Ligand Exchange Reaction in [Co4O4]-Cobalt Cubane: A Versatile Strategy Towards the Preparation of Cobalt Cubane-based Functional Small Molecules and Polymeric Materials

Abstract

Herein, we report the mechanistic and application study of ligand exchange reaction in Co4O4-cobalt cubane, a well-known water oxidation catalyst (WOC). The ligand exchange reaction involves the instantaneous dissociation of attached pyridine ligand and replacement of target ligand in an appropriate solvent. The kinetic and thermodynamic parameters were quantified for the ligand exchange reaction under mild conditions. Activation parameters revealed that the ligand exchange mechanism follows dissociative (D) or interchange-dissociative (Id) pathway in case of Co4O4, as it is evident by the high activation enthalpy (ΔH‡) and the positive activation entropy (ΔS‡) values. The effects of ligand derivatization, reaction temperature and type of the solvent on the exchange kinetics and the product purity were also investigated in detail. Furthermore, our theoretical studies disclosed the most probable ligand exchange pathway in case of Co4O4. Finally, this methodology was successfully applied to the preparation of Co4O4-containning functional poly-4vinylpyridine (P4VP) and cross-linked heterogeneous polymeric catalysts. The present mechanistic study clearly demonstrates that the ligand exchange method is an efficient and versatile method for the preparation of Co4O4-based functional materials.