Synthesis of Dinuclear Cobalt Silylene Complexes and Their Catalytic Activity for Alkene Hydrosilylation Reactions

A novel dinuclear silylene cobalt complex [((Me₃P)₂Co)(PMe₂)(CoCl(PMe₃))(Si(NCH₂PPh₂)₂C₆H₄)] (<b>1</b>) supported by the [PSi(silylene)P] ligand was prepared through the reaction of N-heterocyclic [PSiP] pincer ligand <b>L1</b> (HSiCl(NCH₂PPh₂)₂C₆H₄) with Co(PMe₃)₄. Complex [((Me₃P)₂Co)₂(Si(NCH₂PPh₂)₂C₆H₄)] (<b>2</b>) was formed through the reaction of complex <b>1</b> with MeLi. To the best of our knowledge, complexes <b>1</b> and <b>2</b> are the first examples of dinuclear silylene cobalt complexes supported by the [PSi(silylene)P] ligand. A new preligand <b>L2</b> (SiCl₂(NCH₂PPh₂)₂C₆H₄) was synthesized, and the reaction of preligand <b>L2</b> with Co(PMe₃)₄ afforded silyl cobalt complex [((Me₃P)₂Co)(SiCl(NCH₂PPh₂)₂C₆H₄)] (<b>3</b>). The reaction of <b>3</b> with CO delivered cobalt carbonyl complex [((Me₃P)(CO)Co)(Si(NCH₂PPh₂)₂C₆H₄)]₂O (<b>4</b>). The catalytic activity of cobalt complexes <b>1-4</b> on the hydrosilylation of alkenes was explored. Among the four complexes, complex <b>1</b> has the best catalytic activity. The catalytic process could be promoted with NaBHEt₃ as an additive, and a complete conversion with an excellent selectivity of 98:2 (b/l) could be reached at 120 °C within 8 min for aryl alkenes. A possible catalytic cycle was proposed on the basis of the experimental results and literature reports, with a cobalt hydride complex as an active intermediate. The molecular structure of complexes <b>1-4</b> was determined by single-crystal X-ray diffraction analysis.