1,3-anti-Diols and 2-Phenylselenenyl-1,3-anti-Azido-Alcohols via Hydroxy- and Azido-Selenenylation Reactions

A method to synthesize 2-phenylselenenyl-1,3-anti-diols and 2-phenyl- selenenyl-1,3-anti-azidoalcohols via hydroxy- or azido-selenenylation of trans-allylic alcohols is reported. Moreover, the first example of hydroxyl-selenenylation of an allylic azide is presented. Yields ranging from moderate to good and diastereomeric ratios up to 95:5 are achieved.

ChemInform Abstract: Water in Stereoselective Organocatalytic Reactions

In this review, recent advances in asymmetric organocatalytic reactions carried out with variable amounts of water, from substoichiometric to a large excess (reaction medium), are discussed. We also summarize several proposed mechanisms for the different possibilities of the action of water both in the increased activity of the catalyst and in the asymmetric induction. Finally, the application of this catalytic methodology to the enantioselective synthesis of valuable compounds through enamine or iminium catalysis is presented.

Oxidative degradation properties of Co-based catalysts in the presence of ozone

Four series of cobalt-based catalysts, such as bare Co3O4 and CoO, CoOx-CeO2 mixed oxides, CoOx supported over alumina and alumina-baria and CoMgAl and CoNiAl hydrotalcites have been synthesized and investigated for the oxidative degradation of phenol in the presence of ozone. Characterizations were obtained by several techniques in order to investigate the nature of cobalt species and their morphological properties, depending on the system. Analyses by XRD, BET, TPR, UV-visible diffuse reflectance spectroscopy and TG/DT were performed. The CoNiAl hydrotalcite exhibits, after 4 h of reaction, the highest phenol ozonation activity followed by Co(3 wt%)/Al2O3-BaO and CoMgAl. The samples Co(1 …

Cross-Linked Thiazolidine Network as Support for Palladium: A New Catalyst for Suzuki and Heck Reactions

A thiazolidine-based material was used for the first time as support for palladium. The support was prepared by starting from a highly cross-linked thiazolium-based material, obtained by radical oligomerization of a bisvinylthiazolium dibromide salt in the presence of 3-mercaptopropyl-modified silica SBA-15. Palladium was immobilized by treatment with tetrachloropalladate salt. Reduction with sodium borohydride afforded a thiazolidine-based material that acted as ligands for the Pd species. The thiazolidine-based palladium catalyst was fully characterized and, working in only 0.1 mol% amount, displayed good activity in the Suzuki-Miyaura and in the Heck reactions. Several biphenyl and alken…

Supported C60-IL-PdNPs as extremely active nanocatalysts for C-C cross-coupling reactions

A C60-ionic liquid hybrid has been covalently linked to three different solid supports, namely amorphous silica, SBA-15 and Fe2O3@SiO2, and the resulting materials have been employed as covalently supported ionic liquid phases (cSILP) in order to immobilize and stabilize palladium nanoparticles (PdNPs). These novel hybrid materials are based on a sort of "matryoshka" system (PdNPs@imidazolium-salt@C60@support) in which the imidazolium-based moieties have not been directly linked to the surface of the support, but they are present in an octopus-like spatial arrangement on the uniformly surface-distributed fullerenes. These materials have been fully characterized and successfully employed as …

Water in Organocatalytic Reactions

Water is a green solvent: it is cheap, safe and environmentally friendly compared with organic solvents. Pfizer Corp. has defined a solvent guide that encourages the use of preferred solvents, for example, water or ethyl acetate, over usable solvents, for example, dimethyl sulfoxide (DMSO), and undesirable solvents, for example, dimethylformamide (DMF) [1]. However, chemical reactions carried out in or on water are not necessarily green reactions. Indeed, if we consider a reaction involving two species (A and B) and a product (C), the requirement for an ideal situation is when the product C has zero solubility and is quantitatively recovered by filtration, leaving no starting compounds A an…

Piezoresistive Sensors from Bithiophene-fulleropyrrolidine Bisadducts Thin-Films

The phenomenon of piezoresistivity in materials is based on the separation of conductive domains triggered by mechanical strains, resulting in a variation of the electrical resistance.1 This property is at the core of sensors for wearable electronics, e-skins, human motion detectors and machine learning devices.2 Fundamental requirements include lightness, good transparency, high flexibility and sensitivity to tiny deformations. However, the fabrication of a system integrating all these features is challenging. Herein, we show a semitransparent piezoresistive sensor realized by an electropolymerized bithiophene‐fulleropyrrolidine bisadduct onto ITO/PET3 (see Figure 1a). The good outcome of …

Sali di imidazolio multistrato supportati covalentemente: attività catalitica per la produzione di carbonati ciclici in scCO2 e nuovi supporti per catalizzatori di palladio

I liquidi ionici supportati (SILP) hanno trovato interessanti applicazioni sia nel campo delle reazioni catalizzate da metalli che in organocatalisi [1]. Inoltre, i SILP sono stati efficacemente impiegati in reazioni di apertura di epossidi in CO2 supercritica per fornire carbonati ciclici [2]. I liquidi ionici vengono generalmente supportati covalentemente attraverso la modificazione dei gruppi funzionali presenti sulla superficie del supporto, conducendo in tal modo alla formazione di un monostrato di liquido ionico supportato. Gli esempi di SILP legati covalentemente, in maniera tale da ottenere dei multistrato, sono rari. In questa comunicazione viene riportato un metodo per preparare d…

ChemInform Abstract: Stereoselective Synthesis of Substituted Tetrahydropyran Rings via 6-exo and 6-endo Selenoetherification.

Eight unsaturated alcohols were cyclized by selenoetherification in 6-exo or 6-endo manner to give substituted tetrahydropyran rings. Yields, regio- and stereoselectivities were discussed in terms of steric and electroniceffects such as Se-O interaction. For the first time examples of the use of silica gel in selenoetherification and the effect of the X - counter ion of PhSe + on the reaction course are discussed. These effects are related to the occurrence of Se-O interaction.

Chemical Fixation of Carbon Dioxide Catalysed by Multilayered Supported Ionic Liquids

Chemical modification of carbon nanomaterials (SWCNTs, DWCNTs, MWCNTs and SWCNHs) with diphenyl dichalcogenides

Control over chemical functionalization is a crucial point in the field of nanotechnology. Herein, we present the covalent functionalization of several carbon nanoforms (single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes and carbon nanohorns) by means of diphenyl dichalcogenides. These ones show different reactivity to the nanomaterials and are able to modify their electronic properties depending on the electronegativity of the functionalizing heteroatom. Theoretical calculations were also performed to support the experimental results. All the modified structured nanocarbons were thoroughly characterized by TGA Raman, XPS, UV/Vis/nIR, IR and TEM te…

Efficient Conversion of Carbon Dioxide by Imidazolium-Based Cross-Linked Nanostructures Containing Polyhedral Oligomeric Silsesquioxane (POSS) Building Blocks

Polyhedral oligomeric silsesquioxanes (POSS) have been employed as molecular building blocks for the synthesis of imidazolium cross-linked networks, to be used as heterogeneous catalysts for the conversion of carbon dioxide into cyclic carbonates. Two hybrid materials with different nucleophilic species (bromide and iodide) have been prepared and characterized by means of elemental analysis, 13C and 29Si solid-state NMR spectroscopy, thermogravimetric analysis and IR spectroscopy. The solids were tested as the sole catalyst under metal- and solvent-free reaction conditions showing full selectivity toward the formation of cyclic carbonates. High turnover number (TON) and productivity values,…

POSS nanostructures in catalysis

Polyhedral oligomeric silsesquioxanes (POSS) are organic-inorganic hybrid molecules piquing the interest of researchers thanks to their synergistic features. The great versatility of POSS nanostructures arises from the easy tunability of peripheral organic moieties combined with the high thermal and chemical stability of the inner inorganic core. In this review, we highlight the use of POSS nanostructures as molecular precursors for the synthesis of homogeneous and heterogeneous catalysts able to promote many processes including alkene epoxidation, C-C bond formation, CO2 conversion, "click reactions", hydrogenation, and ethylene polymerisation, among others. In this scenario, POSS units fo…

