Eight-Electron Reduction of CO2 to CH4 by a Bioinspired Mo-Fe-S Cubane Catalyst.

Abstract

Metal-sulfur (M-S) clusters are ancient biological cofactors that catalyze CO2 and N2 reduction, yet no biological or synthetic M-S cluster has achieved sustained, high-turnover conversion of CO2 to hydrocarbons at a single active site. We reasoned that effective CO2-to-CH4 catalysis requires not only CO2 activation but also retention of a metal-bound CO intermediate for subsequent six-electron reduction. Here, a bioinspired [Cp*3Mo3S4Fe] cubane (Cp* = C5Me5) catalyzes the direct eight-electron reduction of CO2 to CH4 under ambient conditions with turnover numbers exceeding 150,000 and only trace CO formation. A structurally characterized CO2-derived anionic Fe-CO intermediate was identified, and a neutral Fe-CO cubane undergoes nearly quantitative conversion to CH4 under the catalytic conditions. These results identify synthetic M-S clusters as a competent framework for advancing catalytic CO2 reduction beyond the two-electron stage, with appropriate molecular design and reaction conditions. More broadly, they establish productive retention of a metal-bound CO intermediate as a key molecular design principle for CO2-to-hydrocarbon catalysis.

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