In Situ Construction of Single-Site Ti Active Centers on Carbon Nitride for Photocatalytic Chemoselective Hydrogen Transfer Reduction

Abstract

In this work, we report an in situ construction of single-site Ti active centers on a carbon nitride surface during photocatalytic processes for one-pot chemoselective hydrogen transfer reduction of nitroaromatics and domino-type reaction using Cp2TiCl2 and −OH-enriched carbon nitride (OHCN) as precatalysts. Due to the selective adsorption of nitro and the promotion of photogenerated charge transfer by single-site Ti active species and the formation of Ti3+, the system can achieve an efficient chemoselective reduction of nitroaromatics containing various substituents, especially sensitive substituents (C═C, C≡C, C═O, C═N, C≡N, C–X (X is halogen), etc.). The two processes of chemoselective reduction of nitroaromatics and oxidation of aromatic alcohols are photocatalytically coupled to form a complete photocatalytic cycle, which allows the simultaneous formation of two high-value-added products, aromatic amines and aromatic aldehydes. More valuable products like imines are obtained by effecting the reduction of the nitro moiety to −NH2 in the presence of aromatic alcohols that can react in a domino-type process. This work guides the in situ preparation of non-noble metallic single-site photocatalysts and provides a strategy for the photocatalytic synthesis of valuable organic compounds from nitroaromatics.