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

The bimetallic Co(I)/Co(–I) complex [Co(CO)₂(κ³-P,N,P-PN^HP)][Co(CO)₄] shows excellent activities in the methanolysis of hydrosilanes, reaching TOF values of ca. 50 000 h⁻¹. This behavior can be ascribed to the presence of the [Co(CO)₄]^– anion, which allows for a frustrated Lewis pair mechanism, resulting in a low energy pathway for the heterolytic splitting of the Si─H bond, as substantiated by DFT calculations.

Abstract

The bimetallic Co(I)/Co(–I) complex [Co(CO)₂(κ³-P,N,P-PN^HP)][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-PN^HP)][Co(CO)₄] (2), the Co(II) complex [Co(Cl)₂(κ³-P,N,P-PN^HP)] (3), and the Co(I) complex [Co(CO)₂(κ³-P,N,P-PN^HP)]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 PN^HP 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.

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