Comparison of Isomerization Rates of the Metal Carbonyl Cluster Cp*IrCp2Co2(CO)3in Three Oxidation States (47e, 48e, 49e): Dramatic Rate Enhancements in the Odd-Electron Species

Abstract

The 48-electron cluster Cp*IrCp2Co2(CO)3 has two known isomers, one with a terminal carbonyl ligand and two edge-bridging carbonyls (1) and the other with three edge-bridging carbonyls (2). The rate of their interconversion is dramatically dependent on the number of electrons in the cluster. NMR studies establish that 2 is the thermodynamically favored isomer and that the isomerization is slow at ambient temperatures in the 48 e- complex (kisom ≈ 10-6 s-1 at 298 K). In contrast, isomerization proceeds very rapidly (kisom = 400 s-1) through the 47-electron monocation as part of an efficient electron-transfer-catalyzed process. Cyclic voltammetry and square-wave voltammetry were used to measure the isomerization rate of the monocation. The catalytic nature of the anodically-induced isomerization was diagnosed by theoretical modeling of the electrode responses and by infrared spectroelectrochemistry using a fiber-optic probe of an electrolysis solution. Reductions of the cluster isomers give 49-electron mono...