The electrochemical behaviour of the series of ten [Rh(RCOCHCOR')(P(OPh)(3))(2)] complexes with R, R' = CF3, CF3 (1), CF3, CH3 (2), CF3, Ph (C6H5) (3), CF3, Fc (ferrocenyl = (C5H5)Fe(C5H4)) (4), CH3, Ph (5), CH3, CH3 (6), Ph, Ph (7), Fc, CH3 (8), Fc, Ph (9) and Fc, Fc (10) were studied in acetonitrile containing 0.100 mol dm(-3) tetra-n-butylammonium hexafluorophosphate as supporting electrolyte utilizing a glassy carbon working electrode. Results are consistent with Rh(I) being first oxidized in an electrochemically irreversible two-electron transfer process at peak anodic potentials ranging E-pa(Rh)= 0.124-0.881V vs. Fc/Fc(+). For the ferrocene-containing complexes (4), and (8)-(10) the rhodium oxidation was followed by the electrochemically reversible oxidation of the ferrocenyl group in a one-electron transfer process at a slightly more positive potential. Relationships were established between the electrochemical quantity E-pa(Rh) and kinetic parameter log k(2) as well the sum of experimental group electronegativities (Gordy Scale) of the R and R' groups (chi(R) + chi(R')), the Hammett sigma values (sigma(R) + sigma(R')) and the Lever ligand parameter E-L for the [Rh(RCOCHCOR')(P(OPh)(3))(2)] complexes: E-pa(Rh) (vs. Fc/Fc(+)/V) = 0.31 (chi(R) + chi(R'))-1.09=0.56 (sigma(R) + sigma(R'))+ 0.28 =S-M (Sigma E-L) + (I-M - 0.66 V) = -0.23 log k(2) - 0.03 (k(2) = second order rate constant for the oxidative addition of methyl iodide to rhodium). A profound shift of E-pa(Rh) to a more positive potential was observed for Rh(I) substrates containing beta-diketonato ligands with increasing electronegative substituents R and R'. An exponential dependence of E-pa(Rh) on the p(Ka), of the beta-diketone was obtained. (C) 2011 Elsevier Ltd. All rights reserved.