Abstract
The anodic oxidation of Co(2)Fv(CO)(4), 1, has been studied in dichloromethane containing [NBu4][TFAB] (TFAB = [B(C6F5)(4)](-)) as the supporting electrolyte anion. Voltammetric, amperometric, coulometric, and in situ spectroelectrochemical methods showed that 1 is oxidized in two one-electron steps to 1(+) (E-1/2 = 0.06 V) and 1(2+) (E-1/2 = 0.51 V) in fast, diffusion-controlled processes without evidence of product adsorption at glassy carbon electrodes. Whereas the neutral compound has a transoid configuration of the two metals, IR and ESR spectra of the monocation 1(+) are best interpreted as arising from a cisoid structure with a Co-Co bond. Analysis of the ESR data suggests that the SOMO of 1+ is significantly delocalized over the metal and ligand moieties. The discrete one-electron reactions of the 1/1(+)/12(+) electron-transfer series stand in contrast to the direct two-electron processes observed for analogous group 6 and group 8 dileptic fulvalenediyl complexes. The radical cation 1+ undergoes rapid substitution of a CO group when it is electrochemically generated in the presence of added PPh3. Cyclic voltammetry simulations establish a substitution rate constant of 5 x 10(3) M-1 s(-1) for the reaction. Bulk oxidation of 1 in the presence of 1 equiv of PPh3 yields only the monosubstituted dication [Co(2)Fv(CO)(3)(PPh3)](2+), 2(2+), as shown by IR spectroscopy. One-electron back-reduction of 2(2+) to 2(+) allowed spectral identification of the radical cation of the substitution product. Study of the anodic products of Co(2)Fv(CO)(4) was made possible by substitution of a traditional supporting electrolyte anion ([PF6](-) or [BF4](-)) by the weakly coordinating TFAB anion.