Search results for "element"

Catalytic Carbonylative Double Cyclization of 2-(3-Hydroxy-1-yn-1-yl)phenols in Ionic Liquids Leading to Furobenzofuranone Derivatives

2019

A catalytic carbonylative double cyclization method for the synthesis of furo[3,4-b]benzofuran-1(3H)-ones is reported. It is based on the reaction between readily available 2-(3-hydroxy-1-yn-1-yl)phenols, CO, and oxygen carried out in the presence of catalytic amounts of PdI2 (1 mol %) in conjunction with KI (20 mol %) and 2 equiv of diisopropylethylamine at 80 degrees C for 24 h under 30 atm of a 1:4 mixture of CO-air. Interestingly, the process was not selective when carried out in classical organic non-nucleophilic solvents (such as MeCN or DME), leading to a mixture of the benzofurofuranone derivative and the benzofuran ensuing from simple cycloisomerization, whereas it turned out chemo…

Copper-Catalyzed Aerobic Oxidative Alkynylation of 3,4-Dihydroquinoxalin-2-ones

2019

Herein, we described a ligand-free copper-catalyzed aerobic oxidative functionalization of 3,4-dihydroquinoxalin-2(1H)-ones with terminal alkynes using visible-light and oxygen as terminal oxidant to give 3-ethynyl-3,4-dihydroquinoxalin-2(1H)-one, cyclic propargylic amines, in moderate to good yields. Moreover, we demonstrate the versatility of the 3-ethynyl-3,4-dihydroquinoxalin-2(1H)-ones obtained by preparing several 3,4-dihydroquinoxalin-2-one derivatives.

Iron( ii ) and cobalt( ii ) complexes based on anionic phenanthroline-imidazolate ligands: reversible single-crystal-to-single-crystal transformations

2018

A series of low-spin FeII and CoII complexes based on phenanthroline-imidazolate (PIMP) ligands are reported. The FeII complex (H9O4)[Fe(PIMP)3]·(C4H10O)2(H2O) (1a) shows reversible crystalline phase transformations to afford two new phases (H9O4)[Fe(PIMP)3]·(H2O) (1b) and (H9O4)[Fe(PIMP)3]·(C8H18O)(C4H10O)(H2O) (1c) by release of diethyl ether and absorption of diethyl/dibutyl ether, respectively. This reversible uptake/release of solvent molecules is a clear example of single-crystal-to-single-crystal transformation involving a discrete metal complex. On the other hand, the corresponding CoII complex (H9O4)[Co(PIMP)3]·(C4H10O)2(H2O)2 (2) does not exhibit similar phase transformations. In …

Electrosynthesis and X‐ray Crystallographic Structure of Zn II meso ‐Triaryltriphenylphosphonium Porphyrin and Structural Comparison with Mg II meso …

2018

The hetero-cubane structures of the heavy alkali metal tert-amyloxides [MOCMe2Et]4 (M = K, Rb, Cs)

2018

A series of alkali metal (Li–Cs) alkoxides of tert-pentanol (1,1-dimethylpropan-1-ol) have been prepared by reaction of the corresponding metal with the alcohol in n-hexane or n-heptane. The compounds were purified by vacuum sublimation and crystallised in n-hexane to produce crystals suitable for single-crystal X-ray diffraction studies. The structures of the potassium, rubidium, and caesium compounds revealed tetrameric units with additional intra- and intermolecular interactions between the metal atom and alkoxide methyl groups, increasing with the size of the metal involved.

Comparative hydroamination of aniline and substituted anilines with styrene on different zeolites, triflate based catalysts and their physical mixtur…

2014

Abstract Catalytic performances of different zeolites (Beta and mordenites), scandium triflate based catalysts, mesoporous UVM-7 encapsulated scandium triflate and physical mixtures prepared under ultrasound irradiation were evaluated in the hydroamination of aniline and substituted anilines with styrene. The performances of these catalysts were controlled by the type of acidity and strength. Thus, the conversion was mainly controlled by the strength of the acid sites and their accessibility, while the selectivity appeared to be controlled by the Lewis/Bronsted type of acidity. Lewis acid catalysts directed the reactions mainly to the formation of the Markovnikov adducts while Bronsted acid…

Kinetic and Electrochemical Studies of the Oxidative Addition of Demanding Organic Halides to Pd(0): the Efficiency of Polyphosphane Ligands in Low P…

2013

International audience; Oxidative addition (OA) of organic halides to palladium(0) species is a fundamental reaction step which initiates the C–C bond formation catalytic processes typical of Pd(0)/Pd(II) chemistry. The use of structurally congested polyphosphane ligands in palladium-catalyzed C–C bond formation has generated very high turnover numbers (TONs) in topical reactions such as Heck, Suzuki, Sonogashira couplings, and direct sp2C–H functionalization. Herein, the OA of aryl bromides to Pd(0) complexes stabilized by ferrocenylpolyphosphane ligands L1 (tetraphosphane), L2 (triphosphane), and L3 (diphosphane) is considered. The investigation of kinetic constants for the addition of Ph…

Highly Anisotropic Rhenium(IV) Complexes: New Examples of Mononuclear Single-Molecule Magnets

2013

The rhenium(IV) complex (NBu4)2[ReBr4(ox)] (1) (ox = oxalate and NBu4(+) = tetra-n-butylammonium cation) has been prepared and its crystal structure determined by X-ray diffraction. The structure is made up of discrete [ReBr4(ox)](2-) anions and bulky NBu4(+) cations. Each [ReBr4(ox)](2-) anion is surrounded by six NBu4(+) cations, which preclude any significant intermolecular contact between the anionic entities, the shortest rhenium···rhenium distance being 9.373(1) Å. Variable temperature dc and ac magnetic susceptibility measurements and field-dependent magnetization experiments on polycrystalline samples of 1 reveal the occurrence of highly anisotropic magnetically isolated Re(IV) cent…

Enantiomeric Resolution of Asymmetric-Carbon-Free Binuclear Double-Stranded Cobalt(III) Helicates and Their Application as Catalysts in Asymmetric Re…

2018

A series of double-stranded binuclear helicates [Co2(H1)2]4+, [Co2(H2)2]4+, and [Co2(H3)2]4+, derived from monodeprotonated bis-pyridyl hydrazine-based ligands of H21, H22, and H23 with one, two, and three -CH2 spacers, were obtained. These asymmetric-carbon-free racemic helicates were separated into their ΔΔ and ΛΛ enantiomers. The resolved helicates were examined for the first time as enantioselective catalysts in asymmetric benzoylation and nitroaldol reactions.

Cathodic Corrosion of Metal Electrodes—How to Prevent It in Electroorganic Synthesis

2021

The critical aspects of the corrosion of metal electrodes in cathodic reductions are covered. We discuss the involved mechanisms including alloying with alkali metals, cathodic etching in aqueous and aprotic media, and formation of metal hydrides and organometallics. Successful approaches that have been implemented to suppress cathodic corrosion are reviewed. We present several examples from electroorganic synthesis where the clever use of alloys instead of soft neat heavy metals and the application of protective cationic additives have allowed to successfully exploit these materials as cathodes. Because of the high overpotential for the hydrogen evolution reaction, such cathodes can contri…