A Homobimetallic Frustrated Lewis Pair Cobalt Catalyst for the Methanolysis of Hydrosilanes.

Abstract

The bimetallic Co(I)/Co(-I) complex [Co(CO)2(κ3-P,N,P-PNHP)][Co(CO)4] (1) has shown excellent activities in the methanolysis of hydrosilanes, surpassing the related bimetallic Co(I)/Co(-I) complex [Co(CO)(PMe2Ph)(κ3-P,N,P-PNHP)][Co(CO)4] (2), the Co(II) complex [Co(Cl)2(κ3-P,N,P-PNHP)] (3), and the Co(I) complex [Co(CO)2(κ3-P,N,P-PNHP)]Cl (4). A comprehensive DFT study of the plausible reaction mechanisms indicates that the enhanced activity of 1 can be attributed to the presence of the [Co(CO)4]- anion, which enables a frustrated Lewis pair (FLP) mechanism that provides a low energy pathway for the heterolytic splitting of the Si-H bond. The reaction mechanism entails the coordination of the hydrosilane to the Co(I) center upon decoordination of the amine functionality of the PNHP ligand, followed by heterolytic splitting of the Si-H bond with the participation of the Co(I) and Co(-I) centers. Then, the PhSiH2 group at the Co(-I) center is transferred to the oxygen atom of a methanol molecule, which affords the [H2SiPh(HOMe)]+ cation, regenerating the [Co(CO)4]- species. [H2SiPh(HOMe)]+ protonates the hydride at the Co(I) center, leading to the formation of H2 and the corresponding silyl ether. Alternative reaction pathways, including alternative ionic mechanisms or NH-assisted bifunctional mechanisms, result in higher activation energies.