Synthesis\nof Dinuclear Cobalt Silylene Complexes and\nTheir Catalytic Activity for Alkene Hydrosilylation Reactions

A novel dinuclear silylene cobalt complex [((Me<sub>3</sub>P)<sub>2</sub>Co)(PMe<sub>2</sub>)(CoCl(PMe<sub>3</sub>))(Si(NCH<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>C<sub>6</sub>H<sub>4</sub>)] (<b>1</b>) supported by the [PSi(silylene)P] ligand was prepared through\nthe\nreaction of N-heterocyclic [PSiP] pincer ligand <b>L1</b> (HSiCl(NCH<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>C<sub>6</sub>H<sub>4</sub>) with\nCo(PMe<sub>3</sub>)<sub>4</sub>. Complex [((Me<sub>3</sub>P)<sub>2</sub>Co)<sub>2</sub>(Si(NCH<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>C<sub>6</sub>H<sub>4</sub>)] (<b>2</b>) was formed through the reaction\nof complex <b>1</b> with MeLi. To the best of our knowledge,\ncomplexes <b>1</b> and <b>2</b> are the first examples\nof dinuclear silylene cobalt complexes supported by the [PSi(silylene)P]\n ligand. A new preligand <b>L2</b> (SiCl<sub>2</sub>(NCH<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>C<sub>6</sub>H<sub>4</sub>) was\nsynthesized, and the reaction of preligand <b>L2</b> with Co(PMe<sub>3</sub>)<sub>4</sub> afforded silyl cobalt complex [((Me<sub>3</sub>P)<sub>2</sub>Co)(SiCl(NCH<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>C<sub>6</sub>H<sub>4</sub>)] (<b>3</b>). The reaction of <b>3</b> with CO delivered cobalt carbonyl complex [((Me<sub>3</sub>P)(CO)Co)(Si(NCH<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>C<sub>6</sub>H<sub>4</sub>)]<sub>2</sub>O (<b>4</b>). The catalytic activity\nof cobalt complexes <b>1–4</b> on the hydrosilylation\nof alkenes was explored. Among the four complexes, complex <b>1</b> has the best catalytic activity. The catalytic process could be\npromoted with NaBHEt<sub>3</sub> as an additive, and a complete conversion\nwith an excellent selectivity of 98:2 (b/l) could be reached at 120\n°C within 8 min for aryl alkenes. A possible catalytic cycle\nwas proposed on the basis of the experimental results and literature\nreports, with a cobalt hydride complex as an active intermediate.\nThe molecular structure of complexes <b>1–4</b> was determined\nby single-crystal X-ray diffraction analysis.