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

The complex [RuCl(μ-Cl)(CO)(DPCB-OMe)]<sub>2</sub> (<b>1a</b>), bearing a low-coordinated phosphorus ligand (DPCB-OMe = 1,2-bis(4-methoxyphenyl)-3,4-bis[(2,4,6-tri<i>-tert</i>-butylphenyl)phosphinidene]cyclobutene), is readily reduced to [RuH(μ-Cl)(CO)(DPCB-OMe)]<sub>2</sub> (<b>2a</b>) by the reaction with water and HSiMe<sub>2</sub>Ph. The reaction proceeds via a [RuCl<sub>2</sub>(CO)(H<sub>2</sub>O)(DPCB-OMe)] intermediate, which is characterized by X-ray diffraction analysis. Complexes <b>1a</b> and <b>2a</b> serve as highly efficient catalysts for <i>Z</i>-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)] (<b>3a</b>). It has been found that <b>3a</b> 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 <i>Z</i>-selective hydrosilylation of terminal alkynes.