Heterometal Dopant Changes the Mechanism of Proton-Coupled Electron Transfer at the Polyoxovanadate-Alkoxide Surface

The transfer of two H-atom equivalents to the titanium-doped polyoxovanadate-alkoxide, [TiV₅O₆(OCH₃)₁₃], results in the formation of a V(III)-OH₂ site at the surface of the assembly. Incorporation of the group (IV) metal ion results in a weakening of the O-H bonds of [TiV₅O₅(OH₂)(OCH₃)₁₃] in comparison to its homometallic congener, [V₆O₆(OH₂)(OCH₃)₁₂], resembling more closely the thermodynamics reported for the one-electron reduced derivative, [V₆O₆(OH₂)(OCH₃)₁₂]^1-. An analysis of early time points of the reaction of [TiV₅O₆(OCH₃)₁₃] and 5,10-dihydrophenazine reveals the formation of an oxidized substrate, suggesting that proton-coupled electron transfer proceeds via initial electron transfer from substrate to cluster prior to proton transfer. These results demonstrate the profound influence of heterometal dopants on the mechanism of PCET with respect to the surface of the assembly.