Aerobic oxidation of toluene and benzyl alcohol to benzaldehyde using a visible light-responsive titanium-oxide cluster

Photocatalytic selective oxidation using sunlight and O-2 can serve as a green and cost-effective method for the transformation of organic raw materials to value-added products. Here, we report a [Ti6O8(OH2)(20)](8+) cluster modified with Br- (denoted as Ti6B) triggers the selective conversion of toluene and benzyl alcohol to benzaldehyde under visible light irradiation with high efficiency. The absorption edge of Ti6B in MeCN solution is ca. 500 nm. The conversion of toluene, operated under non-solvent conditions, reached 4.7% with ca. 80% selectivity. The yield of benzaldehyde from benzyl alcohol reached 96%. Common substituents could be tolerated. ESR analyses indicate superoxide is directly involved in the reactions. The results of O-17 NMR, IR and small angle scattering indicate Ti6B is the true photocatalyst. Mechanistic studies suggest Br- binds to Ti4+ at the Ti-oxo core of Ti6B and the photo-driven electronic transition is from HOMO comprised of Br2p to LUMO + 1 comprised of Ti3d orbitals.

Automated summary

The photocalytic selective oxidation using sunlight and O-2 is a green and cost-effective method for transforming organic raw materials into value-added products. A Ti6B cluster modified with Br- was found to efficiently trigger the selective conversion of toluene and benzyl alcohol to benzaldehyde under visible light irradiation. The presence of common substituents is tolerated, and mechanistic studies suggest the involvement of superoxide in the reactions.