Multisite Proton–Coupled Electron Transfer at a Keggin-Type Polyoxotungstate

High Resolution Image Download MS PowerPoint Slide 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 Δ H ‡ 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.