Search results for "Homogeneous catalysi"

Facile Synthesis and Self‐Assembly of Zinc (2‐Diethoxyphosphorylethynyl)porphyrins

2019

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

2015

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 …

Lanthanide bis(trifluoromethylsulfonyl)amides vs. trifluoromethylsulfonates as catalysts for Friedel–Crafts acylations

2002

Abstract The use of catalytic amounts: 1 mol% or less of perfluoroalkyl lanthanide salts as homogeneous catalysts for Friedel–Crafts acylations in non-hazardous solvents is thereafter investigated. Lanthanide bis(trifluoromethylsulfonyl)amides are better catalysts than the triflate analogues towards the acetylation of activated aromatic rings.

Group 3 and 4 metal alkyl and hydrido complexes containing a linked amido-cyclopentadienyl ligand: “constrained geometry” polymerization catalysts fo…

2002

Abstract In order to understand the nature of the putative cationic 12-electron species [M(η 5 :η 1 -C 5 R 4 SiMe 2 NR′)R″] + of titanium catalysts supported by a linked amido-cyclopentadienyl ligand, several derivatives with different cyclopentadienyl C 5 R 4 and amido substituents R′ were studied systematically. The use of tridentate variants (C 5 R 4 SiMe 2 NCH 2 CH 2 X) 2− (C 5 R 4 =C 5 Me 4 , C 5 H 4 , C 5 H 3 t Bu ; X=OMe, SMe, NMe 2 ) allowed the NMR spectroscopic observation of the titanium benzyl cations [Ti(η 5 :η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 X)(CH 2 Ph)] + . Isoelectronic neutral rare earth metal complexes [Ln(η 5 :η 1 -C 5 R 4 SiMe 2 NR′)R″] can be expected to be active for pol…

Efficient Anodic and Direct Phenol-Arene C,C Cross-Coupling: The Benign Role of Water or Methanol

2012

C,C cross-coupling reactions for the synthesis of nonsymmetrical biaryls represent one of the most significant transformations in contemporary organic chemistry. A variety of useful synthetic methods have been developed in recent decades, since nonsymmetrical biaryls play an evident role in natural product synthesis, as ligand systems in homogeneous catalysis and materials science. Transformation of simple arenes by direct C,H activation belongs to the cutting-edge strategies for creating biaryls; in particular the 2-fold C,H activation is of significant interest. However, in most examples very costly noble metal catalysts, ligand systems, and significant amount of waste-producing oxidants …

Di- and Tetrairon(III) μ-Oxido Complexes of an N3S-Donor Ligand: Catalyst Precursors for Alkene Oxidations

2019

The new di- and tetranuclear Fe(III) μ-oxido complexes [Fe 4 (μ-O) 4 (PTEBIA) 4 ](CF 3 SO 3 ) 4 (CH 3 CN) 2 ] (1a), [Fe 2 (μ-O)Cl 2 (PTEBIA) 2 ](CF 3 SO 3 ) 2 (1b), and [Fe 2 (μ-O)(HCOO) 2 (PTEBIA) 2 ](ClO 4 ) 2 (MeOH) (2) were prepared from the sulfur-containing ligand (2-((2,4-dimethylphenyl)thio)-N,N-bis ((1-methyl-benzimidazol-2-yl)methyl)ethanamine (PTEBIA). The tetrairon complex 1a features four μ-oxido bridges, while in dinuclear 1b, the sulfur moiety of the ligand occupies one of the six coordination sites of each Fe(III) ion with a long Fe-S distance of 2.814(6) A. In 2, two Fe(III) centers are bridged by one oxido and two formate units, the latter likely formed by methanol oxidati…

Highly Robust but Surface‐Active: An N‐Heterocyclic Carbene‐Stabilized Au 25 Nanocluster

2019

Surface organic ligands play a critical role in stabilizing atomically precise metal nanoclusters in solutions. However, it is still challenging to prepare highly robust ligated metal nanoclusters that are surface-active for liquid-phase catalysis without any pre-treatment. Now, an N-heterocyclic carbene-stabilized Au25 nanocluster with high thermal and air stabilities is presented as a homogenous catalyst for cycloisomerization of alkynyl amines to indoles. The nanocluster, characterized as [Au25 (i Pr2 -bimy)10 Br7 ]2+ (i Pr2 -bimy=1,3-diisopropylbenzimidazolin-2-ylidene) (1), was synthesized by direct reduction of AuSMe2 Cl and i Pr2 -bimyAuBr with NaBH4 in one pot. X-ray crystallization…

Highly Robust but Surface-Active: N-Heterocyclic Carbene-Stabilized Au25 Nanocluster as a Homogeneous Catalyst

2019

<div> <div> <div> <p>Surface organic ligands play a critical role in stabilizing atomically precise metal nanoclusters in solutions. However, it is still challenging to prepare highly robust ligated metal nanoclusters that are surface-active for liquid-phase catalysis without any pre-treatment. Herein, we report a novel N-heterocyclic carbine-stabilized Au25 nanocluster with high thermal and air stabilities as a homogenous catalyst for cycloisomerization of alkynyl amines to indoles. The nanocluster, characterized as [Au25(iPr2-bimy)10Br7]2+ (iPr2-bimy=diisopropyl-benzilidazolium) (1), was synthesized by direct reduction of AuSMe2Cl and iPr2- bimyAuBr with NaBH4 in o…

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

2016

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.

Spin state, electronic structure and bonding on C-scorpionate [Fe(II)Cl2(tpm)] catalyst: An experimental and computational study

2020

Abstract The Fe(II) spin state in the condensed phase of [Fe(II)Cl2(tpm)] (tpm = [tris(pyrazol-1-yl)methane]; 1) catalyst has been determined through a combined experimental and theoretical investigation of X-Ray Absorption Spectroscopy (XAS) at the FeL2,3-edges and NK-edge. Results indicated that in this phase a mixed singlet/triplet state is plausible. These results have been compared with the already know Fe singlet spin state of the same complex in water solution. A detailed analysis of the electronic structure and bonding mechanism of the catalyst showed that the preference for the low-spin diamagnetic ground state, strongly depends upon the ligands, the bulk solvent and the interactio…