Mechanism Study On The Alkyne Hydrostannylation Reaction Catalyzed By Hetermobimetallic（NHC）Cu-[M_CO]([M_CO]=Mn（CO）₅,FeCp（CO）₂) Catalysts

Alkyne hydrofunctionalization is a highly atom-economical method in hydrocarbon functionalization.Vinylstannanes,produced from the alkyne hydrostannylation reactions,are of great significance in synthetic chemistry.These vinylstannanes facilitate a lot of important reactions to happen,and they are important intermediates due to their high chemical reactivity.The major challenge of the alkyne hydrofunctionalization is the control of product selectivity.The development of highly efficient regioselectivity and stereoselectivity methods is an important area for the preparation of vinylstannanes.The experimental results showed that the selectivity of alkyne hydrostannylation can be tuned by adjusting the two different metal in heterobimetallic catalysts.In this work,the detailed reaction mechanisms of two distinct Sn-H bond activation modes catalyzed by（NHC）Cu-[M_CO]([M_CO]=Mn（CO）₅,FeCp（CO）₂,Cp=C₅H₅)heterobimetallic catalysts（abbreviated as[Cu/Mn]and[Cu/Fe]）are investigated.The reasons of different product selectivity were explained.The similarities and differences of two catalytic mechanism were compared.Geometry optimizations,frequency calculations,single point energy corrections of reactants,transition states,intermediates and products,as well as intrinsic reaction coordinates（IRC）from transition states were a ll performed using Gaussian 09 package.This paper mainly includes the following three parts:1.The alkyne hydrostannylation catalyzed by[Cu/Mn]heterobimetallic catalyst contains three steps:Sn-H bond activation,alkyne insertion,and vinylstannanes formation.Sn-H bond activation is essential in the selectivity process for the product selectivity and the alkyne insertion process is the rate-determining step.In[Cu/Mn]catalytic process,the Sn-H bond is divided into（CH₃）₃Sn-Mn（CO）₅ and MeCuH.Alkyne inserts into the Cu-Mn bond of（CH₃）₃Sn-Mn（CO）₅,then the MeCuH approaches to Mn（CO）₅ to get the product,and the[Cu/Mn]catalyst is reproduced.Due to the high energy barrier of（Z）-β-production（（Z）-β-Pro）,（Z）-β-Pro can be obtained as high temperature,only（E）-β-Pro can be easily obtained at about 60℃.2.The mechanism of alkyne hydrostannylation catalyzed by[Cu/Fe]heterobimetallic catalyst is similar to that catalyzed by[Cu/Mn]catalyst.It also contains three steps:Sn-H bond activation,alkyne insertion,and vinylstannanes formation.The difference is the activation mode of Sn-H bond.In the[Cu/Fe]catalytic process,the Sn-H bond is divided into HFe（CO）₂ and Me Cu-Sn（CH₃）₃.The alkyne insertion process is the rate-determining step.Using a[Cu/Fe]heterobimetallic catalyst,bothα-Pro andβ-Pro can be easily obtained at room temperature.The different regioselectivity of alkyne hydrostannylation catalyzed by different heterobimetallic catalysts is controlled by the nucleophilicity of Cu-M pair.Thus,the product selectivity can be controlled by the Cu/M heterobimetallic pairing.3.Metal-atom-containing conjugated systems show broad application in areas of biological medicine and catalyzed chemistry.Transitional metal substituted benzothiophene is an important intermediate,due to the presence of both a lone pair and aromaticπelectrons.In this part,the aromaticity of substituted benzothiophenes,including transition metal substitution,has been studied at M06-L/aug-cc-pVDZ（aug-cc-pVDZ-pp for transition metal）level based on nuclear independent chemical shift（NICS）,πorbital and anisotropic magnetic induction current density（AICD）analysis,respectively.The influences of different substituents,as well as the different sites of thiophene ring,have been discussed.The results show that the thiophene ring is aromaticity;the aromaticity decreases after the metal substituted at C3 and the substituent adding on S site,while the effects of the kinds of metal on C3 and substituents on S site on the aromaticity are small.As hydrogen atom links to C2,the thiophene ring is aromaticity while it changes to anti-aromaticity when the bulky C₃H₇connected to C2.Our calculation results are well consistent with and provide an explanation for the experimental observations,particularly helpful for the further development of alky ne hydrostannylation and the design of other heterobimetallic catalysts.