Mechanistic Studies on the cis-(1+) and (3-) Oxidations of the ReIV2 Complex (4-)

Article abstract of DOI:10.1039/DT9950003317

Rate constants (25 deg C) have been determined for the oxidation of the Re(IV)2 complex di-μ-oxobis, <(C2O4)2Re(μ-O)2Re(C2O4)2>(4-), I = 1.00 M (ClO4(1-) or Cl(1-)).Whereas the complex is itself stable in air at pH 7 over many days, at lower pH there is a slow decay of the 446 nm peak (ε = 6840 M^-1cm^-1 per Re(IV)2) to give in air the colourless perrhenate(VII) (1-) product, peak at 225 nm (ε = 3400 M^-1cm^-1).The kinetics indicate a protonation step, equilibrium constant K = 2.4 M^-1, followed by the decay proces k = 4.3E-5 s^-1.With the one-equivalent oxidants cis-(1+) (1.0 V) and (3-) (0.80 V) , stoichiometries of 6 mol of oxidant per Re(IV4)2 are obtained indicating conversion through to Re(VII).Two kinetic stages have been monitored with the oxidant in large excess.For the raction with V(V) as oxidant the first stage is dependent on and as well as , giving the rate constant k1 = 3.31E4 M^-2s^-1.Since in the corresponding reaction with Mo(V) as oxidant the reaction is independent of (k_Mo = 2.27E4 M^-1s^-1), it is concluded that the V(V) reactant introduces the -dependent term.The second stage of the V(V) reaction gives the rate law dependence k_2obs = k2+k0, but with the less strong Mo oxidant k_2obs = k0 wchich is ca. 0.20 s^-1.The spectrum of the Re(IV)Re(V) intermediate, peak at 529 nm (ε = 3800 M^-1cm^-1), was obtained by stopped-flow rapid-scan spectrophotometry.Reactions of less than full stoichiometric amounts of V(V) with Re(IV)2, followed by QAE-Sephadex chromatography at 0 deg C gave orange-pink (peak at ca. 495 nm) and maroon (ca. 550 nm) intermediates, which undergo spontaneous decay.

Full text of DOI:10.1039/DT9950003317

View Article Online / Journal Homepage / Table of Contents for this issue

View Article Online

View Article Online

View Article Online

View Article Online

View Article Online