HCl and O2 co-activated bis(8-quinolinolato) oxovanadium(IV) complexes as efficient photoactive species for visible light-driven oxidation of cyclohexane to KA oil

This paper reports three bis(8-quinolinolato) oxovanadium(IV) complexes that are active for visible light-induced cyclohexane oxygenation under O-2 (1 atm) in acetonitrile with HCl participation, achieving greater than 18% conversion and 86% selectivity for KA oil (cyclohexanone and cyclohexanol), along with a small amount of chlorinated product. Notably, these V(IV)OQ(2) complexes are not only basically comparable to (VO)-O-IV(acac)(2) and some typical V-V-compounds in photocatalytic activity but are also more selective for KA oil. Spectral characterizations (XPS, FT-IR and UV-vis) and DFT calculations support that V(IV)OQ(2) complexes can be co-activated by HCl and O-2 to form the (VO)-O-V(OH)-containing photoactive (PA) species with one pendant ligand's phenoxyl radical and an axially coordinated chlorine, which are responsible for the present photocatalytic oxidation. Noteworthily, increasing the Cl-substituents of V(IV)OQ(2) complexes and especially the amount of water in the reaction system obviously decelerated the generation of such PA species, which significantly improved the selectivity for KA oil.