Effect of Lewis Basic Amine Site on Proton Reduction Activity of NNN-Co Pincer Complex

Abstract

Electrochemical proton reduction is a promising energy storage method because H-2 molecule has a simple structure with a relatively low potential energy. Current interest in hydrogen catalysts has increased research efforts on synthetic analogs of hydrogenase active sites. In this study, we demonstrated the electrochemical H-2 evolution reactivity of [NNN(R)-Co(CH3CN)(3)](2+) (R (sic) CH2 (1b), NCH3 (2b)) complexes and examined a proton-relay process in the H-2 evolution reaction (HER). Upon one-electron reduction, the Co(II) ion center in a high-spin state dissociated a CH3CN ligand, while opening a reaction site. Cyclic voltammograms of the Co complexes indicated quasi-reversible Co(II/I) redox behaviors, and both complexes 1b and 2b showed catalytic H-2 evolution activity. Interestingly, 2b, assisted by a proton-relaying NCH3 group, exhibited more efficient catalytic activity than 1b.