Sintesi efficiente mediata da microonde di derivati di fullerene per dispositivi fotovoltaici organici

Catalizzatori a base di nanocorni di carbonio-liquidi ionici per la conversione della CO2

Nel presente lavoro sono stati impiegati nanocorni di carbonio (CNHs) come piattaforma catalitica per il design di nuovi materiali ibridi a base di sali di imidazolio per la conversione della CO2 in carbonati ciclici. A tale scopo sono stati preparati una serie di catalizzatori eterogenei mediante una procedura sintetica one-pot basata sulla polimerizzazione radicalica di vari sali di bis vinilimidazolio in presenza di nanocorni di carbonio. I suddetti materiali sono stati caratterizzati e testati con successo per la reazione di fissazione della CO2 in epossidi (Figura 1). Figura 1 Conversione della CO2 catalizzata da liquidi ionici supportati su CNHs Le performances catalitiche, valutate i…

ChemInform Abstract: Eco-Friendly Functionalization of Natural Halloysite Clay Nanotube with Ionic Liquids by Microwave Irradiation for Suzuki Coupling Reaction.

Abstract Microwave assisted halloysite (HNT) external surface functionalization with ionic liquids is described. HNTs modification was achieved in two steps: a) grafting of 3-mercaptopropyl trimethoxysilane on the external surface of HNT by a microwave irradiation; b) anchorage of vinylimidazolium ionic liquids by a thiol-ene reaction. MW irradiation allowed us to obtain high loading onto the HNT surface compared to those obtained through conventional synthesis. Fourier transform infrared spectroscopy and thermogravimetric analysis confirmed that the grafting has occurred only on the external surface of HNT. Turbidimetric and dynamic light scattering analyses showed that the introduction of…

ChemInform Abstract: Oxidative Cyclization of Some Aldehyde Semicarbazones Induced by Metallic Salts.

The oxidative cyclization of some aldehyde semicarbazones 10 with four different oxidizing agents has been effected. The structure of the semicarbazones and the nature of cyclizing agent affected the rate and yield of cyclization but they did not show any influence on the regiochemistry of reaction. In fact, 1,2,4-triazoline 20 was the only heterocyclic ring obtained by the cyclization reaction.

Supported ionic liquids. New recyclable materials for the L-proline-catalyzed aldol reaction

New materials for L-proline recycling have been developed. These materials have been applied to the L-proline-catalyzed aldol reaction between acetone and several aldehydes. The L-proline has been supported on the surface of modified silica gels with a monolayer of covalently attached ionic liquid with or without additional adsorbed ionic liquid. Good yields and ee values, comparable with those obtained under homogeneous conditions, have been obtained especially with imidazolinium-modified and 4-methylpyridinium-modified silica gels. Moreover, these materials have been easily recovered by simple filtration and studies about their reuse have been carried out. These studies showed that these …

Hybrid paper–TiO2 coupled with a Cu2O heterojunction: an efficient photocatalyst under sun-light irradiation

Hybrid paper-TiO2, paper-Cu2O-TiO2 and paper-TiO2-Cu2O photocatalysts were prepared via a non-hydrolytic sol-gel process followed by mild hydrothermal treatment to generate the TiO2 layer, and a reduction process to form the Cu2O nanoparticles. The hybrid photocatalysts have been characterized by Raman, TGA, FE-SEM, UV-Vis and XPS. The immobilized TiO2 was found to form a homogeneous thin layer composed of nanoparticles with a size smaller than 10 nm. The Cu2O nanoparticles with sizes of 30-100 nm were generated either on the top of the TiO2 layer or by reduction of Cu2+ ions. All the prepared hybrid catalysts showed efficient photocatalytic properties for the degradation of toluidine when …

Substituent effect on oxidative cyclization of aldehyde thiosemicarbazones with ferric chloride

The reactivity of aldehyde thiosemicarbazones 1 with ferric chloride solutions was examined. When compounds 1 are not substituted on the N-2 nitrogen atom formation of 1,3,4-thiadiazole 3 heterocyclic ring was observed. In contrast 1,2,4-triazoline 4 and/or 1,3,4-thiadiazoline 5 heterocyclic rings were afforded when N-2 nitrogen atom carried a methyl or a phenyl group. The reaction mechanism is also discussed.

Carbon nanotube supported aluminum porphyrin-imidazolium bromide crosslinked copolymer

The increased awareness of the catastrophic consequences caused by the accumulation of greenhouse gases into the atmosphere has generated a large mobilization aimed at CO2 mitigation. Herein, in the spirit of the transformation of a waste as CO2 into value added products, we propose an efficient preparation of two different hybrid systems based on aluminum chloride tetrastyrylporphyrin (TSP-Al-Cl) and 1,4-butanediyl-3,3′-bis-1-vinylimidazolium dibromide copolymerized in the presence (MWCNT-TSP-AlCl-imi) and in absence (TSP-AlCl-imi) of multi-walled carbon nanotubes (MWCNTs) for the CO2 utilization in the synthesis of cyclic carbonates. The so-prepared materials have been thoroughly characte…

Recyclable organocatalysts

Oxidative cyclization of aldehyde thiosemicarbazones induced by potassium ferricyanide and by tris(p-bromophenyl)amino hexachloroantimoniate. A joint experimental and computational study

The oxidative ring closure reaction of some aryl-substituted thiosemicarbazones induced by "bona fide" one-electron abstracting agents was investigated, by means of both experimental and computational techniques. The corresponding 1,2,4-triazole derivatives were the only cyclization products observed. The occurrence of two slightly different mechanistic pathways for the reaction is discussed.

Synthesis and high-throughput testing of multilayered supported ionic liquid catalysts for the conversion of CO2 and epoxides into cyclic carbonates

Multilayered covalently supported ionic liquid phase (mlc-SILP) materials were synthesised by grafting different bis-vinylimidazolium salts on thiol-functionalised silica. These materials, which contain a cross-linked oligomeric network of imidazolium units, were characterised and tested as catalysts for the reaction of carbon dioxide with various epoxides to produce cyclic carbonates. The materials prepared by supporting a bis-imidazolium iodide salt with xylene or octane as a linker between the imidazolium units were identified as the most active catalysts and displayed high turnover numbers and improved productivity compared to known supported ionic liquid catalysts. The most promising m…

Spectrophotometric determinations of binding constants between cyclodextrins and aromatic nitrogen substrates at various pH values

The inclusion capacity of native β-cyclodextrin (1) and mono-(6-amino-6-deoxy)-β-cyclodextrin (2) versus aromatic compounds having a nitro or an amino group or both has been investigated at three different pH values. Molecular interactions in inclusion complexes have also been investigated by means of molecular mechanics (MM2/QD) models. Electrostatic and van der Waals interactions and the formation of a hydrogen bond between the donor amino group and the oxygen atom of the secondary hydroxyl group seem to be the more important contributions in determining complex stability. The inclusion capacity of two different cyclodextrins versus aromatic compounds has been investigated at three differ…

Synthesis of 2,4,6-trisubstituted tetrahydropyrans via 6-exo selenoetherification of unsaturated alcohols

Stereoselectivity, regioselectivity and yields in the 6-exo selenoetherification of four unsaturated diols were found to depend on the stereochemistry of the diols and on the presence of an oxygen atom close to the intermediate seleniranium ring. Silica gel was useful in order to obtain good yields. Reactions performed both under kinetic and thermodynamic control led to the same products. Stereoselectivity, regioselectivity and yields in the 6-exo selenoetherification of four unsaturated diols were found to depend on several factors such as the stereochemistry of the diols, the nature of the R group, the nature of the counter anion of the PhSe+ species and the presence of silica gel.

