Four-electron reductive coupling of carbon monoxide: Evidence for dicarbyne and terminal carbide reaction intermediates

Abstract

The conversion of carbon dioxide (CO_2) to synthetic fuels is of significant interest in the context of renewable energy. While homo- and heterogeneous catalysts convert CO to carbon monoxide (CO) , deoxygenative coupling of CO to value- added C_(≥2) products is challenging and mechanistically poorly understood. Industrially, the Fischer- Tropsch process utilizes hydrogen to generate alkanes and alkenes from synthesis gas. The vanadium and molybdenum nitrogenases as well as oxide- derived copper electrocatalysts are capable of the reductive catenation of CO to hydrocarbons in the presence of discreet reducing equiv. and electrophiles. Little is known about the elementary reaction steps for these heterogeneous or enzymic catalytic cycles, and their reactivity is challenging to reproduce in homogeneous systems. Herein, we describe a terphenyl diphosphine molybdenum dicarbonyl that, leveraging the coordinative flexibility and redox non- innocence of the ligand scaffold, can be characterized spanning six formal oxidn. states. The metal- arene interaction allows the ligand core to act as an electron reservoir, supporting dianionic and trianion complexes. Treating these highly reduced compds. with silyl electrophiles ultimately provides a four- electron reduced C_2O_1 fragment. The ligand architecture allows for the stabilization of several reaction intermediates, including a rare terminal carbide and two distinct dicarbyne species. The characterization and reactivity of these complexes will be discussed, providing insight into design elements for challenging multi- electron transformations at a single metal site.