Reactions of (alkylperoxy)cobaloximes in acidic aqueous solutions

Bis(dimethylglyoximato)cobalt(III) complexes containing coordinated alkylperoxy groups have been studied. The compounds examined are (1) ROOCo(dmgH)2(pyridine) complexes with R = isopropyl, 2-butyl, cyclopentyl, benzyl, and isopropyl-d7 and (2) (CH3)2CHOOCo(dmgH)2L complexes with L = pyridine, piperidine, water, and ammonia. The complexes react wtih aqueous perchloric acid to form the cobalt(III) product (H2O)Co(dmgH)2L+ and a mixture of ketone and hydroperoxide. The organic products are formed in parallel pathways, each by a kinetic equation having the same algebraic form, and are the products of respective oxygen-oxygen and cobalt-oxygen bond cleavage reactions. Kinetic data were determined as a function of [H+] and, in the case of the 2-butyl complex, temperature. The rate constants for reactant disappearance and of product formation were determined, as was the ratio of ketone to hydroperoxide in the products. An important preequilibrium is the protonation of the oxime oxygens; the equilibrium constant varies in a way which reflects the basicity of the axial ligand L. The kinetic data and other results can be used to formulate a separate pathway leading to each product. Hydroperoxide formation is best accounted for by a pathway in which internal proton transfer from H+ bound to oxime oxygen occurs. Ketone production, on the other hand, shows an appreciable kinetic isotope effect: k/sup H//k/sup D/ = 8.9 +- 1.5, suggesting C-H bond breaking is a major part of the activation process