Concerted Proton–Electron Transfer Reactivity at a Multimetallic Co<sub>4</sub>O<sub>4</sub> Cubane Cluster
Jaruwan Amtawong, Bastian Bjerkem Skjelstad, David Balcells, T. Don Tilley
Abstract
High-valent oxocobalt(IV) species have been invoked as key intermediates in oxidative catalysis, but investigations into the chemistry of proton-coupled redox reactions of such species have been limited. Herein, the reactivity of an established water oxidation catalyst, [Co4O4(OAc)4(py)4][PF6], toward H-atom abstraction reactions is described. Mechanistic analyses and density functional theory (DFT) calculations support a concerted proton–electron transfer (CPET) pathway in which the high energy intermediates formed in stepwise pathways are bypassed. Natural bond orbital (NBO) calculations point to cooperative donor–acceptor σ interactions at the transition state, whereby the H-atom of the substrate is transferred to an orbital delocalized over a Co3(μ3-O) fragment. The mechanistic insights provide design principles for the development of catalytic C–H activation processes mediated by a multimetallic oxo metal cluster.