Synthesis of ethane from CO₂ by a methyl transferase-inspired molecular catalyst.

Abstract

Molecular catalysts with a single metal center are reported to reduce CO₂ to a wide range of valuable single-carbon products like CO, HCOOH, CH₃OH, etc. However, these catalysts cannot reduce CO₂ to two carbon products like ethane or ethylene and the ability to form C-C from CO₂ remains mostly limited to heterogeneous material-based catalysts. We report a set of simple iron porphyrins with pendant thiol group can catalyze the reduction of CO₂ to ethane (C₂H₆) with H₂O as the proton source with a Faradaic yield >40% the rest being CO. The mechanism involves a CO₂-derived methyl group transfer to the pendant thiol akin to the proposal forwarded for methyl transferases and a follow-up C-C bond formation of the thioether thus formed and a Fe(II)-CH₃ species generated by the reduction of a second molecule of CO₂. The availability of a "parking space" in the molecular framework for the first reduced C₁ product from CO₂ reduction allows C-C bond formation resulting in a unique case where a component of natural gas can be generated from direct electrochemical reduction of CO₂.