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

The bimetallic Co(I)/Co(-I) complex [Co(CO)(κ-P,N,P-PNP)][Co(CO)] (1) has shown excellent activities in the methanolysis of hydrosilanes, surpassing the related bimetallic Co(I)/Co(-I) complex [Co(CO)(PMePh)(κ-P,N,P-PNP)][Co(CO)] (2), the Co(II) complex [Co(Cl)(κ-P,N,P-PNP)] (3), and the Co(I) complex [Co(CO)(κ-P,N,P-PNP)]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)] 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 PNP ligand, followed by heterolytic splitting of the Si─H bond with the participation of the Co(I) and Co(-I) centers. Then, the PhSiH group at the Co(-I) center is transferred to the oxygen atom of a methanol molecule, which affords the [HSiPh(HOMe)] cation, regenerating the [Co(CO)] species. [HSiPh(HOMe)] protonates the hydride at the Co(I) center, leading to the formation of H and the corresponding silyl ether. Alternative reaction pathways, including alternative ionic mechanisms or NH-assisted bifunctional mechanisms, result in higher activation energies.