1703-46-4Relevant academic research and scientific papers
O-functionalised NHC ligands for efficient nickel-catalysed c-o hydrosilylation
Albrecht, Martin,Bertini, Simone
, p. 483 - 488 (2020)
A series of C,O-bidentate chelating mesoionic carbene nickel(ii) complexes [Ni(NHC^PhO)2] (NHC = imidazolylidene or triazolylidene) were applied for hydrosilylation of carbonyl groups. The catalytic system is selective towards aldehyde reduction and tolerant to electron-donating and -withdrawing group substituents. Stoichiometric experiments in the presence of different silanes lends support to a metal-ligand cooperative activation of the Si-H bond. Catalytic performance of the nickel complexes is dependent on the triazolylidene substituents. Butyl-substituted triazolylidene ligands impart turnover numbers up to 7,400 and turnover frequencies of almost 30,000 h-1, identifying this complex as one of the best-performing nickel catalysts for hydrosilylation and demonstrating the outstanding potential of O-functionalised NHC ligands in combination with first-row transition metals.
Synthesis, characterization, and catalytic application in aldehyde hydrosilylation of half-sandwich nickel complexes bearing (κ1-: C)- A nd hemilabile (κ2-C, S)-thioether-functionalised NHC ligands
Ulm, Franck,Poblador-Bahamonde, Amalia I.,Choppin, Sabine,Bellemin-Laponnaz, Stéphane,Chetcuti, Michael J.,Achard, Thierry,Ritleng, Vincent
, p. 17134 - 17145 (2018)
Neutral nickel-N-heterocyclic carbene complexes, (κ1-C)-[NiCpBr{R-NHC-(CH2)2SR′}] [Cp = η5-C5H5; R-NHC-(CH2)2SR′ = 1-mesityl-3-[2-(tert-butylthio)ethyl]-(1a), 1-mesityl-3-[2-(phenylthio)ethyl]-(1b), 1-benzyl-3-[2-(tert-butylthio)ethyl]-(1c), 1-benzyl-3-[2-(phenylthio)ethyl]-imidazol-2-ylidene (1d)], which bear a N-bound thioether side arm, were prepared by the reaction of nickelocene with the corresponding imidazolium bromides [R-NHC-(CH2)2SR′·HBr] (a-d), via conventional or microwave heating. The 1H NMR spectra of the benzyl-substituted species 1c and 1d showed signals for diastereotopic NCH2CH2S protons at room temperature. However, structural studies established the absence of coordination of the sulphur atom in the solid state, and solvent DFT calculations showed that bromide displacement by sulphur is an unfavourable process (ΔG = +13.5 kcal mol-1 for 1d), thereby suggesting that the observed disatereotopicity is more likely due to significant steric congestion rather than to a possible C,S-chelation in solution. Treatment of these complexes with KPF6 in tetrahydrofuran (THF) led to bromide abstraction to afford the cationic complexes [NiCp{R-NHC-(CH2)2SR′}](PF6) (2a-c). Alternatively, 2a-c could also be prepared by the direct reaction of nickelocene with the corresponding imidazolium hexafluorophosphate salts [R-NHC-(CH2)2SR′·HPF6]. Inversely to the neutral species, whereas X-ray crystallography established C,S-chelation in the solid state, the 1H NMR spectra (CDCl3, CD2Cl2, or thf-d8) at room temperature showed no diastereotopic NCH2CH2S protons, thus suggesting the possible displacement of the sulphur atom by the respective solvents and/or very fast sulphur inversion. DFT calculations established a low energy inversion process in all cases (+9 ≤ ΔG? ≤ +13 kcal mol-1) as well as a favourable solvent coordination process (ΔG? ≈ +11 kcal mol-1; ΔG ≈-7 kcal mol-1) with a solvent such as THF, thus suggesting that sulphur inversion and/or solvent coordination can both account for the absence of diastereotopy at room temperature, depending on the solvent. While all complexes catalysed the hydrosilylation of benzaldehyde in the absence of any additive, the cationic C,S-chelated complexes 2 proved more active than the sterically constrained neutral species 1. In particular, 2c proved to be the most active pre-catalyst and its catalytic charge could be lowered down to 2 mol% with PhSiH3 as the hydrogen source.