Advances towards highly active and stereoselective simple and cheap proline-based organocatalysts

Ten 4-acyloxy-L-prolines were screened as catalysts at loadings of 2–0.1 mol-% for the direct asymmetric aldol reaction in water by using variable amounts of water. Among them, a new catalyst, the L-proline carrying a trans-4-(2,2-diphenylacetoxy) group, and a catalyst previously synthesized by us, the L-proline carrying a trans-4-(4-phenylbutanoyloxy) group, were found to be excellent catalysts for the aldol reaction between cyclohexanone or cyclopentanone and substituted benzaldehydes when employed in only 1 and 0.5 mol-%,respectively, at room temperature without additives. For such catalysts, high turnover numbers were obtained, which are among the highest values obtained for enamine org…

A study of the mechanism of the oxidative cyclization of benzaldehyde semicarbazones induced by cupric perchlorate in acetonitrile

Treatment of benzaldehyde semicarbazones 1a-i with cupric perchlorate in acetonitrile at 40 provided selectively the corresponding 1,2,4-triazolin-5-ones 2a-i. The relative rate constants for 2a-i formation were determined by the competitive method. The results obtained showed that electron-donating substituents (methyl and methoxy) increase the reaction rate, while the reverse was found for electron-withdrawing substituents (chloro and nitro group). The reactivity data are discussed on the grounds of two possible mechanisms.

Polystyrene-supported proline and prolinamide. Versatile heterogeneous organocatalysts both for asymmetric aldol reaction in water and α-selenenylation of aldehydes

A simple and efficient synthesis of polystyrene-supported proline and prolinamide has been carried out. Polystyrene-supported proline has been used as organocatalyst in the asymmetric aldol reaction between cyclohexanone and substituted benzaldehydes in water without any additive. High yields, diastereoselectivities and ee values have been observed. The versatility of this resin was demonstrated in the α-selenenylation of aldehydes. Both proline and prolinamide resins gave high yields. Recycling studies showed that the proline resin gave better results than prolinamide resin.

Sol-gel entrapped chromium(VI): a new selective, efficient and recyclable oxidizing system

Abstract The sol-gel entrapment of chromium(VI) within a silica matrix, obtained by oxidation with ozone of the corresponding entrapped chromium(III), was found to be an efficient and recyclable oxidizing system (at least up to 16 times) for benzylic alcohols. No leaching of chromium in solution was observed, which prevented any environmental pollution.

Novel prolinamide-supported polystyrene as highly stereoselective and recyclable organocatalyst for the aldol reaction

A new prolinamide derivative anchored to a polystyrene support has been straightforwardly prepared and employed as heterogeneous catalyst in the direct asymmetric aldol reaction with good results in terms of yield and stereoselectivity. The optimal reaction conditions were found when a 1:2 (v/v) water/chloroform mixture was used. This mixture was the best compromise between the good swelling properties of chloroform and the formation of a concentrated organic phase due to the presence of water. Noticeably, the enantioselectivities obtained employing acetone as ketone were, to the best of our knowledge, the highest achieved with a supported proline derivative. This catalyst can be easily rec…

Cyclodextrin-[60]fullerene conjugates: Synthesis, characterization and electrochemical behavior

Supported Fullerene C60-Ionic Liquid Hybryds as New Catalytic Materials

Photochemical cyclization of some aldehyde thiosemicarbazones

The photochemical behaviour of some substituted aldehyde thiosemicarbazones 1a-k has been investigated in methanol at 254 nm. Thiosemicarbazones of glyoxil methyl ester 1a-f cyclized to furnish the 3-thioxo- 1,2,4-triazin-5-one 2 ring system. The remaining thiosemicarbazones 1g-j gave 1,2,4-triazoline 4 derivatives.

Chiral recognition of protected amino acids by means of fluorescent binary complex pyrene/heptakis-(6-amino)-(6-deoxy)-β-cyclodextrin

The ability of the binary complex pyrene (Py)/heptakis-(6-amino)-(6-deoxy)-β-cyclodextrin (am-β-CD) to act as a chiral selector was tested at two pH values (8.0 and 9.0). Phenylalanine (Phe), methionine (Met) and histidine (His) were used as chiral model molecules. The stability of ternary complexes Py/am-β-CD/amino acid was determined by means of spectrofluorimetric measurements. The data collected showed an increase in stability going from the binary to ternary complex and above all the possibility to use the binary complex as a chiral selector. Finally, data collected at two pH values showed that the binary complex is a better chiral selector when charged rather than in its neutral form.

Imidazolium Based Cross-Linked Nanostructures from POSS molecular bricks for the Efficient Conversion of Carbon Dioxide

Polyhedral oligomeric silsesquioxanes (POSS) have been employed as molecular bricks for the synthesis of imidazolium cross-linked networks as heterogeneous catalyst for the conversion of carbon dioxide into cyclic carbonates via reaction with epoxides. Two hybrid materials with different nucleophilic species (bromide and iodide) have been prepared and characterized by means of elemental analysis, 13C and 29Si solid state NMR, thermogravimetric analysis and IR spectroscopy. The solids were tested as the sole catalyst under metal- and solvent-free reaction conditions showing full selectivity toward the formation of cyclic carbonates and outstanding productivity values. Several epoxides were r…

Polystyrene-supported organocatalysts for α-selenenylation and Michael reactions

Abstract Three different resin-supported catalysts have been prepared by using the well established post-modification approach by means of thiol-ene coupling reaction. Two catalysts were tested for the first time in the asymmetric α-selenenylation of propanal, while the third catalyst was used in the Michael addition reaction. While the preliminary results are not encouraging in the case of supported Jorgensen’ catalyst, interesting data have been collected with both for the supported MacMillan and prolyl-prolinol catalysts. In fact, these catalysts displayed good activity and selectivity. A reversed enantioselectivity in the α-selenenylation was observed by changing the polarity of the sol…

A Simple Procedure for Oxidation of Alcohols using [Bis(acetoxy)iodo]benzene and a Catalytic Amount of Bromide Ions in Ethyl Acetate

Primary and secondary benzylic alcohols and secondary aliphatic alcohols were oxidized to the corresponding aldehydes and ketones by using [bis(acetoxy)iodo]benzene (BAIB) and a catalytic amount of bromide ions, from tetrabutylammonium bromide or KBr, in ethyl acetate. The catalytic role of the bromide ions was also highlighted in the oxidation of primary aliphatic alcohols and secondary allylic alcohols carried out in the presence of 1 mol% TEMPO.

Sequential Suzuki/Asymmetric Aldol and Suzuki/Knoevenagel Reactions Under Aqueous Conditions

Here we describe for the first time a sequential Suzuki/asymmetric aldol reaction. Such sequential approach was achieved through the combined use of an ionic liquid supported palladium catalyst and the organocatalyst trans-4-(2,2-diphenylacetoxy)proline. Suzuki and asymmetric aldol reactions were performed under aqueous conditions. The use of a palladium catalyst under basic conditions allowed also the first example of sequential Suzuki/Knoevenagel reaction. Reactions were carried out under aqueous conditions and products were isolated in good to high yields and, in the case of the Suzuki/aldol reaction, with diastereoselectivities up to 91:9 and enantioselectivities up to at least 99 %.

