Counterion Effects in Decatungstate Photocatalysis

Photocatalysis with decatungstate ([W 10 O 32 ] 4− , DT) is a versatile platform for hydrogen‐atom‐transfer (HAT)‐mediated CH functionalization under mild conditions. Decatungstate is valued for its ability to abstract hydrogen from strong aliphatic, benzylic, allylic, and α‐heteroatom CH bonds. Its efficiency is often attributed to the excited‐state reactivity of [W 10 O 32 ] 4− and substrate CH bond strength, but this view neglects the vital role of counterions, which are integral to the catalytic system and influence performance. In solution, DT forms dynamic ion‐paired ensembles where counterions affect solubility, substrate access, ion pairing, aggregation, and photostability. These factors impact activity, selectivity, productivity, and robustness. This perspective discusses counterion effects across various systems, including sodium, tetrabutylammonium, phosphonium derivatives, ionic liquids, and immobilized platforms. It highlights counterions as active components that govern catalytic parameters, aiding better catalyst design and system development.