Anodic Reaction of Co(eta(5)-C5H5)(CO)(PPh3): An Oxidatively Induced Ligand Exchange Involving a 17 e(-)/18 e(-) Redox Pair

作者：Nafady Ayman; Geiger William E^*

来源：Organometallics, 2010, 29(19): 4276-4281.

DOI：10.1021/om100631k

Unlike a number of other monocarbonyl-substituted complexes CoCp(CO)L (Cp = (eta(5)-C5H5)), chemical oxidation of the L = triphenylphosphine derivative CoCp(CO)(PPh3), 1, is known to give, in the absence of added PPh3, the disubstituted phosphine complex [CoCp(PPh3)(2)](+) rather than the simple 17-electron radical cation 1(4). Electrochemistry of 1 in CH2Cl2/[NBu4][B(C6F5)(4)] (E-1/2(1/1(+)) = -0.38 V vs ferrocene) shows that the favored anodic products depend on the concentration of 1. At low concentrations (e.g., 10(-4) M) and on the cyclic voltammetry time scale, the radical cation 1(+) dominates, but at higher concentrations and longer reaction times, a quantitative mixture of CoCp(CO)(2) and [CoCp(PPh3)(2)](+) is produced in an overall half-electron process. On the basis of cyclic voltammetry, chronoamperometry, bulk electrolysis, and IR spectroelectrochemistry, a radical-substrate mechanism is proposed involving the reaction of 1(+) with 1 to give transient [Co2Cp2(CO)(2)(PPh3)(2)](+). This putative dimer radical cation intermediate may be viewed as an odd-electron analogue of the intermediates that have previously been invoked by Kochi, Atwood, and others to explain ligand-transfer reactions between cation/anion pairs of organometallic complexes.

• 出版日期2010-10-11