{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, Na2 K6 H14 [(VO)6 (α-TeNb9 O33 )2 ] ⋅ 31H2 O ⋅ 2.5 C2 H8 N2 (abbreviated as V6 (TeNb9 )2 ), where a reduced {V6 } ring is sandwiched by two trivacant Keggin-type {α-TeNb9 O33 }. 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, Na5 K7 H4 [(NbO)6 (α-TeNb9 O33 )2 ] ⋅ 17H2 O (abbreviated as Nb6 (TeNb9 )2 ). Mechanism studies reveal that during the electrocatalytic oxidation process water is the only oxygen source and a key intermediate PhCH3 S+ ⋅ is involved.