Gas-phase and solution basicities of some alkyl 2,6-dialkylphenyl ketones: A comparative analysis

Abstract The gas-phase basicity of a number of alkyl 2,6-dialkylphenyl ketones (2,6-R2C6H3COR′) has been found to be almost insensitive to structural variations, as a result of a compensation of steric and electronic effects associated with the bulkiness and to the polarizability, respectively, of R and/or R′. On the contrary, the basicity in concentrated sulfuric acid undergoes, along the same series of compounds, a variation of nearly 8 pK units, as a consequence of steric inhibition of solvation of the protonated carbonyl as the main effect played by R and/or R′. The results in the condensed phase agree very nicely with recent findings relevant to some 4-substituted 2,6-dimethylacetophen…

Short and efficient chemoenzymatic synthesis of goniothalamin

Cross-Linked Polyamine from Imidazolium-Based Materials: A Simple Route to Useful Catalytic Materials

Novel Imidazolium Based Catalyst for the Chemical Fixation of Carbon Dioxide

Bending Sensors Based on Thin Films of Semitransparent Bithiophene-Fulleropyrrolidine Bisadducts

In this study, a novel bithiophene‐fulleropyrrolidine bisadducts system (bis‐Th2PC 60 ) was synthesized and electropolymerized by chronoamperometry onto flexible ITO/PET substrates. The resulting semitransparent thin film was characterized by XPS, FT‐IR, cyclic voltammetry and optical techniques, confirming the good outcome of the electropolymerization process. AFM investigations permitted to highlight an inherent disordered granular morphology, in which the grain‐to‐grain separation depends upon the application of bending. The electrical resistance of the thin film was characterized as function of bending (in the range 0°‐90°), showing promising responsivity to low bending angles (10°‐30°)…

Binding properties of polyaminocyclodextrin materials towards polyanions and p-nitroaniline derivatives

New Mussel Inspired Polydopamine-Like Silica-Based Material for Dye Adsorption

A straightforward and economic procedure has been developed for the synthesis of a new polydopamine-like silica-based material that has been obtained by oxidation of catechol with KIO4 followed by reaction with 3-aminopropyltrimethoxysilane. All techniques adopted for characterization showed that the obtained material is rich in different functional groups and the morphological analyses revealed dimensions in the nanometric range. The hybrid material has been characterized by several techniques showing its polydopamine-like nature, and preliminary observations for dye adsorption have been reported.

POSS-Al-porphyrin-imidazolium cross-linked network as catalytic bifunctional platform for the conversion of CO2 with epoxides

Two heterogeneous catalysts were prepared with the aim of following the promising path of CO2 fixation into epoxides. The synthetic procedure involves a radical copolymerization of an octavinylsilsesquioxane as inorganic core building block and tetrastyrylporphyrin aluminum chloride monomer (TSP-AlCl) in presence (POSS-TSP-AlCl-imiBr) or in absence (POSS-TSP-AlCl) of a bis-vinylimidazolium bromide salt (bis-imiBr), in order to investigate if the bifunctional heterogeneous material can display better catalytic performance than the separate species. All the solids were fully characterized and tested in the synthesis of cyclic carbonates starting from CO2 and several epoxides. The synergic coo…

ChemInform Abstract: Heterocyclic Photorearrangements. Photoinduced Rearrangement of 3-Styryl-1,2,4-oxadiazoles.

The photochemical behaviour of 3-styryl-5-phenyl-(5-methyl)-1,2,4-oxadiazoles in methanol at 254 nm has been investigated. A photoinduced rearrangement to the quinoline system has been pointed out and explained as proceeding through an initial photolysis of the ring ON bond, followed by a six membered ring closure reaction involving the styryl moiety.

Supported Ionic Liquids: A Versatile and Useful Class of Materials.

Supported ionic liquids (SILs) represent a class of materials with peculiar properties and a huge potential regarding their possible applications in different fields of chemistry. Herein, we report our ongoing research about the use of SILs as support for organocatalysts, their role as catalysts themselves, and their application as support and stabilizers of palladium nanoparticles (PdNPs). The use of SILs based materials allowed achieving good results. Moreover, in some cases, after the functionalization of the catalytic species with an ion-tag moiety, a release and catch approach was employed in order to improve the catalytic activity and to facilitate the recovery of the hybrid system fo…

Fullerene-ionic-liquid conjugates: a new class of hybrid materials with unprecedented properties.

A modular approach has been followed for the synthesis of a series of fullerene-ionic-liquid (IL) hybrids in which the number of IL moieties (two or twelve), anion, and cation have been varied. The combination of C60 and IL give rise to new unique properties in the conjugates such as solubility in water, which was higher than 800 mg mL(-1) in several cases. In addition, one of the C60 -IL hybrids has been employed for the immobilization of palladium nanoparticles through ion exchange followed by reduction with sodium borohydride. Surprisingly, during the reduction several carbon nanostructures were formed that comprised nano-onions and nanocages with few-layer graphene sidewalls, which have…

Synthesis of New Materials

Green conditions for the Suzuki reaction using microwave irradiation and a new HNT-supported ionic liquid-like phase (HNT-SILLP) catalyst

A new catalytic system based on modified halloysite nanotubes was employed in the Suzuki reaction under microwave irradiation. A set of solvents, times and bases was screened and the best experimental conditions were obtained when the reactions were carried out for 10 min in water–ethanol at 120 °C in presence of K2CO3 as base. Good recyclability was observed. The new catalytic system was employed using either 1 mol% or 0.1 mol%. The palladium catalyst displayed good activity, allowing the synthesis of several biphenyl compounds in high yield working with only 0.1 mol% palladium loading. The application of microwave irradiation decreased the reaction time and also improved conversion with r…

Recyclable Catalyst Reservoir: Oxidation of Alcohols Mediated by Noncovalently Supported Bis(imidazolium)-Tagged 2,2,6,6-Tetramethylpiperidine 1-Oxyl

Bis(imidazolium)-tagged 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) catalysts were adsorbed on different supports such as silica gel, silica gel modified with highly cross-linked polymeric imidazolium networks, and highly cross-linked polymeric imidazolium networks entrapping magnetic particles. These systems provided a convenient tool for the oxidation of both primary and secondary alcohols working as recyclable reservoirs for the bis(imidazolium)-tagged TEMPO catalysts. By using EPR spectroscopy it was demonstrated that the catalyst was released as the corresponding oxoammonium salt in the solution during the recycling step, thus promoting the oxidative process in a homogeneous fashion. …

Organocatalysts and metal-based catalysts: a journey toward the development of new catalytic materials

Organocatalysis and metal-based catalysis represent two of the main pillars of catalytic reactions and have witnessed a huge interest in the last decade. Immobilization, recovery and reuse of these catalysts is of primary importance because of the large amount used especially in the case of organocatalysts. On the other hand, metal-based catalysts must be recovered even if used in low amount, in order to avoid contamination of the product. In this context, we started several years ago investigations on the use of supported ionic liquid phases for the asymmetric organocatalysis mediated by proline.1 This approach is an example of a “release and catch” catalytic system.2 Starting from this ex…

ChemInform Abstract: A Quantitative Study of Substituent Effects on Oxidative Cyclization of Some 2-Methylsubstituted Aldehydes. Thiosemicarbazones Induced by Ferric Chloride

In order to gain further mechanistical information about the cyclization of thiosemicarbazones and thiosemicarbazone-type substrates induced by metallic salts as oxidizing agents, we performed the synthesis of substrates 1a-s and a kinetic study of the oxidative cyclization of 1 to 5-imino-Δ2-1,3,4-thiadiazole 2 and 1,2,4-triazoline-5-thione 3 derivatives induced by methanolic ferric chloride solutions. The results of cyclization were compared to those of corresponding semicarbazones. The kinetic data were analyzed by means of the Hammett's equation and ρ values discussed.

Polystyrene-supported proline as recyclable catalyst in the Baylis–Hillman reaction of arylaldehydes and methyl or ethyl vinyl ketone

Abstract Polystyrene-supported proline has been used as co-organocatalyst (10 mol%) with imidazole (10 mol%) in the Baylis–Hillman reaction between methyl or ethyl vinyl ketone and arylaldehydes. Recycling studies showed that the proline resin can be used up to five cycles with high isolated yields. This study represents the first example of supported proline as heterogeneous catalyst in the above reaction and broaden the scope of this catalytic material.

