Iridium Complexes Containing Bis(imidazoline thione) and Bis(imidazoline selone) Ligands for Visible-Light-Induced Oxidative Coupling of Benzylamines to Imines

Novel iridium(III) complexes containing bis(N-heterocyclic carbene), bis(imidazoline thione) L2, and bis(imidazoline selone) L3 were prepared. The iridium complexes bearing L2 and L3 showed the significant absorption of visible light with maximum intensity at similar to 460 nm. Bis(2-(2'-benzothienyl)pyridinato)iridium(III) complexes (Ir-6) with L3 showed excellent ability as a photosensitizer visible light. Under blue LED irradiation with maximum emission at 460 nm, 0.25 mol % Ir-6 showed 94% conversion of benzylamine for 5 h at room temperature. Through mechanistic studies, it was suggested that the photoinduced oxidative coupling of benzylamine by Ir-6 follows a singlet oxygen pathway. The excellent performance of Ir-6 originated from the efficient visible light absorption at 460 nm and the enhanced triplet state due to the heavy-atom effect of L3. This work shows that bis(imidazoline thione) and bis(imidazoline selone) can be efficient ligands for tuning the optical properties of iridium(III) complexes.