Synthesis, properties and photocatalytic activities of iridium(Ⅲ) complexes based on the derivatives of imidazo[1,5-a]pyridine with electron-withdrawing groups

Abstract

Twelve cationic cyclometalated iridium(III) complexes with the general formula [Ir(C^N)₂(N^N)]PF₆ (Ir1-Ir12), where C^N are cyclometalated ligands, including 2-(2,4-difluorophenyl)pyridine (dfppy), 2-(4-(trifluoromethyl)phenyl) pyridine (CF₃ppy), and 1-(4-(trifluoromethyl)phenyl)isoquinoline (CF₃piq) and where N^N represents 3-(pyridin-2-yl)imidazo[1,5-a]pyridine-based ancillary ligands, were successfully synthesized and structurally characterized via NMR and X-ray diffraction. The targets of this work were to investigate the effects of changes in the C^N and N^N ligands of the iridium(III) complexes on their photophysical, electrochemical, and catalytic properties. DFT and TD-DFT calculations were also utilized to support the photophysical and electrochemical property studies. The intense green to orange-red emissions of Ir1-Ir12 arose from the ³ILCT/³LLCT/³MLCT transition in the spectral range between 498 and 603 nm, with excited-state lifetimes between 4.61 and 7.45 μs. These complexes were used as photocatalysts for the [4 + 2] cycloaddition of maleimides and N,N-dimethylanilines. Complex Ir7 showed excellent catalytic activity, affording products in moderate to high yields (42 %-92 %) from a wide range of substrates under mild conditions.