Hydrosilylation Of Ketones Research Articles

Asymmetric hydrosilylation of ketones catalyzed by complexes formed from trans-diaminocyclohexane-based diamines and diethylzinc.

Chiral acyclic and macrocyclic amines derived from trans-1,2-diaminocyclohexane in complexes with diethylzinc efficiently catalyze asymmetric hydrosilylation of aryl–alkyl and aryl–aryl ketones with enantiomeric excess of the product up to 86 %. A trianglamine ligand with a cyclic structure or the presence of an additional coordinating group increases the enantioselectivity of the reaction, in comparison with catalysis by a simple acyclic N,N′-dibenzyl-1,2-diaminocyclohexane ligand. In addition, the effect of the asymmetric activation of the catalyst by a variety of alcohols and diols is studied.Graphical Electronic supplementary materialThe online version of this article (doi:10.1007/s00706-012-0754-0) contains supplementary material, which is available to authorized users.

ChemInform Abstract: Copper(II)‐Catalyzed Hydrosilylation of Ketones Using Chiral Dipyridylphosphane Ligands: Highly Enantioselective Synthesis of Valuable Alcohols.

AbstractThe new copper‐catalyzed asymmetric hydrosilylation system gives excellent enantioselectivities (up to 98% e.e.) and exceeds high turnover rates (up to 50 000 S/L molar ratio in 50 min reaction time).

ChemInform Abstract: Pd‐Catalyzed Selective Hydrosilylation of Aryl Ketones and Aldehydes.

AbstractIt is demonstrated that Pd(O‐Ac)2 is an efficient catalyst for the hydrosilylation of various aryl ketones and aldehydes in DMF.

Rhodium-Catalyzed Hydrosilylation of Ketones: Catalyst Development and Mechanistic Insights

The current status of rhodium-catalyzed hydrosilylation of ketones is reviewed, focusing on development milestones leading to state of the art chiral ligand systems and mechanistic understanding. Four ligand classes are discussed: phosphorus-, nitrogen-, mixed-donor ligand- as well as N-heterocyclic carbene-based ligand systems. Results relevant for a mechanistic understanding of the reaction are presented, starting from the initial investigations by Ojima, limitations of the first mechanistic picture leading to the Zheng-Chan mechanism, which was recently replaced by a silylene-based mechanism introduced by Hofmann and Gade.

Asymmetric Hydrosilane Reduction of Ketones Catalyzed by an Iridium Complex Bearing a Hydroxyamide‐Functionalized NHC Ligand

AbstractAn enantioselective hydrosilylation of prochiral ketones was achieved by using a catalytic amount of the readily accessible and air‐ and moisture‐stable iridium complex [IrCl(cod)(NHC)] at room temperature.

Copper-Catalyzed Enantioselective Hydro-silylation of Dialkyl and Aryl-Alkyl Ketones

Copper-Catalyzed Enantioselective Hydro-silylation of Dialkyl and Aryl-Alkyl Ketones

Trioxorhena(VII)carborane Anion and Its Methyl-Substituted Analogue: Synthesis, Structure, DFT, and Catalytic Studies

Synthesis and characterization of trioxorhena(VII)carborane [Bu4N][(η1-C2B9H11)ReO3] (1a) and its methyl-substituted analogue [Bu4N][(7,8-Me2-η1-C2B9H11)ReO3] (1b) are reported. The single-crystal X-ray structures of 1a and 1b display η1 coordination between Re and the carborane cage. Density functional theory computations at B3LYP/LANL2DZ (Gaussian 09 suite) level show that the strong π donor character of the oxo ligands results in a weak interaction between the d orbitals on Re and the π orbitals of the boron cage, the consequence of which is favoring η1 Re–B coordination. Complexes 1a and 1b exhibit reversible one-electron reduction in cyclic voltammetry experiments at E1/2 potentials of −1.83 and −1.88 V versus Cp2Fe/Cp2Fe+, respectively. Complex 1a catalyzes the hydrosilylation of aldehydes and ketones in excellent yields and with high tolerance to a variety of functional groups. Mechanistic investigation of the hydrosilylation reaction revealed potential involvement of multirhenium–boron cluster.

ChemInform Abstract: Selective Hydrosilylation of Ketones Catalyzed by in situ‐Generated Iron NHC Complexes.

