Iridium(III) complexes containing imidazo[1,5-a]pyridine-based ligands as photocatalysts for the [4 + 2] cycloaddition reactions of maleimides and N,N-dimethylanilines

A series of cationic iridium(III) complexes with the general formula [Ir(C^N)2(N^N)]+ (Ir1-Ir12), where C^N refers to 2-phenylpyridine and 3-phenylimidazo[1,5-a]pyridine-based cyclometalating ligands and N^N represents three imidazo[1,5-a]pyridine-based ancillary diimine ligands, were synthesized. The purpose of this work was to identify the effects of changes in the imidazo[1,5-a]pyridine backbones of the C^N and N^N ligands on the photophysical and electrochemical properties of Ir1-Ir12. The structures of the complexes were determined by NMR spectroscopy and X-ray single-crystal diffraction. Detailed studies of photophysical and electrochemical properties, supported by density functional theory (DFT) calculations, have provided a profound understanding of the electronic properties of these compounds. These complexes exhibited blue to orange-red emission, and the maximum emission wavelengths were between 436 nm and 638 nm, with excited-state lifetimes between 5.01 and 11.79 μs at 298 K. According to the DFT calculations, the emissions originated predominantly from 3LC or mixed 3MLCT/3LLCT/3LC excited states. It is found that the modifications of the C^N and N^N ligands, especially the presence of a –CF3 group in the benzene ring of the C^N ligands and the replacement of a pyridine ring by a pyrazine ring or the extension of the conjugation systems of the N^N ligands, affected the photophysical and electrochemical properties of these complexes. Compounds Ir1-Ir12 were used as photocatalysts to catalyze the [4 + 2] cycloaddition of tertiary anilines with maleimides. Complex Ir1 showed the highest catalytic activity. Under the optimized conditions, most of the reactions catalyzed by Ir1 generated cycloaddition products in satisfactory isolated yields. © 2024