Binding properties of mono-6-amino-beta-cyclodextrin towards p-nitroaniline derivatives: a polarimetric study

Supported Polyhedral Oligomeric Silsesquioxane-Based (POSS) Materials as Highly Active Organocatalysts for the Conversion of CO2

Very high turnover numbers (TON) and productivity values up to 7875 and 740 respectively have been obtained for the conversion of CO2 into cyclic carbonates by using hybrid materials based on imidazolium modified polyhedral oligomeric silsesquioxanes (POSS-Imi) grafted on amorphous silica (SiO2) and mesostructured SBA-15. The heterogeneous organocatalysts were easily prepared via a straightforward synthetic procedure allowing to generate high local concentration spots of imidazolium active sites surrounding the POSS core. This synthetic procedure is also a promising approach for the design of a wide library of hybrid functional materials. The materials do not possess other co-catalytic spec…

A polyhedral oligomeric silsesquioxane-based catalyst for the efficient synthesis of cyclic carbonates

Polyhedral oligomeric silsesquioxane functionalized with imidazolium chloride peripheries (POSS-Imi) was successfully synthesized through a novel synthesis protocol. The solid was extensively characterized via1H NMR, 13C NMR and IR spectroscopy as well as combustion chemical analysis, mass spectrometry and transmission electron microscopy. Moreover, an in-depth investigation through 29Si NMR was performed. POSS-Imi was used for the first time as a catalyst for the conversion of CO2 and epoxides into cyclic carbonates with excellent results in terms of both yield and selectivity. The catalyst displayed improved catalytic performance with respect to unsupported 1-butyl-3-methylimidazolium chl…

Palladium on pumice: new catalysts for the stereoselective semihydrogenation of alkynes to (Z)-alkenes

Abstract High selectivities (93–99%) and excellent stereoselectivities (>99%) in the semihydrogenation of CC triple bonds were achieved using palladium on pumice with a metal loading of 0.5, 1.5 or 3.0% wt as catalyst. The reactions were carried out in ethanol or tetrahydrofuran with only 2.5% of ethylenediamine allowing a self-terminating semihydrogenation independently on the CC triple bond.

Enhanced Activity and Stereoselectivity of Polystyrene-Supported Proline-Based Organic Catalysts for Direct Asymmetric Aldol Reaction in Water

Several polystyrene-supported proline dipeptides and a prolinamide derivative were prepared by thiol–ene coupling. These materials were used as catalysts for the direct asymmetric aldol reaction in water, and results compared with unsupported catalysts in water. Such an approach gave more active or stereoselective catalysts compared to the unsupported compounds, showing that our immobilization procedure may be useful to develop catalytic materials with enhanced performance. Moreover, these catalysts can be recovered and reused for at least nine times without loss of activity or can be easily regenerated when their activity has decreased. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, …

Highly cross-linked imidazolium salt entrapped magnetic particles – preparation and applications

Magnetic particles entrapped into highly cross-linked imidazolium salts were synthesized using a straightforward approach by radical polymerization of bis-vinylimidazolium salts in the presence of superparamagnetic iron oxide particles. Potential applications for these new materials as (i) catalysts for conversion of propylene oxide to propylene carbonate, (ii) supports for organocatalysts, and (iii) scavenger materials for palladium removal are outlined.

Tuneable Emission of Polyhedral Oligomeric Silsesquioxane Based Nanostructures that Self-Assemble in the Presence of Europium(III) Ions: Reversible trans-to-cis Isomerization

[EN] Hybrid nanostructures with switchable and reversible "blue-red-green" emission were efficiently synthesized. These nanostructures comprise polyhedral oligomeric silsesquioxanes (POSS) that behave as a nanocage that can be functionalized with terpyridine-based organic ligands, which can be easily complexed with europium (III) ions. The complexes were characterized by UV-Vis and fluorescence spectroscopy and their stoichiometry was also confirmed by H-1 NMR spectroscopy. In the presence of the Eu(III) ions, the octafunctionalized nanocages self-assemble to form 3D architectures that display an intense red-emission, especially in the solid state. The presence of an alkenyl group bridging …

ChemInform Abstract: Palladium on Pumice: New Catalysts for the Stereoselective Semihydrogenation of Alkynes to (Z)-Alkenes.

Abstract High selectivities (93–99%) and excellent stereoselectivities (>99%) in the semihydrogenation of CC triple bonds were achieved using palladium on pumice with a metal loading of 0.5, 1.5 or 3.0% wt as catalyst. The reactions were carried out in ethanol or tetrahydrofuran with only 2.5% of ethylenediamine allowing a self-terminating semihydrogenation independently on the CC triple bond.

Chemical Modification of Carbon Nanotubes with Sulfonylamides

First Evidence of Tris(catecholato)silicate Formation from Hydrolysis of an Alkyl Bis(catecholato)silicate

The hydrolysis of 3-ammoniumpropylbis(catecholato)silicate 1, giving two different silica-based materials containing different amounts of tris(catecholato)silicate, is reported. The latter species can be formed through an attack of catechol to the silicon atom in the pentacoordinate complex, in which the silicon-carbon bond is further activated toward electrophilic proton cleavage. The Knoevenagel reaction was used as a probe in order to test the availability of functional groups on the surface of such materials.

New Hybrid Organic-inorganic Multifunctional Materials Based on Polydopamine-like Chemistry

Taking inspiration from the chemistry of dopamine, a simple and economic synthetic approach toward the synthesis of a series of silica-based polydopamine-like materials has been developed. Mild conditions and easy manipulation are the strongest aspects of this methodology. Such hybrid materials were successfully used as recyclable catalysts for Knoevenagel reactions.

Chromia on silica and zirconia oxides as recyclable oxidizing system: structural and surface characterization of the active chromium species for oxidation reaction

Chromium oxide samples supported over silica and zirconia were prepared by wet impregnation of the supports with aqueous solution of CrO3. In order to investigate the influence of the preparation method on the chromium dispersion and oxidation state, one sample was prepared by sol-gel technique. The materials were structurally characterized by XRD analysis. The oxidation states of chromium species were investigated by XPS, DRS and TPR/TPO techniques. EPR analyses were also carried out for the sample Cr/SiO2, that due to the low crystalline state exhibits broad XPS signals. In this case, particular attention was paid to the presence of Cr(V) and Cr (III) species and their concentration. The …

Spectrophotometric determination of binding constants between some aminocyclodextrins and nitrobenzene derivatives at various pH values

Abstract The inclusion capacity of three modified cyclodextrins—namely mono-(6- N , N -dimethylamino-6-deoxy)- ( 3 ), mono-6-(2-aminoethyl)-amino-6-deoxy- ( 4 ) and mono-6-(2- N , N -dimethylaminoethyl)-amino-6-deoxy- ( 5 ) β-cyclodextrin, with six para -substituted nitrobenzenes ( A – F ) has been investigated at three different pH values. Molecular interactions in inclusion complexes have also been investigated by means of molecular mechanics (MM2/QD) models. The desolvation of the cyclodextrin is the most important factor in determining the binding ability of the various hosts. However, for a given host, electrostatic and van der Waals interactions and the formation of a hydrogen bond be…

Binary complexes heptakis-(6-amino)-(6-deoxy)-beta-cyclodextrin/fluorophore: structural investigation and chiral recognition

Proximity Effect using a Nanocage Structure: Polyhedral Oligomeric Silsesquioxane-Imidazolium Tetrachloro- palladate Salt as a Precatalyst for the Suzuki-Miyaura Reaction in Water

A polyhedral oligomeric silsesquioxane-imidazolium tetrachloropalladate salt (POSS-Imi-PdCl4) was prepared by the reaction of a polyhedral oligomeric silsesquioxane-imidazolium chloride salt (POSS-Imi-Cl) with PdCl2 and used as a pre-catalyst for the Suzuki-Miyaura reaction in water at 100 °C at a low loading (0.08-0.16 mol %). Biphenyl compounds were isolated in high to excellent yields. A comparison of the POSS-based catalyst with the corresponding catalyst without the nanocage structure (i.e., 1-butyl-3-methylimidazolium tetrachloropalladate) highlighted the role of the POSS structure to reach higher yields in the Suzuki-Miyaura reaction. This result is ascribed to a proximity effect of …

Polyhedral Oligomeric Silsesquioxane Based Catalyst for the Efficient Synthesis of Cyclic Carbonates

In this work, the synthesis of a novel imidazolium-based polyhedral oligomeric silsesquioxane (POSS-mim-Cl) material is presented. The new nanometer-size organosilica based compound was employed for chemical fixation of CO2 into epoxide under homogeneous conditions. The target reaction was represented by the obtention of cyclic carbonates starting from epoxides and CO2. Particularly, styrene oxide was chosen as reference substrate. In addition, different parameters (solvent, temperature, pressure of CO2, and mass of the catalyst) were modified to find the best condition for CO2 conversion. The catalyst POSS-mim-Cl displayed good catalytic performances, the best results being obtained at 40 …

ChemInform Abstract: New Simple Hydrophobic Proline Derivatives as Highly Active and Stereoselective Catalysts for the Direct Asymmetric Aldol Reaction in Aqueous Medium.