β-cyclodextrin as inverse phase transfer catalyst on the electrocatalytic hydrogenation of organic compounds in water
Vilar, Márcio,Navarro, Marcelo
, p. 270 - 278 (2012)
The optimum conditions for the electrocatalytic hydrogenation (ECH) of benzaldehyde in water, using a nickel sacrificial anode (SA) (referred to as ECH-SA) and β-cyclodextrin (β-CyD) as inverse phase transfer catalyst (IPTC) were determined. Four parameters were investigated: the morphology of the nickel deposited on the cathode matrix (Cu, Fe, Ni or Fe/Ni alloy (64:36)) during a pre-electrolysis, the size of the CyD cavity, the concentration of β-CyD, the supporting electrolyte concentration and the current density applied. The results showed that a Ni matrix together with ultrasound pre-electrolysis treatment allowed a nanostructured nickel deposit on the cathode surface. Under the best electrolysis conditions (2.8 mmol dm -3 of β-CyD, 1.0 mol dm-3 of NH4Cl and a current density of 330 mA dm-2), the yield of benzyl alcohol (99%) was 27% higher than that obtained under the same conditions but in the absence of β-CyD. Taking into account the hydrophobic character of the β-CyD, the best conditions of the ECH-SA method were applied to the hydrogenation of a variety of organic substrates. Excellent yields and current efficiencies were obtained with arylbenzaldehydes and acetophenone. ECH-SA of styrene gave moderate yield and current efficiency, and the hydrogenation of a terminal non-conjugated olefin (safrole) was not efficient.
Sulfurated borohydride exchange resin: A novel reagent for selective reduction of aldehydes
Bandgar,Kamble
, p. 3037 - 3040 (2001)
Selective reduction of aldehydes is carried out by using sulfurated borohydride exchange resin as a novel reducing reagent. Other sensitive groups like F, Cl, Br, NO2, CN, OMe, ester and methylenedioxy remain intact under these reaction conditions. The isolation of pure products by simple filtration and evaporation is an important feature of this method.
Hydrosilylation of Carbonyl Compounds Catalyzed through a Lithiated Hydrazone Derivative
Raya-Barón, álvaro,O?a-Burgos, Pascual,Rodríguez-Diéguez, Antonio,Fernández, Ignacio
, p. 2682 - 2689 (2018)
A well-defined lithiated hydrazone derivative has been synthesized and fully characterized through various analytical platforms, including multinuclear (1H, 13C, 15N, 7Li) and two-dimensional NMR, high-resolution MS spectrometry, IR, and X-ray diffraction crystallography. It behaves as a binuclear species in the solid state and as a monomeric contact ion pair in solution. It has also been tested as a catalyst in hydrosilylation reactions, being the first lithium hydrazone reported to catalyze the full conversion of carbonyls of different nature into alcohols in short reaction times, at room temperature, and with catalyst loadings equal to or below 0.5 mol %. Kinetic studies have proven fractional order dependences with respect to ketone and silane and first order dependence in the case of the catalyst. The proposed reaction mechanism is characterized by the nucleophilic addition of the lithium hydrazonide to the silicon atom of the silane to give a five-coordinate silicon species.
Benzyltriethylammonium chloride-zinc-methanol: A novel system for selective reduction of aldehydes to alcohols
Kardile,Desai,Swami
, p. 2129 - 2131 (1999)
A selective reduction of aldehydes to alcohols using benzyltriethy lammoniun chloride - zinc - Methanol System is done.
Development of an indirect spectrophotometric method for determination of methamidophos insecticide in soil, water and vegetable samples
Shah, Jasmin,Jan, M. Rasul,Muhammad, Mian,Ara, Behisht,Ur Rehman, Ibadat
, p. 311 - 318 (2015)
A simple and rapid indirect spectrophotometric method for determination of methamidophos in water, soil and vegetable samples has been described. Methamidophos reacts with acid produced from p-dimethylaminobenzaldehyde (p-DMAB) as a result of Cannizaro's reaction. The resultant adduct undergoes condensation reaction in acidic medium forming a yellow colored product. Absorbance of the colored product was measured at 405 nm and pH 3 against a reagent blank. The Beer's law range is obeyed in the range 1-30 μg mL-1 with molar absorptivity of 2.8 ×103 L mol-1 cm-1. The limit of detection and quantification were found to be 0.20±0.03 and 0.60±0.04 μg mL-1 respectively. The proposed method was effectively applied for determination of methamidophos in various samples with percent recoveries in the range of 96±0.08 to 102±0.06%.
