Synthesis and Reactions of Diphosphinidenecyclobutene Ruthenium Complexes Relevant to Catalytic Hydrosilylation of Terminal Alkynes

The complex [RuCl(μ-Cl)(CO)(DPCB-OMe)] 2 ( 1a ), bearing a low-coordinated phosphorus ligand (DPCB-OMe = 1,2-bis(4-methoxyphenyl)-3,4-bis[(2,4,6-tri -tert -butylphenyl)phosphinidene]cyclobutene), is readily reduced to [RuH(μ-Cl)(CO)(DPCB-OMe)] 2 ( 2a ) by the reaction with water and HSiMe 2 Ph. The reaction proceeds via a [RuCl 2 (CO)(H 2 O)(DPCB-OMe)] intermediate, which is characterized by X-ray diffraction analysis. Complexes 1a and 2a serve as highly efficient catalysts for Z -selective hydrosilylation of phenylacetylene. The reason for the high catalyst efficiency of DPCB-OMe complexes has been investigated by reaction and structure analysis of the presumed intermediate [Ru(CH═CHPh)Cl(CO)(DPCB-OMe)] ( 3a ). It has been found that 3a has ample space to associate with hydrosilane and, therefore, readily undergoes metathesis between Ru−C and H−Si bonds. This structural feature in conjunction with the strong π-accepting ability of the DPCB-OMe ligand leads to highly efficient catalysis for Z -selective hydrosilylation of terminal alkynes.