AbstractThe Fe—NHC‐catalyzed hydrosilylation of a wide variety of aromatic and aliphatic ketones with PMHS proceeds smoothly to give the corresponding alcohols in high yields and excellent chemoselectivity.

ChemInform Abstract: Bu4N[Fe(CO)3(NO)]‐Catalyzed Hydrosilylation of Aldehydes and Ketones.

The nucleophilic Fe complex Bu4N[Fe(CO)3(NO)] (TBAFe) has been used as a highly active catalyst for the mild hydrosilylation of a variety of functionalized aldehydes and ketones using inexpensive PMHS as stoichiometric reductant. The corresponding alcohols were obtained in good-to-excellent yields at low catalyst loadings of only 1 mol-% and reaction temperatures of 30–50 °C.

P/S ligands derived from carbohydrates in Rh-catalyzed hydrosilylation of ketones

Reported is the synthesis of a number of diastereomerically pure cationic Rh(I)-complexes I starting from phosphinite thioglycosides. These complexes were used in the asymmetric hydrosilylation of prochiral ketones. The reactivity and enantioselectivity of the reaction was shown to be dependent on the pyranose ring, the substituent at the sulfur atom, the hydroxylic protective groups and most significantly on the alkene co-ligand.

Catalyst development for organocatalytic hydrosilylation of aromatic ketones and ketimines

A new family of Lewis basic 2-pyridyl oxazolines have been developed, which can act as efficient organocatalysts for the enantioselective reduction of prochiral aromatic ketones and ketimines with trichlorosilane, a readily available and inexpensive reagent. 1-Isoquinolyl oxazoline, derived from mandelic acid, was identified as the most efficient catalyst of the series, capable of delivering high enantioselectivities in the reduction of both ketones (up to 94% ee) and ketimines (up to 89% ee).

Progress in Asymmetric Hydrosilylation of Ketones by Non-precious Metal Catalyst

As important intermediates for the development of biologically active molecules and fragrance etc., chiral secon- dary alcohols are synthesized through asymmetric hydrogenation. Recently, the asymmetric hydrosilylation process has been attracted because of its mild reaction conditions as well as inexpensive and safer reagent system. In this paper, some informa- tion about the recent development of the catalysts of the non-precious metal (Zn, Cu and so on) for asymmetric hydrosilylation reaction of prochiral ketones is briefly reviewed. Keywords asymmetric hydrosilylation; non-precious metal catalyst; chiral alcohol; prochiral ketone; progress

Stereospecific synthesis and catalytic activity of l-histidylidene metal complexes

We report on the synthesis, metal coordination, and catalytic impact of histidylidene, a histidine-derived N-heterocyclic carbene (NHC) ligand. The histidinium salt 3, comprising methyl substituents at both heterocyclic nitrogens and protected at the C- and N-terminus of the amino acid, was rhodated and iridated by a transmetallation protocol using Ag(2)O. Ambient temperature and short reaction times were pivotal for full retention of configuration at the α-carbon. The stereospecificity of the reaction was conveniently probed by (31)P NMR spectroscopy after transmetallation with rhodium(I) and coordination of enantiopure (S)-Ph-binepine. The histidylidene rhodium complexes are highly efficient catalysts for the mild hydrosilylation of ketones. For the cationic complexes [Rh(cod)(histidylidene)(phosphine)](+), lowering the temperature shifted the rate-limiting step of the catalytic reaction to an earlier stage that is not enantioselective. Hence the asymmetric induction-which is governed by the chiral phosphine-did not improve at low temperature.

Origins of enantioselectivity in the chiral diphosphine-ligated CuH-catalyzed asymmetric hydrosilylation of ketones

Computational investigations on the asymmetric hydrosilylation of acetophenone over ligated CuH catalysts were performed with the DFT method. The calculations predict that the catalytic reaction involves two steps: (1) CuH addition to the carbonyl group via a four-membered transition state (TS) with the formation of copper-alkoxide intermediates; (2) regeneration of the ligated CuH catalyst by an external SiH(4) through a metathesis process to yield the corresponding silyl ether. The calculations in the chiral diphosphine-ligated CuH systems suggest that the metathesis process is the rate-determining step (RDS). The CuH addition step is vital for the distribution of the racemic products and therefore represents the stereo-controlling step (SCT). In this step, the greater steric hindrance between the aromatic rings of the ligands and the substrate is identified as the major factor for enantioselectivity. The corresponding TS in the face-to-face mode, suffering less steric hindrance, is more stable than its analogue in the edge-to-face mode. The enantioselectivities are calculated to be related not only to the P-Cu-P bite angles in the stereo-controlling TSs, but also to the substituents at the P-aryl rings of the chiral ligands. In short, a larger P-Cu-P bite angle and suitably modified P-aryl rings together are necessary to achieve excellent ee values.

