The Study Of Cobalt Complexes Of Geometry-Constrained Iminopyridyl Ligands In The Application Of Alkyne Hydrosilylation

Hydrosilylation of C-C unsaturated bonds has become an important synthetic method for organosilanes of fine organic chemicals and intermediates.Thermal reaction,photocatalysis,and transition metal catalysis are the most common ways in hydrosilylation.Among them,hydrosilylation of C-C unsaturated bond via transition metal catalysis features mild conditions and high selectivity,and different isomers of silanes can be obtained by adjusting the structure of catalyst.Therefore,it has attracted a widespread attention in both academia and industry,and becomes one of the hot topics in current synthetic chemistry and homogeneous catalysis.In the preparation of vinylsilanes via hydrosilylation of alkynes,efficiently control of the regio-and stereoselectivity has always been the major challenge.Recently,the hydrosilylation of terminal alkynes with secondary silane has been well studied,while fewer hydrosilylations of alkynes with primary silanes are explored,which is still a challenge in current research.Therefore,development new ligands and their transition metal complex catalysts for hydrosilylation of alkynes is of great significance.This paper briefly describes the 3d metal-catalyzed hydrosilylation and the mechanism of cobalt-catalyzed hydrosilylation of alkyne,which focuses on the following two aspects of research:1.With cobalt complexes as the catalyst,which were in-situ prepared with our developed bidentated geometry-constrained iminopyridyl?CIm Py?compounds,the hydrosilylation of terminal alkyne with phenylsilane was explored.The results showed that in THF with the cobalt complex as the catalyst,which was in-situ prepared from Co?OAc?₂ and L5,phenylsilane and phenylacetylene reacted to produce the hydrosilylation product in high Markov selectivity and excellent isolated yield,thus the reaction model was established.With the optimal conditions,we subsequently examined the scope of this hydrosilylation.The results suggested that the catalytic system is well compatible with aryl alkynes with electron-withdrawing and electron-donating groups,heteroaryl alkynes,internal alkynes and enynes as well.Scale-up reaction goes smoothly.Moreover,diphenylsilane could also be tolerated in this catalytic system after a small modification,but the yield is moderate.2.Using the reaction of phenylacetylene with phenylsilane as the model,the kinetic investigation of Co?OAc?₂/L5 catalytic system was performed by in-situ IR.The results showed that the reaction behaves a negative first-order kinetic behavior with the concentration of phenylacetylene,and first-order kinetic behaviors with the concentration of phenylsilane,catalyst and ligand.We proposed that the silylcobalt species was produced when cobalt acetate,ligand and phenylsilane was mixed.Then the silylcobalt species was coordinated with alkyne followed by regioselective and stereo-selective 1,2-syn-insertion to form syn-alkenylcobalt complex,which reacted with Ph Si H₃ to releases?-alkenylsilane.The rate-limiting step might be the reaction between syn-alkenylcobalt complex and Ph Si H₃.The ligand played a crucial role in the catalytic cycle,which contributes to a high TON up to 20000.