Exploring Acidity-Dependent PCET Pathways in Imino-Bipyridyl Cobalt Complexes

Abstract

The electrochemical proton reactivity of transition metal complexes receives intensive attention in the catalyst research. Proton-coupled electron transfer (PCET) process, influenced by coordination geometry, determines the catalytic reaction mechanisms. Additionally, the pKa of a proton source, as an external factor, plays a crucial role in regulating the proton transfer step. Understanding the effects of variations in the pKa of Brønsted acids on the PCET process is therefore essential. This study compares the PCET pathways of two high-spin cobalt (Co) complexes with contrasting exchange coupling interactions under acidic conditions with high and low pKa values. These findings reveal how proton reduction reactions in high-spin Co complexes are affected by internal factor of spin state, as well as external factor related to the proton source. The corresponding reaction mechanisms are also proposed based on these observations.