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Relevant academic research and scientific papers

A recyclable and reusable K2PtCl4/Xphos-SO3Na/PEG-400/H2O system for highly regio- and stereoselective hydrosilylation of terminal alkynes

K2PtCl4/Xphos-SO3Na in a mixture of poly(ethylene glycol) (PEG-400) and water is shown to be a highly regio- and stereoselective catalyst for the hydrosilylation of terminal alkynes with hydrosilanes. The reaction could be conducted under mild conditions, yielding a variety of functionalized β-(E)-vinylsilanes in good to excellent yields with a total β-(E)-selectivity. The isolation of the products is readily performed by extraction with cyclohexane and more importantly, both expensive K2PtCl4 and Xphos-SO3Na in a PEG-400/H2O system could be easily recycled and reused at least eight times without any loss of catalytic activity.

Markovnikov Hydrosilylation of Alkynes with Tertiary Silanes Catalyzed by Dinuclear Cobalt Carbonyl Complexes with NHC Ligation

Metal-catalyzed hydrosilylation of alkynes is an ideal atom-economic method to prepare vinylsilanes that are useful reagents in the organic synthesis and silicone industry. Although great success has been made in the preparation of β-vinylsilanes by metal-catalyzed hydrosilylation reactions of alkynes, reported metal-catalyzed reactions for the synthesis of α-vinylsilanes suffer from narrow substrate scope and/or poor selectivity. Herein, we present selective Markovnikov hydrosilylation reactions of terminal alkynes with tertiary silanes using a dicobalt carbonyl N-heterocyclic carbene (NHC) complex [(IPr)2Co2(CO)6] (IPr = 1,3-di(2,6-diisopropylphenyl)imidazol-2-ylidene) as catalyst. This cobalt catalyst effects the hydrosilylation of both alkyl- and aryl-substituted terminal alkynes with a variety of tertiary silanes with good functional group compatibility, furnishing α-vinylsilanes with high yields and high α/β selectivity. Mechanistic study revealed that the stoichiometric reactions of [(IPr)2Co2(CO)6] with PhCCH and HSiEt3 can furnish the dinuclear cobalt alkyne and mononuclear cobalt silyl complexes [(IPr)(CO)2Co(μ-ν2:ν2-HCCPh)Co(CO)3], [(IPr)(CO)2Co(μ- ν2:ν2-HCCPh)Co(CO)2(IPr)], and [(IPr)Co(CO)3(SiEt3)], respectively. Both dicobalt bridging alkyne complexes can react with HSiEt3 to yield α-triethylsilyl styrene and effect the catalytic Markovnikov hydrosilylation reaction. However, the mono(NHC) dicobalt complex [(IPr)(CO)2Co(μ- ν2:ν2-HCCPh)Co(CO)3] exhibits higher catalytic activity over the di(NHC)-dicobalt complexes. The cobalt silyl complex [(IPr)Co(CO)3(SiEt3)] is ineffective in catalyzing the hydrosilylation reaction. Deuterium labeling experiments with PhCCD and DSiEt3 indicates the syn-addition nature of the hydrosilylation reaction. The absence of deuterium scrambling in the hydrosilylation products formed from the catalytic reaction of PhCCH with a mixture of DSiEt3 and HSi(OEt)3 hints that mononuclear cobalt species are less likely the in-cycle species. These observations, in addition to the evident of nonsymmetric Co2C2-butterfly core in the structure of [(IPr)(CO)2Co(μ- ν2:ν2-HCCPh)Co(CO)3], point out that mono(IPr)-dicobalt species are the genuine catalysts for the cobalt-catalyzed hydrosilylation reaction and that the high α selectivity of the catalytic system originates from the joint play of the dicobalt carbonyl species to coordinate alkynes in the Co(μ- ν2:ν2-HCCR′)Co mode and the steric demanding nature of IPr ligand.

Reaction of hydrosilanes with alkynes catalyzed by gold nanoparticles supported on TiO2

Gold nanoparticles supported on TiO2 (0.8-1.4 mol %) catalyze the β-(E) regioselective hydrosilylation of a variety of functionalized terminal alkynes with alkylhydrosilanes in 1,2-dichloroethane (70 °C). The product yields are excellent, and the reaction times relatively short, while almost equimolar amounts of alkynes and hydrosilanes can be used. Minor side-products in up to 35% relative yield of cis-oxidative (dehydrogenative) disilylation, an unprecedented reaction pathway, are formed in the cases of the less hindered hydrosilanes and alkynes. Triethoxysilane reacts faster and affords apart from β-(E) addition products, minor α-hydrosilylation regio-isomers in upto 15% relative yield. Internal alkynes are generally less reactive or even unreactive. It is proposed that cationic Au(I) species stabilized by the support are the reactive catalytic sites, forming in the presence of hydrosilanes either silyl-Au(III)-H (hydrosilylation pathway) or Au(III)-disilyl species (dehydrogenative disilylation pathway). Regarding the mechanism of hydrosilylation, kinetic experiments are in agreement with silyl carbometallation of the triple bond in the rate determining step of the reaction.

Single-Operation Synthesis of Vinylsilanes from Alkenes and Hydrosilanes with the Aid of Ru3(CO)12

Alkenes (RCH=CH2, where R = C6H5, p-CH3C6H4, p-CH3OC6H4, p-ClC6H4, 2-naphthyl, (CH3)3C, Me3SiO(CH3)2C, n-C4H9O, and Et3Si) with HSiEt3 with Ru3(CO)12 as a catalyst gave corresponding vinylsilanes (1, 6-13) without formation of simple addition products.Hydrosilanes such as HSiMe3, HSiEt2Me, HSiPhMe2, and HSi(OEt)3 also yielded vinylsilanes.Alkenes having a hydrogen atom at the allylic position (1-hexene, allylbenzene, 3-phenoxyprop-1-ene, vinylcyclohexane, β-methylstyrene, α-methylstyrene, 2-hexene) formed mixtures of vinylsilanes and allylsilanes.The ratio of vinylsilane 16 to allylsilane 17 decreased with an increase in temperature and with time.Substituted styrenes with a hydrosilane in the presence of 1-hexene gave vinylsilanes 1 and 6-8 in good yields based on the styrenes along with n-hexane.