Engineering boron-imidazolate-based polyoxometalates for photooxidative C=C bond cleavage in aqueous media

The direct cleavage of alkenes to access value-added carbonyls under solar-driven conditions in aqueous media presents a considerable challenge. Addressing this challenge requires the construction of effective visible-light-responsive catalysts. Herein, two boron-imidazolate-based Strandberg-type polyoxomolybdophosphate hybrids, Co(H₂O)₄[HP₂Mo₅O₂₃]₂[B(HIM)(IM)₂]₂[B(HIM)₃]₂·12H₂O (1) and Zn(H₂O)₄[HP₂Mo₅O₂₃]₂[B(HIM)(H₂IM)₂]₄·7H₂O (2) (IM = imidazole), were synthesized using a hydrothermal method and were utilized as efficient photocatalysts for the aerobic oxidative C=C bond cleavage of alkenes under natural sunlight and aqueous phase conditions. The incorporation of boron imidazolate ligands broadened the visible-light absorption region of polyoxometalates, and electrochemical tests highlighted their potential as exceptional photocatalysts. Upon visible blue light irradiation and ambient O₂ pressure in aqueous media, compound 1 exhibited remarkable aerobic photocatalytic activity, efficiently cleaving alkenes to yield the corresponding ketones (yields up to 91%). Notably, its catalytic performance remained consistent after three recycling runs under ambient sunlight, highlighting its robust stability and practical applicability. Subsequent mechanistic investigations revealed the involvement of O₂^•− species in the reaction, and a possible mechanism for the cleavage of the alkenes was proposed.