Supported Au Nanoparticles‐Catalyzed Regioselective Dehydrogenative Disilylation of Allenes by Dihydrosilane (original) (raw)
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Synthesis of bifunctional disiloxanes via subsequent hydrosilylation of alkenes and alkynes
Chemical Communications, 2021
Image used with the kind permission of Twinkl Educational Publishing. (c) Twinkl Ltd. All Rights Reserved. Synthesis of bifunctional disiloxanes via subsequent hydrosilylation of alkenes and alkynes The first protocol for the synthesis of unsymmetrical bifunctional 1,1,3,3-tetramethyldisiloxane derivatives via subsequent hydrosilylation of alkenes and alkynes is presented. The methodology described has vast functional group tolerance and is extremely efficient towards the formation of novel disiloxane-based building blocks.
Journal of the American Chemical Society, 2014
The mechanism of gold-catalyzed coupling of arenes with aryltrimethylsilanes has been investigated, employing an improved precatalyst (thtAuBr 3) to facilitate kinetic analysis. In combination with linear free-energy relationships, kinetic isotope effects, and stoichiometric experiments, the data support a mechanism involving an Au(I)/Au(III) redox cycle in which sequential electrophilic aromatic substitution of the arylsilane and the arene by Au(III) precedes productforming reductive elimination and subsequent cycle-closing reoxidation of the metal. Despite the fundamental mechanistic similarities between the two auration events, high selectivity is observed for heterocoupling (C−Si then C−H auration) over homocoupling of either the arylsilane or the arene (C−Si then C− Si, or C−H then C−H auration); this chemoselectivity originates from differences in the product-determining elementary steps of each electrophilic substitution. The turnover-limiting step of the reaction involves associative substitution en route to an arene π-complex. The ramifications of this insight for implementation of the methodology are discussed.
Hydrosilylation of 1-hexyne promoted by acetone solvated gold atoms derived catalysts
Journal of Organometallic Chemistry, 2005
Supported gold nanoparticles, prepared by deposition of acetone solvated Au atoms on supports as carbon and c-Al 2 O 3 , behave as valuable catalysts for the regioselective hydrosilylation of 1-hexyne with different silanes. The catalytic behaviour of gold-based systems is compared with the activity of supported platinum catalysts and a different affinity between the metals and the silanes is observed.
The Journal of Organic Chemistry, 1999
Umpolung of the carbon-sulfur bonds can be achieved by treatment of propargylic dithioacetals 1 with organocuprates. The organocopper intermediates 3 gave the corresponding allenyl thioethers 4 upon protonolysis. When alkyl halides were used, propargylic thioethers 5 were obtained exclusively. Transmetalation of organocopper intermediates 3 with ZnBr 2 followed by Pd(PPh 3) 4catalyzed coupling with vinylic or aryl halides afforded the corresponding allenyl thioethers 4. Either 4 or 5 reacted with Grignard reagents in the presence of NiCl 2 (dppf) to yield the corresponding allenes 9 or 10, respectively. The overall reaction can be considered to use 1 as allene-1,3-zwitterion synthons. The relative reactivities of a propargylic ether versus a propargylic dithioacetal toward an organocopper reagent were compared. The sulfur moiety apparently has higher reactivity toward the copper reagent.
Chemical Communications, 2010
General Information Unless otherwise noted, all reactions were performed in flame-dried or oven-dried glassware under argon atmosphere. Non-aqueous reagents were transferred using syringe techniques under argon atmosphere. Bulk grade hexanes, pentane and ethyl acetate (EtOAc) for chromatography were distilled prior to use. Tetrahydrofuran (THF), dimethylformamide (DMF), dichloromethane (DCM), acetonitrile (MeCN) and diethylether (Et 2 O) were obtained anhydrous by degassing with argon and then passing through activated alumina columns to remove water and oxygen. 1 Triethylamine (Et 3 N) and pyridine (C 5 H 5 N) were distilled from CaH 2 under argon immediately before use. Titanium isopropoxide (Ti(O i Pr) 4) and ethyl chloroformate (EtOCOCl) were distilled using a fractionating column at atmospheric pressure under argon immediately before use. Reactions were monitored by standard thin-layer chromatography (TLC) techniques using EMD silica gel 60 F 254 pre-coated plates (0.25 mm thickness). Developed TLC plates were visualized under UV light and/or by appropriate stains (p-anisaldehyde or cerric ammonium nitrate or potassium permanganate). Preparative TLC separations were performed using Merck silica gel 60 F 254 pre-coated plates (0.50 mm thick). Flash column chromatography was performed with Silica-P Flash Silica Gel (ultra-pure 40-63 μm) from Silicycle Chemical Division (Quebec QC, Canada).
