title: Mechanism of the photochemical ligand substitution reactions of fac-[Re(bpy)(CO)(3)(PR(3))](+) complexes and the properties of their triplet ligand-field excited states.
abstract: We report herein the mechanism of the photochemical ligand substitution reactions of a series of fac-[Re(X(2)bpy)(CO)(3)(PR(3))](+) complexes (1) and the properties of their triplet ligand-field ((3)LF) excited states. The reason for the photostability of the rhenium complexes [Re(X(2)bpy)(CO)(3)(py)](+) (3) and [Re(X(2)bpy)(CO)(3)Cl] (4) was also investigated. Irradiation of an acetonitrile solution of 1 selectively gave the biscarbonyl complexes cis,trans-[Re(X(2)bpy)(CO)(2)(PR(3))(CH(3)CN)](+) (2). Isotope experiments clearly showed that the CO ligand trans to the PR(3) ligand was selectively substituted. The photochemical reactions proceeded via a dissociative mechanism from the (3)LF excited state. The thermodynamical data for the (3)LF excited states of complexes 1 and the corrective nonradiative decay rate constants for the triplet metal-to-ligand charge-transfer ((3)MLCT) states were obtained from temperature-dependence data for the emission lifetimes and for the quantum yields of the photochemical reactions and the emission. Comparison of 1 with [Re(X(2)bpy)(CO)(3)(py)](+) (3) and [Re(X(2)bpy)(CO)(3)Cl] (4) indicated that the (3)LF states of some 3- and 4-type complexes are probably accessible from the (3)MLCT state even at ambient temperature, but these complexes were stable to irradiation at 365 nm. The photostability of 3 and 4, in contrast to 1, can be explained by differences in the trans effects of the PR(3), py, and Cl(-) ligands.
authors.affiliation: National Institute of Advanced Industrial Science and Technology, Onogawa 16-1, Tsukuba 305-8569, Japan. k-koike@aist.go.jp
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Koike
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Okoshi
authors.forename: Hisao
authors.initials: H
authors.lastname: Hori
authors.forename: Koji
authors.initials: K
authors.lastname: Takeuchi
authors.forename: Osamu
authors.initials: O
authors.lastname: Ishitani
authors.forename: Hideaki
authors.initials: H
authors.lastname: Tsubaki
authors.forename: Ian P
authors.initials: IP
authors.lastname: Clark
authors.forename: Michael W
authors.initials: MW
authors.lastname: George
authors.forename: Frank P A
authors.initials: FP
authors.lastname: Johnson
authors.forename: James J
authors.initials: JJ
authors.lastname: Turner