Natural sunlight driven photocatalytic coupling of primary amines over TiO<inf>2</inf>/BiOBr heterojunction

Abstract

A natural sunlight active TiO2/BiOBr (TB) photocatalyst was prepared to efficiently utilize solar energy in green organic synthesis. Herein, the TB photocatalyst was evaluated for the oxidative coupling of benzylamine to N,N-dimethylbenzylamine at ambient temperature and pressure under natural sunlight for the first time. A high imine yield of ca. 89% is obtained from the TB heterojunction within 1 h, whereas only ca. 66% and 58% are observed from TiO2 and BiOBr, respectively. The TB also provides good to excellent yields when using benzylamine derivatives and N-heterocyclic amines, demonstrating the general applicability of the developed catalyst. Results from UV–Vis DRS, EIS, and photocurrent measurements reveal that such outstanding performance of the TB is mainly attributed to an extended light response range and an efficient charge separation and transfer efficiency derived from a type-II heterojunction configuration. Based on Hammett plot, radical scavenging results, and EPR spin trapping studies, the O2[rad]–-mediated imine formation mechanism under real solar light is then proposed. The present work not only provides insights into the amine coupling mechanisms which lay an important background for many C–N bond formation reactions but also highlights the possibility to apply this TB photocatalyst in near practical conditions.