The Automated Research of Concerted Proton Coupled Electron Transfer in Aquo/hydroxo/oxo Osmium Complexes

Transition metal centers play a crucial role in proton-coupled electron transfer (PCET) reactions, where subtle non-covalent interactions beyond the first coordination shell are believed to influence the mechanism and reactivity. Electrochemical techniques, such as cyclic voltammetry, have been instrumental in discerning between stepwise and concerted mechanisms of PCET processes, particularly by evaluating the pH-dependence of the apparent charge-transfer rate constant. However, the labor-intensive nature of systematic investigations across various pH conditions limits the comprehensive exploration of parameters such as proton donor/acceptor types and concentrations. Here, we propose an automated electrochemical research platform as a transformative strategy to address these limitations and enhance efficiency. We developed AutoEchem, an integrated experimentation platform that automates electrochemical testing and enables high-throughput exploration of various conditions. AutoEchem employs flow chemistry for automated liquid solution delivery in batch mode for solution preparation, titration mode for pH adjustment, and in situ electrochemical reactivation of the working electrode. The platform utilizes Python-controlled hardware and software for precise control and data analysis. We successfully validated AutoEchem by reproducing pH-dependent kinetics of [OsII(bpy)2py(OH2)]2+ from previous studies, confirming a stepwise PCET process in line with Laviron's model. Additionally, our results indicate a correlation between phosphate buffer concentration and the propensity of concerted pathways, suggesting the potential impact of buffer composition on PCET mechanisms. These findings highlight the reliability and utility of automated electrochemical research in elucidating fundamental insights into PCET processes in aqueous environments.