Abstract
Electrochemically-promoted CO-substitution of FvCo(2)(CO)(4), 1, by using PPh3 in media composing of CH2Cl2 and the weakly coordinating [NBu4][B(C6F5)(4)] electrolyte has been achieved on both cyclic voltammetry (CV) and bulk electrolysis time scales. Using CV and in the presence of 1 equiv of PPh3, the substitution reaction is very simple, leading to the stable mono-substituted product, [FvCo(2)(CO)(3)PPh3](+)(,) 2(2+), which can be either reversibly oxidized (E-1/2 = 0.2 V) to the mono-substituted dication, [FvCo(2)(CO)(3)PPh3](2+), 2(2+), or reduced to the neutral FvCo(2)(CO)(3)PPh3, 2 at E-1/2 = -0.35 V vs Fc(0/+). Generation of these substitution products in the bulk electrolysis time scale allowed for facile measurements of their spectroscopic properties via IR and ESR spectroscopy. IR data revealed that the final product of the oxidative bulk electrolysis is the monosubstituted dication, 2(2+), with IR bands at 2114, 2091 and 2063 cm(-1). One-electron back-reduction of 2(2+) to 2(+) allowed for spectral identification of the radical monocation via IR and ESR. The fluid and frozen ESR spectra of 2(+) are in a good agreement with its IR data and consistent with having a transoid configuration. Finally, the neutral monosubstituted, 2, gave IR bands confirming the presence of one Co(CO)(PPh3) moiety at 1925cm(-1) and one Co(CO)(2) group at 2022 and 1958 cm(-1), respectively. Importantly, this work clearly demonstrates that " electrochemical switch" approach can be applied to undertake and probe COsubstitution by the stronger PPh3 nucleophile for the dinuclear FvCo(2)(CO)(4) system. This significant outcome is made possible by the greatly enhanced stability of the generated radical cations of 1 in media comprising gentle solvent and supporting electrolyte.