Electrocatalytic CO₂ Reduction with a Half‐Sandwich Cobalt Catalyst: Selectivity towards CO

Abstract

We present herein a Cp*Co(III)‐half‐sandwich catalyst system for electrocatalytic CO2 reduction in aqueous acetonitrile solution. In addition to an electron‐donating Cp* ligand (Cp*=pentamethylcyclopentadienyl), the catalyst featured a proton‐responsive pyridyl‐benzimidazole‐based N,N‐bidentate ligand. Owing to the presence of a relatively electron‐rich Co center, the reduced Co(I)‐state was made prone to activate the electrophilic carbon center of CO2. At the same time, the proton‐responsive benzimidazole scaffold was susceptible to facilitate proton‐transfer during the subsequent reduction of CO2. The above factors rendered the present catalyst active toward producing CO as the major product over the other potential 2e/2H+ reduced product HCOOH, in contrast to the only known similar half‐sandwich CpCo(III)‐based CO2‐reduction catalysts which produced HCOOH selectively. The system exhibited a Faradaic efficiency (FE) of about 70% while the overpotential for CO production was found to be 0.78 V, as determined by controlled‐potential electrolysis.

New Borrowing Hydrogen Mechanism for Redox-Active Metals

“…The high-valent organometallic cobalt system Cp*Co III is an active catalyst for the hydrogenation of CO2 [21][22][23] and carbonates, 24 as well as for the dehydrogenation of ammonia borane 25 and secondary alcohols. 26 It was also shown to promote a family of organic transformations that involve borrowing hydrogen chemistry.…”