Allene formation by gold catalyzed cross-coupling of masked carbenes and vinylidenes
Proceedings of the National Academy of Sciences, 2007
Addition of a sterically demanding cyclic (alkyl)(amino)carbene (CAAC) to AuCl(SMe 2) followed by treatment with [Et3Si(Tol)] ؉ [B(C6F5)4] ؊ in toluene affords the isolable [(CAAC)Au(2-toluene)] ؉ [B(C6F5)4] ؊ complex. This cationic Au(I) complex efficiently mediates the catalytic coupling of enamines and terminal alkynes to yield allenes and not propargyl amines as observed with other catalysts. Mono-, di-, and tri-substituted enamines can be used, as well as aryl-, alkyl-, and trimethylsilyl-substituted terminal alkynes. The reaction tolerates sterically hindered substrates and is diastereoselective. This general catalytic protocol directly couples two unsaturated carbon centers to form the three-carbon allenic core. The reaction most probably proceeds through an unprecedented ''carbene/vinylidene cross-coupling.'' catalysis ͉ enamines ͉ alkynes ͉ transition metal C arbon-carbon bond-forming reactions are at the heart of Author contributions: V.L. designed research; G.D.F. and S.K. performed research; B.D. contributed new reagents/analytic tools; and G.B. wrote the paper.
Tetrahedron, 2014
a b s t r a c t 1,1,3,3-Tetramethyldisiloxane (TMDS) is a highly reactive reducing reagent in the Au/TiO 2 -catalyzed hydrosilylation of carbonyl compounds relative to monohydrosilanes. The reduction of aldehydes or ketones with TMDS can be performed on many occasions at ambient conditions within short reaction times and at low loading levels of gold, whereas typical monohydrosilanes require excess heating and prolonged time for completion. The product yields are excellent, while almost stoichiometric amounts of carbonyl compounds and TMDS can be used. It is postulated that the enhanced reactivity of TMDS is attributed to the formation of a gold dihydride intermediate. This intermediate is also supported by the fact that double hydrosilylation of carbonyl compounds by TMDS is a negligible pathway.
Journal of Catalysis, 2020
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Journal of the American Chemical Society, 2013
The first highly efficient ligand-controlled regioand stereodivergent intermolecular hydrosilylations of internal alkynes have been disclosed. Cationic ruthenium complexes [Cp*Ru(MeCN) 3 ] + and [CpRu(MeCN) 3 ] + have been demonstrated to catalyze intermolecular hydrosilylations of silyl alkynes to form a range of vinyldisilanes with excellent but opposite regio-and stereoselectivity, with the former being α anti addition and the latter β syn addition. The use of a silyl masking group not only provides sufficient steric bulk for high selectivity but also leads to versatile product derivatizations toward a variety of useful building blocks. DFT calculations suggest that the reactions proceed by a mechanism that involves oxidative hydrometalation, isomerization, and reductive silyl migration. The energetics of the transition states and intermediates varies dramatically with the catalyst ligand (Cp* and Cp). Theoretical studies combined with experimental evidence confirm that steric effect plays a critical role in governing the regio-and stereoselectivity, and the interplay between the substituent in the alkyne (e.g., silyl group) and the ligand ultimately determines the observed remarkable regio-and stereodivergence.