Cooperative α-C–H activation enabled quantitative and partial photooxidation of biomass-derived 5-hydroxymethylfurfural
Jie Li, Ye Meng, Yu Wen, Yinyin He, Putla Sudarsanam, Song Yang, Hu Li
Abstract
Photocatalytic activation of C–H bonds is versatile but challenging for undergoing oriented conversion processes. Herein, a spatially site-isolated heterojunction (ZS-Vs/ZIS) of ZnIn 2 S 4 with strong Lewis acidity (ZIS) and ZnS with S-vacancy (ZS-Vs) is constructed for activating α -C‒H bond and forming ·O 2 − to cleave the C–H bond, respectively. ZS-Vs/ZIS displays outstanding performance in visible-light partial photooxidation of bio-based 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) in an unprecedented yield of 95.7% at 25 °C. In-situ experiments and calculations reveal that Zn sites of ZIS serve as hole enrichment to adsorb HMF for α -C‒H activation via ligand-to-metal charge transfer. Shallow trap states introduced by S-vacancy in ZS-Vs act as an electron pool to realize directed O 2 activation into ·O 2 − for breaking pre-activated α -C‒H bond in HMF to exclusively give DFF. Moreover, ZS-Vs/ZIS has good recyclability and universality in the photooxidation of various alcohols to carbonyls (86.4–95.6% yields). The synergistic C–H activation/breaking strategy exhibits high potential in targeted photocatalytic transformations. A spatially site-isolated heterojunction (ZnS-Vs/ZnIn 2 S 4 ) is constructed to realize enhanced α -C-H activation for photooxidative upgrading of 5-hydroxymethylfurfural (HMF) to 2,5-furandiformaldehyde (DFF) via the synergistic effect of ligand-to-metal charge transfer (LMCT) and shallow trap states (STS). · A spatially site-isolated heterojunction with S-vacancy/Lewis acidity is constructed. · Photooxidation of HMF to DFF reaches an unprecedented yield of 95.7 % at 25 °C. · Ligand-to-metal charge transfer enables strong Lewis acidity for α-C–H activation. · Shallow trap states by S-vacancy achieve O 2 activation to .O 2 − for C–H bond breaking · The shallow trap states and built-in electric field also accelerate charge separation