Kinetics of the reduction of a tetra-µ-acetato-dirhodium cation by substituted 1,2- and 1,4-dihydroxybenzene compounds in aqueous perchlorate media

Abstract

The kinetics of the reduction of the tetra-µ-acetato-dirhodium cation, [Rh₂(O₂CCH₃)₄(OH₂)₂]⁺([Rh₂]⁺), by substituted 1,2- and 1,4-dihydroxybenzene compounds (H₂Q) have been investigated in aqueous perchlorate media. The observed rate equation (below) is interpreted in terms of a rate-–D[Rh₂⁺]/dt= 2(k₁+k₂K₁/[H⁺])[Rh₂⁺][H₂Q] determining one-electron oxidation of H₂Q or HQ^– to a semiquinone radical intermediate. The rate constants for the cross-reactions are correlated with the semiquinone reduction potentials by means of the Marcus relationship. Self-exchange rate constants for the dihydroxybenzene/semiquinone and semiquinone/quinone couples are discussed in terms of the inner-sphere and solvent reorganization energies for electron exchange.