New 4-substituted acyloxyproline derivatives with different hydrophobic properties of the acyl group were easily synthesized and used as catalysts in the direct asymmetric aldol reaction between cyclic ketones (cyclohexanone and cyclopentanone) and several substituted benzaldehydes. Reactions were carried out using water, this being the best reaction medium examined. Screening of these catalysts showed that compounds bearing the most hydrophobic acyl chains [4-phenylbutanoate and 4-(pyren-1-yl)butanoate] provided better results. The latter catalysts were successfully used in only 2 mol% at room temperature without additives to give aldol products in excellent stereoselectivities. These resu…

FUNZIONALIZZAZIONE DELLA SUPERFICIE DELL’ALLOSITE MEDIANTE RISCALDAMENTO A MICROONDE

L’allosite (Al2Si2O5•2H2O), è un alluminosilicato naturale, chimicamente simile al caolino; essa ha una struttura tubolare cava dell’ordine dei micrometri (0.5-1 μm ) e un diametro interno dell’ordine dei nanometri (15 nm ). I nanotubi di allosite (HNT) presentano sulla superficie esterna gruppi SiO2 mentre su quella interna gruppi AlOH. Viste le caratteristiche strutturali, HNT trovano applicazioni come Host, fungendo in alcuni casi da nanoreattori. Tali applicazioni sono però limitate dall’idrofilia della superficie, sia interna che esterna. In questo lavoro è stata sviluppata una nuova metodologia sintetica che prevede l’ultilizzo delle microonde per ancorare organosilani come precursori…

Lipase-catalyzed resolution of β-hydroxy selenides

Abstract Eleven β-hydroxy selenides were kinetically resolved using an immobilized lipase (Amano PS-C II) in toluene in the presence of vinyl acetate at 30 °C. This approach provided, in several cases, both enantiomers in high enantiomeric excess. The role of the size of substituents and the behaviour of cyclic β-hydroxy selenides is also discussed. Enantiopure β-hydroxy selenides are useful building blocks. As an application of this chemistry, enantiopure (1 S ,2 R )-indene oxide was obtained in one step from the proper enantiopure β-hydroxy selenide.

Straightforward preparation of highly loaded MWCNT-polyamine hybrids and their application in catalysis

Multiwalled carbon nanotubes (MWCNTs) were easily and efficiently functionalised with highly cross-linked polyamines. The radical polymerisation of two bis-vinylimidazolium salts in the presence of pristine MWCNTs and azobisisobutyronitrile (AIBN) as a radical initiator led to the formation of materials with a high functionalisation degree. The subsequent treatment with sodium borohydride gave rise to the reduction of imidazolium moieties with the concomitant formation of secondary and tertiary amino groups. The obtained materials were characterised by thermogravimetric analysis (TGA), elemental analysis, solid state 13C-NMR, Fourier-transform infrared spectroscopy (FT-IR), transmission ele…

TiO2/Ag2O immobilized on cellulose paper: A new floating system for enhanced photocatalytic and antibacterial activities

Paper-TiO2-Ag2O floating photocatalysts were produced under mild condition and their photocatalytic activity for the degradation of aromatic amine under sunlight stimulant was investigated. Characterizations by Raman, XRD, XPS, DRS and PL confirmed the presence of TiO2 and Ag2O, and the morphology of the appended TiO2/Ag2O layer was probed by FE-SEM. The photocatalytic activity of the prepared samples was investigated by the degradation of aniline (AN) in water under simulated sun-light illumination and constrained conditions, i.e. non-stirring and non-oxygenation. The presence of Ag2O combined with TiO2 was shown to improve the resistance of paper to bacteria attack, thus increasing the du…

ChemInform Abstract: A Liquid-Liquid Biphasic Homogeneous Organocatalytic Aldol Protocol Based on the Use of a Silica Gel Bound Multilayered Ionic Liquid Phase.

Key feature of the title protocol is the use of a cis-ion-tagged proline dissolved in a liquid film on a multilayered ionic liquid covalently bound to silica. The resulting catalytically active material is soaked in cyclohexanone and water to form a semi-transparent gel which then reacts with the aldehyde.

Simple and Cheap Highly Active Proline-Based Organocatalysts

Asymmetric Synthesis Using Polymer-Immobilized Proline Derivatives

Design of novel imidazolium based nanostructures for sustainable catalytic applications

ChemInform Abstract: A Simple Procedure for the Oxidation of Alcohols Using [Bis(acetoxy)iodo]benzene and a Catalytic Amount of Bromide Ions in Ethyl Acetate.

Primary and secondary benzylic alcohols and secondary aliphatic alcohols were oxidized to the corresponding aldehydes and ketones by using [bis(acetoxy)iodo]benzene (BAIB) and a catalytic amount of bromide ions, from tetrabutylammonium bromide or KBr, in ethyl acetate. The catalytic role of the bromide ions was also highlighted in the oxidation of primary aliphatic alcohols and secondary allylic alcohols carried out in the presence of 1 mol% TEMPO.

ChemInform Abstract: Photochemical Cyclization of Some Aldehyde Thiosemicarbazones.

The photochemical behaviour of some substituted aldehyde thiosemicarbazones 1a-k has been investigated in methanol at 254 nm. Thiosemicarbazones of glyoxil methyl ester 1a-f cyclized to furnish the 3-thioxo- 1,2,4-triazin-5-one 2 ring system. The remaining thiosemicarbazones 1g-j gave 1,2,4-triazoline 4 derivatives.

Evidences of release and catch mechanism in the Heck reaction catalyzed by palladium immobilized on highly cross-linked-supported imidazolium salts

Abstract Palladium (10 wt%) on a highly cross-linked imidazolium-based material was used as catalyst in 0.1 mol% in the Heck reaction between several alkenes and aryl iodides. Products were obtained from good to high yields. Deeper investigations showed a release of Pd species in solution and their capture by the imidazolium-based support. When a sixfold amount of support was employed the re-captured Pd species (0.5–0.6 wt%) were not anymore catalytically active. This result represents a new interesting aspect of this work since the highly cross-linked imidazolium-based material can act also as Pd scavenger avoiding the release of the metal in solution. Important differences between Heck an…

Novel supported dipeptides as recyclable catalysts for asymmetric aldol reaction

Highly Loaded Multi-Walled Carbon Nanotubes Non-Covalently Modified with a Bis-Imidazolium Salt and their Use as Catalyst Supports

The surfaces of multi-walled carbon nanotubes (MWCNTs) were non-covalently modified using two bis-imidazolium dibromide derivatives having phenyl or pyrene groups. Due to the presence of the two pyrene groups the bis(pyren-1-ylmethylimidazolium) dibromide derivative was immobilised at a loading of about 15-16 wt %, whereas only <3 wt % of the phenyl derivative was immobilised. The presence of the two imidazolium cations helped the immobilisation of tetrachloropalladate ions after exchange with bromide ions. Tetrachloropalladate was used as pre-catalyst in several Suzuki-Miyaura carbon-carbon cross-coupling reactions in water or water/ethanol at 50 °C in only 0.1 mol % and compared with the …

Antifouling Systems Based on a Polyhedral Oligomeric Silsesquioxane-Based Hexyl Imidazolium Salt Adsorbed on Copper Nanoparticles Supported on Titania

The reaction of octakis(3-chloropropyl)octasilsesquioxane with four equivalents of 1-hexylimidazole or 1-decylimidazole gave two products labelled as HQ-POSS (hexyl-imidazolium quaternized POSS) and DQ-POSS (decyl-imidazolium quaternized POSS) as regioisomer mixtures. An investigation of the biological activity of these two compounds revealed the higher antimicrobial performances of HQ-POSS against Gram-positive and Gram-negative microorganisms, proving its broad-spectrum activity. Due to its very viscous nature, HQ-POSS was adsorbed in variable amounts on the surface of biologically active oxides to gain advantages regarding the expendability of such formulations from an applicative perspe…

Enhanced power-conversion efficiency in organic solar cells incorporating copolymeric phase-separation modulators

A new class of copolymers containing oligothiophene moieties with different lengths and fullerene units have been designed and prepared by an easy and inexpensive one-step synthetic approach. The incorporation of small quantities of these copolymers into bulk heterojunction (BHJ) solar cells with donor regioregular polythiophene (P3HT) and an acceptor fullerene derivate (PCBM) results in good control of the phase separation process without further affecting the BHJ optoelectronic properties. Indeed, under thermal annealing these copolymers allow the modulation of the growth of domains whose size depends on the length of the copolymer repetitive units. Domain size on the same length scale as…

C60-TEMPO-IL hybrid: “release and catch” organocatalyst for the oxidation of alcohols

Studio polarimetrico degli equilibri di inclusione tra ciclodestrine native ed opportuni guest modello alifatici e aromatici

Short and Efficient Chemoenzymatic Synthesis of Goniothalamin.

