Driving force effects in proton coupled electron transfer

The rates of reduction of the nickel(III) oxime-imine complexes, [Ni-III(Me 2L)](+) and [Ni-III(Me2LH)](2+) by the corresponding iron(II) species are d etermined. Comparisons with rates calculated with the use of Marcus theory reveal that reactions of [Fe-II((MeLH)-L-2)](+), where the electron transfe r product is the highly acidic [Fe-III(Me2LH)](2+), show rate enhancements of several orders of magnitude. These are ascribed to a strong coupling of the electron transfer with the concomitant, thermodynamically favorable pro ton transfer. A free energy correlation supports this conclusion. (C) 2000 Elsevier Science S.A. All rights reserved.