| dc.description.abstract | The electrochemical reduction of three trinuclear complexes of general formula Cp3M3(CO)3 (Cp = n^5-cyclopentadienyl, M = Co or Rh) was studied in nonaqueous solutions. The cobalt complex Cp3CO3(CO)3 (3) is reduced by one electron to a short-lived anion (t1/2 = 2.6 s at 298 K), E0 = -1.03 V vs SCE, which decomposes to the dinuclear anion [Cp2CO2(u-C0)2]-. Two analogous Rh complexes give more persistent anions. C3v-Cp3Rh3(CO)3 (2) forms a stable monoanion, E^0 = -1.01 V, and a dianion which is stable on the cyclic voltammetry time scale, E0 = -1.75 V. The Cc trirhodium isomer Cs-CP3Rh3(CO)3 (1) is reduced in a first step to an anion somewhat less stable than that of 2, Eo = -1.22 V, and in a second step to an unstable dianion, Ep = -1.73 V. The more positive E^0 for 2^0/- compared to1^0/- is consistent with the higher electron-withdrawing ability of bridging as opposed to terminal CO groups. The enhanced kinetic stability of the cluster core when M = Rh rather than Co probably arises from the greater M-M bond strength of the second row metal. When the rest potential for voltammetric scans of 1 is more positive than about +0.2 V, the peaks are those of 2 rather than 1. This is shown to be due to anodic electrocatalysis of the Cs to C3v isomerization. The minimum enhancement of the isomerization rate of the 47e- Cs monocation over that of the 48e- neutral complex is about 10^5. | en_US |