A high-yielding three-step synthesis of goniothalamin involving an enzymatic kinetic resolution in the presence of vinyl acrylate followed by ring-closing metathesis is discussed.

Direct asymmetric aldol reaction using polystyrene-supported proline amide

Efficient microwave-mediated synthesis of fullerene acceptors for organic photovoltaics

Two different processes, namely the Bamford–Stevens and [4 + 2] Diels Alder reactions, have been optimized under microwave irradiation for the functionalization of fullerenes. In this manner, all the main C60- and C70-based acceptor derivatives for organic solar cells such as PCBM, DPM, BHN and ICBA, have been prepared in higher yields and shorter reaction times with respect to the reported data. These findings represent a step forward toward the wide production of cheaper organic solar cells as a consequence of the cost abatement of the acceptors given by higher yields, lower waste production, and reduced reaction time which means a strong energy saving.

New proline derivatives as recyclable catalysts for aldol reaction

ChemInform Abstract: Low-Loading Asymmetric Organocatalysis

Asymmetric organocatalysis is now recognized as the third pillar of asymmetric synthesis. Recent years have witnessed increasing interest towards the use of highly active and stereoselective organocatalysts. This critical review documents the advances in the development of chiral organocatalysts which are systematically used in ≤3 mol% loading in all the sub-areas of the field, namely aminocatalysis, Bronsted acids and bases, Lewis acids and bases, hydrogen bond-mediated catalysis, phase transfer and N-heterocyclic carbene catalyses (194 references).

ChemInform Abstract: Enhanced Activity and Stereoselectivity of Polystyrene-Supported Proline-Based Organic Catalysts for Direct Asymmetric Aldol Reaction in Water.

Several polystyrene-supported proline dipeptides and a prolinamide derivative were prepared by thiol–ene coupling. These materials were used as catalysts for the direct asymmetric aldol reaction in water, and results compared with unsupported catalysts in water. Such an approach gave more active or stereoselective catalysts compared to the unsupported compounds, showing that our immobilization procedure may be useful to develop catalytic materials with enhanced performance. Moreover, these catalysts can be recovered and reused for at least nine times without loss of activity or can be easily regenerated when their activity has decreased. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, …

ChemInform Abstract: Recyclable Catalyst Reservoir: Oxidation of Alcohols Mediated by Noncovalently Supported Bis(imidazolium)-Tagged 2,2,6,6-Tetramethylpiperidine 1-Oxyl.

Binding equilibria between beta-cyclodextrin and p-nitro-aniline derivatives: the first systematic study in mixed water-methanol solvent systems.

Abstract Complexation equilibria, in mixed water–methanol solvent media, between native β-cyclodextrin and a set of suitably selected p -nitro-aniline derivatives were studied by means of polarimetry. The effects exerted by the organic co-solvent on the conditional inclusion free energies Δ G cond 0 and the differential molar optical rotations Δ Θ were thoroughly analyzed under the perspective of the enthalpy–entropy compensation effect. Experimental data suggest an intimate participation (‘dynamic co-inclusion’) of solvent molecules in the formation and in the conformational dynamics of the host–guest inclusion complex.

First Evidence of Proline Acting as a Bifunctional Catalyst in the Baylis–Hillman Reaction Between Alkyl Vinyl Ketones and Aryl Aldehydes

Proline in the presence of sodium hydrogen carbonate has been found to be an effective catalyst for the Baylis–Hillman reaction between methyl or ethyl vinyl ketone and aryl aldehydes. Screening of several amine catalysts showed that an ionizable carboxylic function directly linked to the secondary amine catalyst plays an important role in the synthesis of the desired product in good yield. The data obtained has allowed us to suggest, for the first time, that proline, sarcosine, pipecolinic acid and homoproline may act as bifunctional catalysts via a bicyclic enaminolactone species as intermediate. Quantum-mechanical calculations (PM3/COSMO and ab initio 3-21G/COSMO) support this mechanism …

The binary pyrene/heptakis-(6-amino-6-deoxy)-β-cyclodextrin complex: A suitable chiral discriminator. Spectrofluorimetric study of the effect of some α-amino acids and esters on the stability of the binary complex

The effect of some α-amino acids and their esters on the stability of the binary pyrene/heptakis-(6-amino-6-deoxy)-β-cyclodextrin (py/am-β-CD) complex has been studied by means of fluorescence spectroscopy at two pH values (8.0 and 9.0). The binary complex was generally stabilized by adding the ternary agent at pH 8.0. A more varied substrate effect is observed at pH 9.0 where am-β-CD is present in the uncharged form. The conditional constant (β2) values determined by L/D α-amino acids show that the binary complex is a suitable receptor for chiral recognition. The enantiomer selectivity values obtained, ranging from 1.2 up to 7.4, are generally higher than those reported for α-amino acids a…

New simple hydrophobic proline derivatives as highly active and stereoselective catalysts for the direct asymmetric aldol reaction in aqueous medium

New 4-substituted acyloxyproline derivatives with different hydrophobic properties of the acyl group were easily synthesized and used as catalysts in the direct asymmetric aldol reaction between cyclic ketones (cyclohexanone and cyclopentanone) and several substituted benzaldehydes. Reactions were carried out using water, this being the best reaction medium examined. Screening of these catalysts showed that compounds bearing the most hydrophobic acyl chains [4-phenylbutanoate and 4-(pyren-1-yl)butanoate] provided better results. The latter catalysts were successfully used in only 2 mol% at room temperature without additives to give aldol products in excellent stereoselectivities. These resu…

Heterogeneous catalytic degradation of phenolic substrates: catalysts activity

This review article explored the catalytic degradation of phenol and some phenols derivates by means of advanced oxidation processes (AOPs). Among them, only the heterogeneous catalyzed processes based on catalytic wet peroxide oxidation. catalytic ozonation and catalytic wet oxidation were reviewed. Also selected recent examples about heterogeneous photocatalytic AOPs; will be presented. In details, the present review contains: (i) data concerning catalytic wet peroxide oxidation of phenolic compounds over metal-exchanged zeolites, hydrotalcites, metal-exchanged clays and resins. (ii) Use of cobalt-based catalysts, hydrotalcite-like compounds, active carbons in the catalytic ozonation proc…

Binding properties of heptakis-(2,6-di-O-methyl)-β-cyclodextrin and mono-(3,6-anhydro)-β-cyclodextrin: a polarimetric study

The binding constants for the inclusion complexes formed between heptakis-(2,6-di-O-methyl)-β-cyclodextrin (MβCD) and mono-(3,6-anhydro)-β-cyclodextrin (AβCD) with a set of suitably selected organic guests, were measured by means of polarimetry. Measurements were carried out at various pH values in order to ensure the correct protonation state for ionizable guests. Experimental data suggest that the binding properties of MβCD may be rationalized considering the less polar and more hydrophobic character of the cavity, although similar variations in conformational/dynamic behaviour occur as for native βCD. On the other hand, AβCD shows some similarities with αCD, due to the significant distor…

Stereoselective synthesis of substituted tetrahydropyran rings via 6-exo and 6-endo selenoetherification

Eight unsaturated alcohols were cyclized by selenoetherification in 6-exo or 6-endo manner to give substituted tetrahydropyran rings. Yields, regio- and stereoselectivities were discussed in terms of steric and electroniceffects such as Se-O interaction. For the first time examples of the use of silica gel in selenoetherification and the effect of the X - counter ion of PhSe + on the reaction course are discussed. These effects are related to the occurrence of Se-O interaction.

