Heterogeneous visible-light photoredox catalysis with NiCl2@g-C3N4 for induced C(sp2)-H/N H cross-dehydrogenative coupling

• The use of semiconductor materials to catalyze the activation of C(sp 2 )-H bonds avoids the disadvantages of using conventional methods and transition metal catalysis , and the NiCl 2 @g-C 3 N 4 as a photocatalyst can stimulate N H bond fracture and promote C(sp 2 )-H activation. • The introduction of Ni 2+ as electron acceptor in the new catalyst NiCl 2 @g-C 3 N 4 improves the separation and transfer efficiency of the carrier, which is much higher than the photoreaction efficiency of g-C 3 N 4 . • The NiCl 2 @g-C 3 N 4 generates photogenerated electrons and electron holes upon visible light irradiation , which act as scar-free oxidants producing radicals, and does not require external chemical oxidants. • The catalyst could be recycled and reused for 6 times without obvious loss of catalytic activity. A novel photoactive NiCl 2 @g-C 3 N 4 catalyst system, which effectively drives C(sp 2 )-H/N H bond formation between quinolin-2(1 H )-ones, primary and secondary aliphatic amines under blue light irradiation. The NiCl 2 @g-C 3 N 4 composite with a NiCl 2 loading of 0.7wt% had the highest photoactivity, and the calculated band gap energy value is 2.56 eV The nickel ion could act as an electron acceptor enhancing carrier separation and transfer efficiency, greatly enhanced the photoreaction efficiency of g-C 3 N 4 . Preliminary mechanistic studies indicate upon visible light irradiation, the photo-generated electrons and holes act as oxidants, thereby generating amine radicals in the absence of external chemical oxidants. This provides a straightforward and efficient approach for directly 3-aminating quinoxalines-2(1 H )-ones. Moreover, the heterogeneous catalyst can be recycled at least six times without significant activity loss.