Catalytic Hydrosilylation Reaction Of Terminal Alkynes With Tertiary Silanes By A Cobalt(0) Carbonyl Complex With NHC Ligation

Transition-metal-catalyzed hydrosilylation of alkynes is an efficient method to access vinylsilanes that are useful synthetic intermediates in organic synthesis due to their versatility and low toxicity.Regio-and stereo-selective hydrosilylation has always been a challenging problem.Compared with various well established catalytic systems for hydrosilylation of terminal alkynes towardsβ-（E）-andβ-（Z）-vinylsilanes,the synthetic ways to geminalα-vinylsilanes（Markovnikov addition）are still rare,especially with commercially available tertiary silanes.Only a few examples so far are accessible toα-vinylsilanes with tertiary silanes,involving noble transition metals Ru,Rh,Ir and Pt.For example,ruthenium catalyst[（Cp*）Ru（Me CN）₃][PF₆]could catalyze the Markovnikov hydrosilylation of alkyl substituted alkynes,but examples of aryl substituted terminal alkynes were rare and the hydrosilanes were limited.The iridium catalyst[Ir₂（μ-Cl）₂（COD）₂]could only catalyze Markovnikov hydrosilylation of alkyl substituted terminal alkynes with HSi（OTMS）₃.Although bis-NHC rhodium catalyst[Rh（CF₃COO）₂（bis-NHC）][BF₄]and ligand-free Pt₃ cluster could catalyze Markovnikov hydrosilylation of aryl substituted terminal alkynes,but substrate scope is limited and selectivity was poor.Markovnikov hydrosilylation of various tertiary silanes with both terminal alkyl and aryl substituted alkynes has hardly been reported.Based on cobalt complex[（IPr）₂Co₂（CO）₆]previously reported by our group,we have developed the catalytic system for Markovnikov hydrosilylation of terminal alkynes and tertiary silanes.Phenylacetylene and triethylsilane were used as reaction substrates to screen the reaction temperature,reaction time,catalyst ligand,solvent and catalyst loading.The optimal conditions were achieved when 5 mol%[（IPr）₂Co₂（CO）₆]was used and the catalytic reaction was heated at 60℃in tetrahydrofuran for 5 hours.Under the optimal conditions,the reaction givesα-vinylsilanes with 98%GC yield and 90%isolated yield.The substrate scope of this reaction for different arylalkynes,alkylalkynes and silanes under optimal conditions had been investigated,and finally obtained a series ofα-vinylsilanes（α/β-（E）≥10/1）.All the hydrosilylation products in this paper have been characterized by NMR spectroscopy,part of them have been characterized by mass spectrometry,infrared spectroscopy,and single crystal X-ray diffraction.To summarize,this catalytic reaction gave Markovnikov hydrosilylation products and shows wide substrate scope to both terminal alkynes and tertiary silanes.