A Ni complex of the tetradentate salen ligand HL comprising an anchoring -NH group: synthesis, characterization and electrocatalytic CO reduction to alcohols

A new salen ligand with an anchoring free amine functional group in the ligand backbone and the corresponding Ni II complex [Ni II L NH 2 ] ( 1 ) were synthesized and characterized. The complex effectively reduced CO 2 to C 1 (HCOOH, CH 3 OH) and C 2 (C 2 H 5 OH) products in a simple H-type reactor upon immobilization on the graphite electrode. Initially HCOOH was formed which was further reduced to CH 3 OH and C 2 H 5 OH in a 6e − and 12e − transfer pathway. An overall current efficiency of 49% was recorded for the formation of alcohols at −1.80 V vs. Ag/AgCl in aqueous media (ERC time 1 h, pH 7.0 and KHCO 3 0.5 M). Thus, the common limitation of the formation of deeply reduced C 2 products has been overcome. The effect of the anchoring free amine group was further established by examining the CO 2 reduction efficiency of the similar Ni II complex without having the tethered -NH 2 group. The lack of alcohol production for this case highlighted the importance of the anchoring group with the electrodes during electrochemical reduction. A new salen ligand with an anchoring free amine functional group in the ligand backbone and the corresponding Ni II complex [Ni II L NH 2 ] ( 1 ) were synthesized and characterized. Complex 1 electrocatalytically reduced CO 2 to alcohols.