Highly efficient and convenient asymmetric hydrosilylation of ketones catalyzed with zinc Schiff base complexes

Several chiral Schiff base ligands derived from α-amino acids were prepared, and zinc complexes with these chiral Schiff base ligands prepared were tested for the catalytic asymmetric hydrosilylation of ketones, and the results showed that excellent ee values were obtained, which are the prominent examples of catalytic asymmetric hydrosilylation of ketones catalyzed with zinc complexes in the presence of readily available and inexpensive α-amino acids based Schiff base ligands.

Enantioselective Zinc‐Catalyzed Hydrosilylation of Ketones using Pybox or Pybim Ligands

The combination of ZnEt(2) and chiral pyridinebisoxazoline (pybox) or pyridinebisimidazoline (pybim) ligands catalyzed the asymmetric hydrosilylation of aryl, alkyl, cyclic, heterocyclic, and aliphatic ketones. Under mild conditions, high yields and good enantioselectivities were achieved. ESI measurements allowed for the characterization of the active catalyst.

Rhodium(I) complex catalyst immobilized on terpolymers of N‐vinylpyrrolidinone and 1‐vinylimidazole

AbstractThe hydrosilylation of cyclohexanone and acetone with triethysilane and diphenysilane catalyzed by polymer‐supported Rh(I) complex has been investigated. Two terpolymers of styrene, divinylbenzene, and 1‐vinylimidazole (S/DVB/VI) or N‐vinylpyrrolidinone (S/DVB/NVP) were used as the catalysts supports. Physical characterization of these materials has involved the measurements of the structural parameters in the dry and swollen states by DSC, the nitrogen BET adsorption method and inverse steric exclusion chromatography ISEC. From these results it can be concluded that the original polymer structure has been changed during the complex attachment giving rise to materials of higher porosity. X‐ray photoelectron spectroscopy XPS, IR, and AAS spectroscopy were used to characterization of heterogeneous complexes before and after use. The effect of the morphology of the support on the catalytic properties of the polymer‐supported Rh(I) species was tested in the hydrosilylation of ketones and correlated with the reaction mechanism. It was demonstrated that the high selectivity of homogeneous rhodium complex toward the silyl ethers can be partially reversed to the dehydrogenative silylation products by a proper choice of polymer support with favorable microporous structure. Recycling tests demonstrated high stability of the supported catalysts during prolonged use. The constant selectivity of the supported catalysts demonstrated during recycling experiments showed that they could be useful for practical application. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Copper(II)‐Catalyzed Hydrosilylation of Ketones Using Chiral Dipyridylphosphane Ligands: Highly Enantioselective Synthesis of Valuable Alcohols

In the presence of PhSiH(3) as the reductant, the combination of enantiomeric dipyridylphosphane ligands and Cu(OAc)(2)·H(2)O, which is an easy-to-handle and inexpensive copper salt, led to a remarkably practical and versatile chiral catalyst system. The stereoselective formation of a selection of synthetically interesting β-, γ- or δ-halo alcohols bearing high degrees of enantiopurity (up to 99.9% enantiomeric excess (ee)) was realized with a substrate-to-ligand molar ratio (S/L) of up to 10,000. The present protocol also allowed the hydrosilylation of a diverse spectrum of alkyl aryl ketones with excellent enantioselectivities (up to 98% ee) and exceedingly high turn-over rates (up to 50,000 S/L molar ratio in 50 min reaction time) in air, under very mild conditions, which offers great opportunities for the preparation of various physiologically active targets. The synthetic utility of the chiral products obtained was highlighted by the efficient conversion of optically enriched β-halo alcohols into the corresponding styrene oxide, β-amino alcohol, and β-azido alcohol, respectively.

