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

Abstract

An experimental and computational chemistry study of the reactivity of [Rh(β-diketonato)(CO)(P(OCH₂)₃CCH₃)] complexes towards chemical and electrochemical oxidation shows that more electron withdrawing groups on the β-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, k₁, and a higher electrochemical oxidation potential, E_pa(Rh), linearly related by ln k₁ = −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 k₁ − 4.96(4). k₁ of [Rh(β-diketonato)(CO)(P(OCH₂)₃CCH₃)] complexes is slower than that of related [Rh(β-diketonato)(CO)(PPh₃)] and [Rh(β-diketonato)(P(OPh)₃)₂] complexes due to the better π-acceptor ability of the CO–phosphite–rhodium combination than that of CO–PPh₃–rhodium or di-phosphite–rhodium.