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

The preparation of the N-indolylsilylene ligand L1, N-(LSi:)-indole (L = PhC(NtBu)₂), is reported. N-Indolylsilylene cobalt(I) chloride (1) and N-indolyldiphenylphosphine cobalt(I) chloride (2) were prepared by the reaction of CoCl(PMe₃)₃ with N-indolylsilylene ligand L1 and N-indolyldiphenylphosphine L2, respectively. Both complex 1 and complex 2 were identified as highly active catalysts in alkene hydrosilylation, among which 1 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 1 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 1 is superior to any other available silylene cobalt complexes. In the process of exploring the catalytic pathway, silyl dihydrido silylene Co complex 4 was obtained from the stoichiometric reaction between complex 1 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 1, 2, and 4 were confirmed with a single-crystal X-ray diffraction technique.