Selective Aerobic Oxidation of Toluene to Benzaldehyde by Parallel Photoinduced Proton-Coupled Electron Transfer and...

Selectively aerobic oxidation of toluene to benzaldehyde is an important but challenging task due to the high proclivity of aldehydes to undergo over-oxidation to acids. Herein, we report a new multiphoton excitation approach for synthesizing benzaldehyde from toluene by integrating oxygen vacancy and proton-coupled electron transfer (PCET) events into one coordination polymer (Zn-AQ) to enhance efficiency and selectivity. Under light irradiation, the ligand facilitates photoinduced PCET and photoinduced energy transfer (EnT), generating radical species from the C(sp³)─H bonds and highly active ¹O₂ species. The π-stacking interactions between the ligands enforced the metal centers to form Zn⋅⋅⋅Na⋅⋅⋅Zn⋅⋅⋅Na polyoxometalate chains with oxygen vacancy sites for the selective oxidation of the radical intermediate. Zn-AQ endows the efficient and selective oxidation of aromatic benzyl C(sp³)─H bonds into aldehydes, including the conversion of toluene into benzaldehyde with the selectivity up to 94%, by combining the energies of three photons in one catalytic cycle. The first reported multiphoton catalytic strategy combines oxygen vacancy catalysis with PCET C(sp³)─H bond activation mode, providing new ideas for the design of aerobic oxidation photocatalysts for target C(sp³)─H bonds oxidation in a mild, efficient, and highly selective manner.