Visible-Light-Driven Photocatalytic Methanol Activation on Hexagonal CdS for Triggering C─H Methylation

Light-driven methanol activation paves the way for pursuing C─H methylation of N-heteroarenes, where selectively converting methanol into the corresponding hydroxymethyl radical (•CH₂OH) is an essential prerequisite. Inspired by the versatile methanol activation on photoexcited solids, we here report a practicable semiconductor-based photocatalytic system for C─H methylation of N-heteroarenes. To be specific, hexagonal cadmium sulfide (h-CdS) was identified to be an ideal platform for visible-light-driven photocatalytic methanol activation, where selective •CH₂OH generation undergoing a hole-transfer process without any additional co-catalysts or co-solvent could trigger C─H hydroxymethylation of N-heteroarenes. The following electron transfer between photoexcited h-CdS and hydroxymethylated intermediates could finally lead to the formation of methylated N-heteroarenes. The transformations facilitate the cascade utilization of photoinduced hole and electron, thereby endowing h-CdS with extraordinary photocatalytic performance. Besides, selective generation of hydroxymethylated/methylated product could be facilely implemented in the presence/absence of electron scavengers.