title: Photochemical Processes in a Rhenium(I) Tricarbonyl N-Heterocyclic Carbene Complex Studied by Time-Resolved Measurements.
abstract: 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.
authors.affiliation: Department of Chemistry, School of Science, Tokyo Institute of Technology , O-okayama, Meguro-ku, Tokyo 152-8551, Japan.
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Mukuta
authors.affiliation: Department of Chemistry and Nanochemistry Research Institute, Curtin University , Kent Street, Bentley, 6102 Western Australia, Australia.
authors.forename: Peter V
authors.initials: PV
authors.lastname: Simpson
authors.affiliation: Department of Chemistry and Nanochemistry Research Institute, Curtin University , Kent Street, Bentley, 6102 Western Australia, Australia.
authors.forename: Jamila G
authors.initials: JG
authors.lastname: Vaughan
authors.affiliation: Centre for Microscopy, Characterisation and Analysis, University of Western Australia , Crawley, 6009 Western Australia, Australia.
authors.forename: Brian W
authors.initials: BW
authors.lastname: Skelton
authors.affiliation: Department of Industrial Chemistry "Toso Montanari," University of Bologna , viale del Risorgimento 4, I-40136 Bologna, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Stagni
authors.affiliation: Department of Chemistry and Nanochemistry Research Institute, Curtin University , Kent Street, Bentley, 6102 Western Australia, Australia.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Massi
authors.affiliation: National Institute of Advanced Industrial Science and Technology , 16-1 Onogawa, Tsukuba 305-8569, Japan.
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Koike
authors.affiliation: Department of Chemistry, School of Science, Tokyo Institute of Technology , O-okayama, Meguro-ku, Tokyo 152-8551, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Ishitani
authors.affiliation: Interactive Research Center of Science, Tokyo Institute of Technology , Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8502, Japan.|PRESTO, Japan Science and Technology Agency (JST) , 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Ken
authors.identifier: http://orcid.org/0000-0003-1724-2009
authors.initials: K
authors.lastname: Onda