Abstract
Proton-coupled electron transfer (PCET) governs many redox transformations, but is thermodynamically constrained when proton and electron transfer occur at a single site. Here, we introduce a new multisite PCET (MS-PCET) platform, based on the Keggin-type polyoxotungstate, [VW(12)O(40)](3-) (VW(12)). Pairing VW(12) with either Brønsted bases or acids yields reagent pairs with tunable effective bond dissociation free energies (BDFE(eff)) over 15 kcal mol(-1), enabling both oxidative and reductive H atom transfer reactions. Kinetic studies on the oxidative pathway by using 2,4,6-(t)Bu(3)PhOH as a model hydrogen atom (H atom) donor reveal a product-like, entropy-dominated concerted proton-electron transfer (CPET) pathway from a preorganized hydrogen-bonded complex. By contrast, reductive H atom transfer reactions exhibit larger ΔH(‡) values, measurable kinetic isotope effects, and balanced Brønsted slope, consistent with synchronous CPET-type mechanism. Extension to N-H, O-H, and C-H substrates demonstrates the versatility of the VW(12) MS-PCET platform for tunable (de)hydrogenation.