Selective photocatalytic oxidation of benzylamine to N-benzylidenebenzylamine over Pd/TiO2 single-atom catalyst with TEMPO-assisted

N-Benzylidenebenzylamine, a key imine compound, is widely used in pharmaceuticals and fine chemicals, but traditional synthesis methods suffer from harsh conditions, low selectivity, and environmental concerns. This study presents an efficient photocatalytic system using Pd/TiO 2 single-atom catalyst (Pd/TiO 2 SAC) assisted by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) for the selective oxidation of benzylamine (BZA) to N-benzylidenebenzylamine under mild conditions. The Pd/TiO 2 SAC exhibited excellent charge separation and catalytic activity due to the unique Pd-O-Ti 3+ interface, while TEMPO acted as a hydrogen atom acceptor and electron mediator, suppressing over-oxidation and enhancing selectivity. Under optimized conditions (20 mg catalyst, 0.3 mmol TEMPO, 0.4 mmol BZA, MeCN, pH 7, 4.5 h), the system achieved >99 % conversion and 98.2 % selectivity, with a turnover number (TON) of 872.89 and turnover frequency (TOF) of 193.98 h −1 . Substrate scope studies demonstrated broad applicability for substituted benzylamines, heteroaromatic amines, and aliphatic amines. Mechanistic studies, including capture experiments, EPR spectroscopy, and density functional theory (DFT) calculations, revealed that TEMPO acted as a hydrogen atom transfer (HAT) mediator, while Pd single atoms facilitated O 2 activation to generate superoxide radicals (·O 2 − ), synergistically promoting selective C N coupling. TEMPO-mediated HAT lowered the energy barrier by 39.3 %, ensuring high efficiency and selectivity. This work provides a sustainable strategy for imine synthesis via synergistic photocatalysis and radical mediation. • Pd/TiO 2 SAC and TEMPO enhanced charge separation and suppressed over-oxidation. • It achieved >99 % conversion and 98.2 % selectivity for N-benzylidenebenzylamine. • It introduced TEMPO to stabilize imine intermediates and suppress over-oxidation. • It revealed the roles of radical species and electron transfer processes. • It established an efficient method for synthesizing high-value imines.