Efficient Generation of Singlet Oxygen and Photooxidation of Sulfide into Sulfoxide via Tuning the Ancillary of Bicyclometalated Iridium(III) Complexes.

Abstract

With 2-phenylquinoline (pq) as a cyclometalated ligand, a series of cationic Ir(III) complexes [Ir(pq)2(L1)2](PF6) (L1 is pyridine (1a), 4-methoxypyridine (1b), 4-dimethylaminopyridine (1c), and 4-acetylpyridine (1d)) and [Ir(pq)2(L2)](PF6) (L2 is 2,2'-bipyridine (1e), 2,2'-bipyrimidyl (1f), 4,4'-dimethyl-2,2'-bipyridine (1g), and 4,4'-dimethoxy-2,2'-bipyridine (1h)) were synthesized and characterized. The influence of the metal-based highest occupied molecular orbital on triplet-state lifetime, triplet-state quantum yield, and 1O2 generation quantum yield as well as aerobic photo-oxidation of sulfide into sulfoxide was evaluated via tuning the ancillary ligand of Ir(pq)2 complexes. The results revealed that 1h with chelate ancillary ligand bearing electron-donating group possesses a high 1O2 generation quantum yield (0.90) and photocatalytic activity for sulfide oxidation with high chemoselectivity and a low catalyst loading (0.5 mol %) under mild conditions. Moreover, one-pot two-step procedure for preparation of enantiopure sulfoxides, including aerobic photo-oxidation of sulfide using 1h as a photosensitizer and chiral resolution of sulfoxide via a chiral-at-metal strategy, was also developed.