Binding porperties of hetpakis-(2,6-di-O-methyl)-beta-cyclodextrin and mono-(3,6-anydro)-beta-cyclodextrin

Toward More Efficient Organocatalysts

Modified Carbon Nanoforms Systems for Asymmetric Catalysis

Thermodynamics of binding between α- and β-cyclodextrins and some p-nitro-aniline derivatives: reconsidering the enthalpy–entropy compensation effect

Abstract The thermodynamics of binding between native α- and β-cyclodextrin towards several p -nitro-aniline derivatives was examined, in order to gain further insights about the occurrence of different interaction modes for the two hosts. Valuable information was achieved regarding the ‘expanded hydrophobic sphere’ of α-cyclodextrin. Furthermore, very interesting and unexpected aspects of the behavior of β-cyclodextrin were enlightened, such as the crucial role played by hydrogen bond interactions. Experimental data were examined under the perspective of the ‘enthalpy–entropy compensation effect’, and some ideas about this topic are discussed.

Eco-friendly functionalization of natural halloysite clay nanotube with ionic liquids by microwave irradiation for Suzuki coupling reaction

Abstract Microwave assisted halloysite (HNT) external surface functionalization with ionic liquids is described. HNTs modification was achieved in two steps: a) grafting of 3-mercaptopropyl trimethoxysilane on the external surface of HNT by a microwave irradiation; b) anchorage of vinylimidazolium ionic liquids by a thiol-ene reaction. MW irradiation allowed us to obtain high loading onto the HNT surface compared to those obtained through conventional synthesis. Fourier transform infrared spectroscopy and thermogravimetric analysis confirmed that the grafting has occurred only on the external surface of HNT. Turbidimetric and dynamic light scattering analyses showed that the introduction of…

Reconsidering TOF calculation in the transformation of epoxides and CO2 into cyclic carbonates

Abstract The combination of Lewis acids and Lewis bases, currently defined as catalysts and co-catalysts (or promoter) respectively, in the reaction between epoxides and CO2 to give cyclic carbonates, is discussed, starting from examples in which the Lewis base was used in larger amount with respect to the Lewis acid. In these cases, turnover frequency (TOF) values have been usually calculated taking into account solely the amount of the Lewis acid employed. The occurrence of two distinct reaction pathways, one catalysed by the sole Lewis base and the other one catalysed by the Lewis acid/Lewis base couple, in which the Lewis acid alone does not play a catalytic role, should bring researche…

Palladium supported on cross-linked imidazolium network on silica as highly sustainable catalysts for the Suzuki reaction

Polystyrene supported L-proline: a recyclable organocatalyst for the asymmetric aldol reaction in the presence of water

Novel supported substituted prolinamide as recyclable catalyst for asymmetric aldol reaction

Spectrophotometric study on the thermodynamics of binding of α- and β-cyclodextrin towards some p-nitrobenzene derivativesElectronic supplementary information (ESI) available: Values of inclusion constants at different temperatures. See http://www.rsc.org/suppdata/ob/b3/b300330b/

Binding properties of native α- and β-cyclodextrin towards some nitrobenzene derivatives have been studied by means of UV-vis spectrophotometry. The former host is able to form complexes having 1 : 1 and 1 : 2 stoichiometric ratios with these guests, while only 1 : 1 complexes are detected with the latter host. A careful analysis of the thermodynamic parameters for complexation equilibria, under the perspective of the enthalpy–entropy compensation effect, reveals that binding abilities of the two different hosts are subject to different features.

New ionic liquid-modified silica gels as recyclable materials for L-proline- or H-Pro-Pro-Asp-NH2-catalyzed aldol reaction

l-proline and the tripeptide H-Pro-Pro-Asp-NH2 (1) have been supported, by adsorption, onto the surface of modified silica gels functionalized with a monolayer of covalently attached 1,2-dimethyl-imidazolium chloride, tetrafluoroborate or hexafluorophosphate ionic moieties, respectively. Three different linkers were used to attach the ionic liquid moiety to the surface of these supports. The resulting materials have been used as catalysts for the aldol reaction between acetone and several substituted benzaldehydes. Good yields and enantioselectivities, comparable to or better than those obtained under homogeneous conditions, were obtained. These materials are easily recovered by filtration,…

From covalently linked catalysts to "release and catch" catalytic systems

Low angle bending detection semi-transparent piezoresistive sensor

We designed, fabricated, and validated a piezoresistive bending sensor, a fundamental component of wearable electronic devices for monitoring human motion. The most diffused opaque carbon-based resistance flex sensors suffer from low detection for small bending angles. The sensor we here present is based on a semi-transparent active material (fulleropyrrolidine bisadducts polymer) and has the remarkable advantage of good electrical properties for low bending angles. The fabrication steps are effective since a pre-patterned ITO/PET surface is functionalized by chronoamperometric deposition, and the silver electrical contacts are inkjet printed. We propose a fitting function of the measured t…

Advantages in supporting chiral organocatalysts

An overview on the advances in supporting organocatalysts for their use and recycle in the asymmetric synthesis is presented, focusing on the main approaches for the immobilization and highlighting those examples in which supported and unsupported version of the catalyst behave similarly and high level of recyclability have been obtained.

Nanoparticelle di Ag-poliamminoCD come catalizzatori per la riduzione di nitrocomposti aromatici

Sistemi nanoparticellari di Argento protetti con poliammino-beta-ciclodestrine sono stati preparati, caratterizzati, e impiegati come catalizzatori per la riduzione con boroidruro di sodio di una serie di nitrocomposti aromatici modello 1-8. Tale reazione costituisce una interessante alternativa rispetto ai metodi di riduzione più comuni (LiAlH4, Zn/HCl), che prevedono l’uso di condizioni di reazione piuttosto drastiche. La cinetica della reazione considerata è stata approfonditamente studiata al fine di chiarire il ruolo meccanicistico del catalizzatore. E’ stato trovato, infatti, che il processo risulta di ordine misto rispetto al substrato, e che le costanti cinetiche apparenti di reazio…

Hydrophobically Directed Aldol Reactions: Polystyrene-SupportedL-Proline as a Recyclable Catalyst for Direct Asymmetric Aldol Reactions in the Presence of Water (Eur. J. Org. Chem. 28/2007)

The cover picture shows the aldol reaction between ketones and arylaldehydes carried out by using a polystyrene-supported L-proline catalyst. This material furnishes aldol products in high yields and stereoselectivities. Screening of solvents showed that these reactions take place only in the presence of water. This solvent effect, coupled with the high stereoselectivities observed, has been explained by the formation of a hydrophobic core in the inner surface of the resin with the hydrophilic proline moiety in the resin/water interface. Such a microenvironment promotes the aldol reaction and increases the stereoselectivity. Recycling investigations have shown that this material can be reus…

“Release and catch” catalytic systems

In this perspective article the “release and catch” catalytic system concept is discussed. A “release and catch” catalytic system is prepared by non-covalent immobilization of the catalytic moiety on a suitable support, but differently from the usual non-covalently supported catalyst, the catalytic moiety is released in solution over the course of the reaction and it is recaptured at the end of the reaction. Such a “catalyst- sponge like” or “boomerang” system allows one to combine the benefits of homogeneous and heterogeneous catalysis and can be applied to organometallic-based catalysts, organocatalysts and metal-based catalysts.

L-Prolina supportata su polistirene come catalizzatore eterogeneo nella reazione di condensazione aldolica “in the presence of water”