(Cyclopentadienyl)iron(II) complexes of N-heterocyclic carbenes bearing a malonate or imidate backbone: Synthesis, structure, and catalytic potential in hydrosilylation
Cesar, Vincent,Misal Castro, Luis C.,Dombray, Thomas,Sortais, Jean-Baptiste,Darcel, Christophe,Labat, Stephane,Miqueu, Karinne,Sotiropoulos, Jean-Marc,Brousses, Remy,Lugan, Noel,Lavigne, Guy
, p. 4643 - 4655 (2013)
The backbone-functionalized anionic carbenes maloNHC (1R; malonate backbone) and imidNHC (2; imidate backbone) were generated in situ from their respective zwitterionic precursors and treated with FeCp(CO)2I to afford the zwitterionic complexes {FeCp(CO)2(1R)} (3R; 59-84% yield), and {FeCp(CO)2(2)} (4; 77% yield), respectively. Methylation of the malonate complex 3Me takes place at one of the backbone oxygen atoms to give the cationic adduct [FeCp(CO) 2(1MeMe)](OTf) ([5Me](OTf); 96% yield), whereas methylation of 4 takes place at the imidate nitrogen atom to produce the cationic adduct [FeCp(CO)2(2Me)](OTf) ([6 Me](OTf); 84% yield). All of the complexes were characterized by NMR and IR in solution, while X-ray structure analyses were carried out for 3 Me, 4, and [6Me](OTf). In addition, a detailed experimental and theoretical investigation of the electron density within the archetypal zwitterionic complex 3Me was carried out. The observation of short intramolecular contacts between Cipso or Cortho of the mesityl groups of the carbene and the proximal carbonyl groups is rationalized in terms of a noncovalent "through space" π-π* interaction involving a two-electron delocalization of the occupied π(Cipso=Cortho) molecular orbital (MO) of the aryl ring into one vacant π*(C≡O) MO of the carbonyl ligand. A theoretical analysis carried out on dissymmetrical model complexes reveals that the magnitude of such an interaction is correlated with the donor properties of aryl group substituents. A catalyst screening of the above complexes in the hydrosilylation of benzaldehyde under visible light irradiation revealed a dramatic effect of the electronic donor properties of these carbenes on the performances of their complexes, with the more nucleophilic carbene 1 tBu- in the zwitterionic species 3tBu appearing as the most efficient. This complex shows good efficiency and excellent chemoselectivity in the hydrosilylation of various aldehydes bearing reactive functional groups. It is also moderately active in the hydrosilylation of a few ketone substrates and exhibits very good performance in the hydrosilylation of representative aldimines and ketimines.
Lipophilic M(α,α′-OC5H11)8phthalocyanines (M = H2 and Ni(II)): Synthesis, electronic structure, and their utility for highly efficient carbonyl reductions
Jiang, Yu,Li, Minzhi,Liang, Xu,Mack, John,Wildervanck, Martijn,Nyokong, Tebello,Qin, Mingfeng,Zhu, Weihua
, p. 18237 - 18246 (2015)
A lipophilic and electron-rich phthalocyanine (α,α′-n-OC5H11)8-H2Pc and its nickel(ii) complex (α,α′-n-OC5H11)8-Ni(ii)Pc have been synthesized and characterized. Detailed analyses of the electronic structure were carried out by spectroscopy, electrochemistry, spectroelectrochemistry, and TD-DFT calculations. A series of experiments demonstrate that the (α,α′-n-OC5H11)8-Ni(ii)Pc complex can be used as a catalyst for highly efficient carbonyl reductions.
Triazolylidene Iron(II) Piano-Stool Complexes: Synthesis and Catalytic Hydrosilylation of Carbonyl Compounds
Johnson, Chloe,Albrecht, Martin
, p. 2902 - 2913 (2017)
A new series of iron(II) piano stool complexes was synthesized that contain monodentate triazolylidene ligands with different aryl and alkyl substituents as well as an example of a C,N-chelating pyridine-substituted triazolylidene iron complex. The electronic and steric effect of wingtip modification was assessed by electrochemical, infrared spectroscopic, and X-ray diffraction analysis. All complexes were active in the catalytic hydrosilylation of aldehydes and ketones. The monodentate systems outperform the chelating triazolylidene analogue by far, reaching turnover frequencies TOFmax as high as 14400 h-1 at 0.1 mol % catalyst loading. Mechanistic investigations indicate a radical mechanism for the catalytic H-Si bond activation.
