Sonochemical Synthesis of Cobalt‐Oxo‐Cubanes as Redox‐Active Platform for Proton‐Coupled Electron Transfer

ABSTRACT Cobalt‐oxo‐cubanes (COCs) are efficient, earth‐abundant analogs of the tetrameric manganese clusters of the natural photosystems. Yet, the synthesis of COCs remains a challenging affair. In this study, we report a simple sonochemical approach for the gram‐scale synthesis of a series of pyridine‐substituted COCs. The representative electronic variation via para‐and meta‐substituted pyridines provided a handle to evaluate the effect of the electronic nature of COCs on the overall redox activity. Furthermore, the electrochemical behavior of COC‐XPy and its kinetics were investigated in a homogeneous system to provide insight into their solution‐phase electrochemical behavior under neutral aqueous conditions. Cyclic voltammetry (CV) studies revealed a one‐electron oxidation pathway at the [Co 4 O 4 ] 4+ core, while pH‐dependent studies revealed a proton‐coupled electron transfer (PCET) mechanism. Comparison of crude and purified samples by CV revealed that trace Co 2+ contaminants disrupt the intrinsic cubane redox chemistry and likely contributed to the oxidative currents reported in earlier studies. Overall, our approach offers a convenient route for the synthesis of COC clusters and may facilitate further studies aimed at understanding their redox behavior and relevance to artificial photosynthetic models.