Heterogeneous electron-transfer kinetics for some multiply bonded dirhenium complexes

Standard electrochemical rate constants k^ex_ob have been measured for the two sequential one-electron oxidations of triply-bonded dirhenium(II) complexes Re₂X₄(PR₃)₄, where X = Cl or Br, and PR₃ = a monodentate tertiary phosphine, and also for allied complexes in methylene chloride, acetonitrile, and N,N-dimethylformamide at platinum electrodes. The objective is to explore the possible dependence of k^ex_ob upon the known differences in the structural changes accompanying electron transfer. Although significant and even substantial variations in k^ex_ob were observed for closely related redox couples, the reactivity trends appear to be chiefly a consequence of differences in electrostatic work terms at the metal/solution interface. Comparisons are made with recent results for mononuclear organometallic redox couples.