Chemical and electrochemical oxidation of [Rh(β-diketonato)(CO)(P(OCH2)3CCH3)]: an experimental and DFT study

An experimental and computational chemistry study of the reactivity of [Rh(beta-diketonato)(CO)(P(OCH2)(3)CCH3)] complexes towards chemical and electrochemical oxidation shows that more electron withdrawing groups on the beta-diketonato ligand reduce electron density on the rhodium atom to a larger extent than electron donating groups. This leads to a slower second-order oxidative addition rate, k(1), and a higher electrochemical oxidation potential, E-pa(Rh), linearly related by ln k(1) = -11(1) E-pa(Rh) - 2.3(5). The reactivity of these complexes can be predicted by their DFT calculated HOMO energies: E-HOMO = -0.34(8)E-pa(Rh) - 5.04(4) = 0.032(5) ln k(1) - 4.96(4). k(1) of [Rh(beta-diketonato)(CO)(P(OCH2)(3)CCH3)] complexes is slower than that of related [Rh(beta-diketonato)(CO)(PPh3)] and [Rh(beta-diketonato)(P(OPh)(3))(2)] complexes due to the better pi-acceptor ability of the CO-phosphite-rhodium combination than that of CO-PPh3-rhodium or di-phosphite-rhodium.