1703-46-4Relevant articles and documents
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.
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.
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.
(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.
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.
Hydrogenation of Esters by Manganese Catalysts
Li, Fu,Li, Xiao-Gen,Xiao, Li-Jun,Xie, Jian-Hua,Xu, Yue,Zhou, Qi-Lin
, (2022/01/13)
The hydrogenation of esters catalyzed by a manganese complex of phosphine-aminopyridine ligand was developed. Using this protocol, a variety of (hetero)aromatic and aliphatic carboxylates including biomass-derived esters and lactones were hydrogenated to primary alcohols with 63–98% yields. The manganese catalyst was found to be active for the hydrogenation of methyl benzoate, providing benzyl alcohol with turnover numbers (TON) as high as 45,000. Investigation of catalyst intermediates indicated that the amido manganese complex was the active catalyst species for the reaction. (Figure presented.).
KB3H8: An environment-friendly reagent for the selective reduction of aldehydes and ketones to alcohols
Li, Xinying,Mi, Tongge,Guo, Wenjing,Ruan, Zhongrui,Guo, Yu,Ma, Yan-Na,Chen, Xuenian
supporting information, p. 12776 - 12779 (2021/12/10)
Selective reduction of aldehydes and ketones to their corresponding alcohols with KB3H8, an air- and moisture-stable, nontoxic, and easy-to-handle reagent, in water and THF has been explored under an air atmosphere for the first time. Control experiments illustrated the good selectivity of KB3H8 over NaBH4 for the reduction of 4-acetylbenzaldehyde and aromatic keto esters. This journal is
PHOTOPROXIMITY PROFILING OF PROTEIN-PROTEIN INTERACTIONS IN CELLS
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Page/Page column 114; 123, (2021/04/01)
Photoactive probes and probe systems for detecting biological interactions are described. The photoactive probes include probes that combine both photocleavable and photoreactive moieties. The photoactive probe systems can include a first probe comprising a photocatalytic group and a second probe comprising a group that can act as a substrate for the reaction catalyzed by the photocatalytic group. The probes and probe systems can also include groups that can specifically bind to a binding partner on a biological entity of interest and a detectable group or a precursor thereof. The probes and probe systems can detect spatiotemporal interactions of proteins or cells. In some embodiments, the interactions can be detected in live cells. Also described are methods of detecting the biological interactions.
