ELECTRON-TRANSFER AND ALKYL TRANSFER WITH COBALOXIMES IN AQUEOUS-SOLUTIONS - KINETIC-STUDIES BY PULSE-RADIOLYSIS

Bis(dimethylglyoximato)cobalt(III) complexes and their alkyl derivatives were reduced by solvated electrons and by various radicals in solution. Cl(py)(dmgH)(2)Co-III(lambda(max)220, 244 nm) was reduced to the Co-II state (lambda(max) 460 nm) and then to the Co-I State (lambda(max)similar to 540, similar to 630 nm). Pulse radiolysis experiments indicated that upon reduction to the Co-II state, the complex loses its Cl- and pyridine axial ligands within less than or equal to 0.5 mu s, and upon further reduction to the Co-I state, the complex takes up pyridine with a rate constant of 4.6 x 10(7) L mol(-1) s(-1). (dmgH)(2)-Co-II reacts with alkyl radicals (R) to form a Co-C bond. R(py)(dmgH)(2)Co-III (R = CH3, C6H5CH2, 4-carboxybenzyl) react rapidly with e(aq)(-) to give transient reduced species with lambda(max) near 700 nm, ascribed to R(dmgH)(2)Co-II. These species disappear by reaction with the starting material, R(py)(dmgH)(2)Co-III (k = 3.1 x 10(7) for R = CH3 and 2.2 x 10(8) L mol(-1) s(-1) for R = benzyl at pH 7), to result in the formation of dialkylcobalt complexes, whose absorption is slightly red-shifted and more intense as compared with that of the alkylcobalt complex. gamma-Radiolysis experiments also show the formation of the dialkylcobalt complex upon reduction of R(py)(dmgH)(2)Co-III with concomitant production of alkyl radicals from RX. These results are in contrast with those obtained from chemical and electrochemical experiments, where reduction of alkylcobaloxime led to dealkylation.