Electrochemical and reactivity comparisons among isoelectronic oxo, imido,and nitrido complexes of rhenium and osmium

Cyclic voltammetry has been used to study the electrochemical properties of 29 isoelectronic and isostructural osmium(VI)-nitrido, rhenium(lr)-oxo, an d rhenium(V)-imido complexes of the form Tp(()*M-)(E)(X)(Y) [Tp(()*()) = Tp , HB(pz)(3); or Tp*, HB(3,5-Me(2)pz)(3)]. Oxidations from d(2) to d(1) spec ies are typically reversible or quasi-reversible, while reductions to d(3) species are usually irreversible. The E-1/2 values for oxidation vary from > + 2 V for TpOs(N)(Cl)(2) to - 0.11 V for TpRe(Ntolyl)(Ph)(Me) (vs. Cp2Fe , 0 in MeCN/(Bu4NPF6)-Bu-n). The potentials follow simple trends, Os(N) > Re(O) > Re(Ntolyl) and Tp > Tp*. Potentials for TpM(E)(X)(Y) are also affec ted by the X and Y ligands, with OTf > Cl congruent to I > Ph > alkyl, corr elating with the Hammett a values for X and Y. In contrast, peak potentials for reduction of the compounds (ca. - 1.0 to - 1.5 V) do not follow simple patterns. The reactivity of these complexes as inner-sphere oxidants does not correlate with their peak reduction potentials. Rather. the ease of oxi dation of the compounds better parallels their reactivity as oxidants. (C) 1999 Elsevier Science S.A. All rights reserved.