title: Reactivity of electrochemically generated rhenium (II) Tricarbonyl alpha-diimine complexes: a reinvestigation of the oxidation of luminescent Re(CO)3(alpha-Diimine)Cl and related compounds.
abstract: The oxidative electrochemistry of luminescent rhenium (I) complexes of the type Re(CO) 3(LL)Cl, 1, and Re(CO) 3(LL)Br, 2, where LL is an alpha-diimine, was re-examined in acetonitrile. These compounds undergo metal-based one-electron oxidations, the products of which undergo rapid chemical reaction. Cyclic voltammetry results imply that the electrogenerated rhenium (II) species 1 ( + ) and 2 ( + ) disproportionate, yielding [Re(CO) 3(LL)(CH 3CN)] (+), 7, and additional products. Double potential step chronocoulometry experiments confirm that 1 ( + ) and 2 ( + ) react via second-order processes and, furthermore, indicate that the rate of disproportionation is influenced by the basicity and steric requirements of the alpha-diimine ligands. The simultaneous generation of rhenium (I) and (III) carbonyl products was detected upon the bulk oxidation of 1 using infrared spectroelectrochemistry. The rhenium (III) products are assigned as [Re(CO) 3(LL)Cl 2] (+), 5; an inner-sphere electron-transfer mechanism of the disproportionation is proposed on the basis of the apparent chloride transfer. Chemically irreversible two-electron reduction of 5 yields 1 and Cl (-). No direct spectroscopic evidence was obtained for the generation of rhenium (III) tricarbonyl bromide disproportionation products, [Re(CO) 3(LL)Br 2] (+), 6; this is attributed to their relatively rapid decomposition to 7 and dibromine. In addition, the 17-electron radical cations, 7 ( + ), were successfully characterized using infrared spectroelectrochemistry.
authors.affiliation: The Division of Natural Science and Mathematics, Bennington College, Bennington, Vermont 05201, USA. jbullock@bennington.edu
authors.forename: John P
authors.initials: JP
authors.lastname: Bullock
authors.forename: Eric
authors.initials: E
authors.lastname: Carter
authors.forename: Ryan
authors.initials: R
authors.lastname: Johnson
authors.forename: Abigail T
authors.initials: AT
authors.lastname: Kennedy
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Key
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Kraft
authors.forename: David
authors.initials: D
authors.lastname: Saxon
authors.forename: Patrick
authors.initials: P
authors.lastname: Underwood