Dual-Synergistic S-Scheme Heterojunction for Targeting Dibenzylamine via Cascade Photoredox Catalysis of Benzylamine

Photocatalysis integrates oxidation and reduction processes, offering significant potential for driving synthetic transformations under mild conditions. However, the development of light-driven redox cascade reactions-essential for expanding reaction diversity-remains challenging and unexplored. In this study, a semiconductor cluster-based S-scheme heterojunction, T4-CdCu/ZIS, is designed for the photocatalytic redox cascade conversion of benzylamine (BA) to dibenzylamine (DBA) under a CO₂ atmosphere. The heterojunction operates via a dual internal-external synergy. Internally, Fermi level-engineered synergy enhances charge transfer kinetics, enabling rapid carrier separation and suppressed recombination while preserving favorable redox potentials. Externally, this internal synergy drives the tandem oxidation of BA to N-benzylbenzaldimine (BBAD) and its subsequent reduction to DBA, facilitated by a tight interface and highly exposed clusters. Consequently, exceptional photocatalytic BA conversion is achieved, yielding a record production rate of 8.31 mmol·g^-1·h^-1 with complete DBA selectivity. Mechanistic investigations suggest that BA undergoes dehydrocoupling on oxidative ZIS to form the BBAD intermediate, which then migrates to T4-CdCu for reduction to DBA via adsorbed H species. As proof-of-concept, a drug, Cinacalcet, exemplifies the synthesis potential of secondary amines. This work provides a sustainable route for synthesizing secondary amines and inspires the design of advanced heterojunction catalysts for efficient redox cascade reactions.