Pd-catalyzed selective hydrosilylation of aryl ketones and aldehydes

Pd salts in combination with triethylsilane as hydride source and DMF as solvent has been found to be excellent catalytic combination that selectively reduces aryl ketones and aldehydes under mild conditions to afford triethylsilyloxy compounds in excellent yields. Product selectivity to the respective benzyl alcohols can however be achieved when the reaction was performed in DMF/H2O (4:1) as solvent system.

The Hieber Anion [Fe(CO)3(NO)

(A) Allylic Substitutions with C-Nucleophiles: Building on early work by Roustan et al. and Xu et al. an efficient allylic substitution using carbon-centered nucleophiles was developed. In a first account the beneficial effects of Ph3P were shown. ipso Substitution was observed and a σ-allyl-iron intermediate was suggested.4a A second-generation protocol allowed for the selective formation of either linear or branched products based on the choice of ligand. The t-Bu-substituted NHC ligand gave access to branched selectively, whereas the aryl-substituted NHC ligand gave access to the linear product preferentially. (B) Allylic Substitutions with N-Nucleophiles: The allylic amination of allyl carbonates could be carried out by using catalytic amounts of Bu4N[Fe(CO)3(NO)]. The addition of piperidine HCl proved to be crucial for the reaction to take place when less substituted carbonates were used. ipso Substitution and retention of the stereochemistry was observed in all cases. (C) Allylic Substitutions with S-Nucleophiles: The allylic sulfonation of allyl carbonates was reported using catalytic amounts of Bu4N[Fe(CO)3(NO)] and sodium sulfinates as nucleophiles. Consistent with previous observations ipso substitution and retention of the stereochemistry was observed. Recently an allylic sulfenylation has been reported. (D) Allylic Substitutions with O-Nucleophiles: The O-allylation of phenols was reported using allyl carbonates, which upon treatment with catalytic amounts of Ph3P and Bu4N[Fe(CO)3(NO)] forms allyl phenyl ethers. Interestingly, this reaction was suggested to proceed via a π-allyl mechanism, based on the regiochemical outcome of this reaction. (E) C1-C16 Fragment of Ionomycin: Kocienski and co-workers employed Bu 4N[Fe(CO)3(NO)] in the preparation of the C1-C16 fragment of the polyketide natural product ionomycin. In a stoichiometric reaction of the enantiopure mesylate with the Hieber anion a configurationally stable iron allyl complex is formed as a 4:1 mixture of diastereoisomers. Separation via crystallization and subsequent reaction with an organocuprate gives rise to the desired advanced intermediate with retention of the stereochemistry based on the mesylate. (F) Carbonylation of Primary and Secondary Alkyl Halides: Davies et al. reported the carbonylation of alkyl halides with stoichiometric amounts of Bu4N[Fe(CO)3(NO)] in the presence of a carbon monoxide atmosphere. Initial alkylation takes place at the iron nucleophile followed by CO insertion to give an iron acyl species which upon substitution by methoxide gives the product.10 It has to be noted that potential β-hydride elimination does not take place. When MeOH was replaced by the hydride source NaHB(OMe)3 the corresponding alcohols were obtained. (G) Transesterification: The Bu4N[Fe(CO)3(NO)] catalyzed transesterification was recently reported. Alcohols were readily acylated using vinyl acetate in nhexane at elevated temperature. Further, molecular sieves had to be employed as the reaction exhibited a severe sensitivity to towards moisture. Phenyl esters or activated methyl esters also proved to be good acyl donors in this reaction. Mechanistically the reaction proceeds via a putative iron acyl intermediate. (H) Thioesterification: The transesterification was developed into a protocol for the preparation of thioesters from p-chlorophenyl esters in the presence of Bu4N[Fe(CO)3(NO)]. In the course of this study this reaction was applied to a native chemical ligation affording dipeptides via intermediate thioesters. (I) Hydrosilylation of Aldehydes and Ketones: Treatment of the appropriate carbonyl compounds with polymethylhydrosiloxane (PMHS), a hydride source, in the presence of as little as 1 mol% Bu4N[Fe(CO) 3(NO)] results in excellent yields of the alcohols after basic workup. Inclusion of the phosphine ligand PCy3 had a profound effect on the yield.