Molecular Electrochemical Mediator for Oxidative Multi-Site Proton Coupled Electron Transfer

Proton-coupled electron transfer (PCET) allows a kinetically favorable pathway for electrochemical conversions. Inspired by this, an electrochemical mediator, N-pyridylferrocenecarboxamide (Fcpy), having site-separated electron and proton transfer sites and its analog are reported. The BDFE of the Fcpy mediator is estimated to be 80.4 kcal mol^-1. As a proof-of-concept study, Hantzsch ester (HE) having a C-H BDFE of 70.70 kcal mol^-1 has been electrochemically oxidized to yield 93% of the desired product. The computational data suggests an ET-PCET-PT process for the mediated HE oxidation with Fcpy. Further, the electrochemical HE oxidation kinetics is recorded for a series of ferrocene derivatives devoid of any Brønsted base and having different E<inf>1/2</inf> and is compared with the Fcpy and its analog. The logarithm (rate) vs E<inf>1/2</inf> for electrochemical HE oxidation shows a clear kinetic advantage for the multisite PCET mediators. Eyring analysis revealed crucial activation parameters for the MS-PCET mediator.