N-Indolylsilylene Cobalt(I) Chloride: A Base Metal Catalyst for Alkene Hydrosilylation

The preparation of the N-indolylsilylene ligand <b>L1</b>, N-(LSi:)-indole (L = PhC(NtBu)₂), is reported. N-Indolylsilylene cobalt(I) chloride (<b>1</b>) and N-indolyldiphenylphosphine cobalt(I) chloride (<b>2</b>) were prepared by the reaction of CoCl(PMe₃)₃ with N-indolylsilylene ligand <b>L1</b> and N-indolyldiphenylphosphine <b>L2</b>, respectively. Both complex <b>1</b> and complex <b>2</b> were identified as highly active catalysts in alkene hydrosilylation, among which <b>1</b> showed superior performance compared to that of CoCl(PMe₃)₃ and any other available silylene cobalt complexes. The experimental results indicate that when aryl alkenes are used as substrates, complex <b>1</b> can efficiently and selectively produce Markovnikov addition products at 50 °C within 10 min. The catalytic system is very fast, and the catalytic activity of complex <b>1</b> is superior to any other available silylene cobalt complexes. In the process of exploring the catalytic pathway, silyl dihydrido silylene Co complex <b>4</b> was obtained from the stoichiometric reaction between complex <b>1</b> with Ph₂SiH₂. N-Indolylsilylene cobalt(I) hydride is considered an active catalyst for this system in the proposed catalytic mechanism. The molecular structures of the cobalt complexes <b>1</b>, <b>2</b>, and <b>4</b> were confirmed with a single-crystal X-ray diffraction technique.