Rhodium complex-anchored and supramolecular polymer-grafted CdS nanoflower for enhanced photosynthesis of H2O2 and photobiocatalytic C-H bond oxyfunctionalization

Abstract

Unspecific peroxygenases exhibit high activity for the selective oxyfunctionalization of inert C(sp³)-H bonds using only H₂O₂ as a clean oxidant, while also exhibiting sensitivity to H₂O₂ concentration. CdS-based semiconductors are promising for the photosynthesis of H₂O₂ owing to their adequately negative potential for oxygen reduction reaction via a proton-coupled electron transfer process, however, they suffer from fast H₂O₂ decomposition on the surface of pristine CdS. Therefore, [Cp*Rh(bpy)H₂O]²⁺, a highly selective proton-coupled electron transfer catalyst, was anchored onto a supramolecular polymer-grafted CdS nanoflower to construct an efficient integrated photocatalyst for generating H₂O₂, mitigating the surface issue of pristine CdS, increasing light absorption, accelerating photonic carrier separation, and enhancing oxygen reduction reaction selectivity to H₂O₂. This photocatalyst promoted the light driven H₂O₂ generation rate up to 1345 µmol·L⁻¹·g⁻¹·h⁻¹, which was 2.4 times that of pristine CdS. The constructed heterojunction photocatalyst could supply H₂O₂ in situ for nonspecific peroxygenases to catalyze the C-H oxyfunctionalization of ethylbenzene, achieving a yield of 81% and an ee value of 99% under optimum conditions. A wide range of substrates were converted to the corresponding chiral alcohols using this photo-enzyme catalytic system, achieving the corresponding chiral alcohols in good yield (51%–88%) and excellent enantioselectivity (90%–99% ee).