{V₆} Ring Sandwiched Polyoxoniobate as Molecular Electrocatalyst for Oxidant-Free Synthesis of Sulfoxides

Electrocatalytic oxidation of organic molecules to value-added chemicals has attracted recent attention. Although a series of transition metal based electrocatalytic materials have been developed, the lack of precise structure information generates great challenges in understanding the catalytic mechanism at a molecular level. Herein, we present the synthesis and characterization of a molecular electrocatalyst, Na₂K₆H₁₄[(VO)₆(α-TeNb₉O₃₃)₂] ⋅ 31H₂O ⋅ 2.5 C₂H₈N₂ (abbreviated as V₆(TeNb₉)₂), where a reduced {V₆} ring is sandwiched by two trivacant Keggin-type {α-TeNb₉O₃₃}. V₆(TeNb₉)₂ as heterogeneous electrocatalyst can selectively convert 95 % of thioanisole to sulfoxide with the Faraday efficiency up to 98 %. Notably, the important role of the embedded {V₆} ring in the electrocatalytic oxidation was illustrated by comparing with {Nb₆} ring sandwiched catalyst, Na₅K₇H₄[(NbO)₆(α-TeNb₉O₃₃)₂] ⋅ 17H₂O (abbreviated as Nb₆(TeNb₉)₂). Mechanism studies reveal that during the electrocatalytic oxidation process water is the only oxygen source and a key intermediate PhCH₃S⁺⋅ is involved.