New Insights into the Mechanism of Oxidatively-Induced CO-Substitution Reaction in the Bimetallic FvCo₂(CO)₄ Gained by Digital Simulation Studies

摘要

In this study, digital simulations were performed for cyclic voltammograms (CV) obtained at differentscan rates (0.2 to 1.0 V/s) for the oxidatively-promoted CO-substitution reaction by PPh3 in thebimetallic FvCo2(CO)4,1, in CH2Cl2/0.05 M [NBu4][B(C6F5)4] in order to establish the possiblemechanism by which this reaction occurs. For the simulation input parameters, transfer coefficients ()-5 -5 2 -1 were kept at 0.5 and diffusion coefficients values of Do = 1.53 10 and 1 10 cm s were used for1 and the substitution product FvCo2(CO)3PPh3, 2, respectively. An associative mechanism that0/+ +/2+ +/0 +/2+ involves four heterogeneous electron-transfer reactions (ks) for 1 , 1 , 2 , 2 , and two+ 2+ homogeneous chemical reactions (kf) of 1 and 1 with PPh3 gave best fitting to the experimental2+ CVs. Although the inclusion of the reaction between PPh3 and 1 only slightly improves the fitting, it+ 2+ suggests that the rates and equilibrium constants for CO-substitution processes in 1 and 1 to be of1 1 1 1 the same order of magnitude. Importantly, the values of both Keq (kf /kb ) and kf were shown to be5 -1 3 -1 -1 quite large (0 M and 5 10 M s , respectively). This finding clearly demonstrates that the+ substitution of CO by PPh3 in the radical cation 1 is thermodynamically highly favored and kineticallyrapid on the voltammetric time scale.