Photochemical Processes in a Rhenium(I) Tricarbonyl N-Heterocyclic Carbene Complex Studied by Time-Resolved Measurements

open9siThe authors thank Professor S. Koshihara and Dr. S. Tanaka at Tokyo Institute of Technology for various discussions. This study was supported by the JST-PRESTO, JST-CREST, and JSPS-AnApple (All Nippon Artificial Photosynthesis Project for Living Earth). T.M. was supported by JSPS Research Fellowship for Young Scientists. Access to the facilities at the Centre for Microscopy, Characterisation and Analysis, University of Western Australia, is also kindly acknowledged. M.M. wishes to thank the Australian Research Council for the Future Fellowship (FT130100033).We carried out time-resolved infrared (TR-IR) and emission lifetime measurements on a Re(I) carbonyl complex having an N-heterocyclic carbene ligand, namely, fac-[Re(CO)3(PyImPh)Br], under photochemically reactive (in solution in acetonitrile) and nonreactive (in solution in dichloromethane) conditions to investigate the mechanism of photochemical ligand substitution reactions. The TR-IR measurements revealed that no reaction occurs on a picosecond time scale and the cationic product, namely, fac-[Re(CO)3(PyImPh)(MeCN)]+, is produced on a nanosecond time scale only in solution in acetonitrile, which indicates that the reaction proceeds thermally from the excited state. Because no other products were observed by TR-IR, we concluded that this cationic product is an intermediate species for further reactions. The measurements of the temperature-dependent emission lifetime and analysis using transition-state theory revealed that the photochemical substitution reaction proceeds from a metal-to-ligand charge transfer excited state, the structure of which allows the potential coordination of a solvent molecule. Thus, the coordinating capacity of the solvent determines whether the reaction proceeds or not. This mechanism is different from those of photochemical reactions of other types of Re(I) carbonyl complexes owing to the unique characteristics of the carbene ligand.openMukuta, Tatsuhiko; Simpson, Peter V.; Vaughan, Jamila G.; Skelton, Brian W.; Stagni, Stefano; Massi, Massimiliano; Koike, Kazuhide; Ishitani, Osamu; Onda, KenMukuta, Tatsuhiko; Simpson, Peter V.; Vaughan, Jamila G.; Skelton, Brian W.; Stagni, Stefano; Massi, Massimiliano; Koike, Kazuhide; Ishitani, Osamu; Onda, Ke