Reactivity of Electrochemically Generated Rhenium (II) Tricarbonyl α-Diimine Complexes: A Reinvestigation of the Oxidation of Luminescent Re(CO)₃(α-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.

Covalent hybrids based on Re(i) tricarbonyl complexes and polypyridine-functionalized polyoxometalate: synthesis, characterization and electronic properties

“…To assign the oxidation potential observed for the Re complexes 4--6, we referred to the study by Bullock et al on the multiple oxidation processes of 9 in CH 3 CN. 39 This work proved that a disproportionation reaction via a bromide--bridged intermediate dimer takes place after the oxidation to form the Re II species around 1.3V. This disproportionation leads to the formation of an acetonitrile adduct, where the solvent is replacing the bromide anion.…”

Pulsed‐EPR Evidence of a Manganese(II) Hydroxycarbonyl Intermediate in the Electrocatalytic Reduction of Carbon Dioxide by a Manganese Bipyridyl Derivative

“…Indeed it has been shown that fast isomerization from fac to mer Mn II tris(carbonyl) compounds occurs after oxidation of the initial corresponding fac halide Mn I complexes. [15] Both [Mn II -(dmbpy)(CO) 3 …”

Electrochemical triggered O-atom transfer reaction in nitrocarbonyl rhenium(I) complexes: An IR spectroelectrochemical investigation

“…However, when we done the measurements (prior to the spectroelectrochemistry experiments) we have found that it was hydrated (see Section 3.1 and Fig. 1 (8) and [Re 0 (bpy)(CO) 3 (NO 2 )] À (9) were obtained in situ by spectroelectrochemistry measurements.…”

“…Many of this reaction have been shown to be chemically reversible useful to reduce electrocatalytically carbon dioxide [8,9]. Also, there is interest in the development of novel radiopharmaceuticals with specific targets.…”