REDUCTION-INDUCED CLEAVAGE OF THE COBALT CARBON BOND IN MACROCYCLIC ORGANOCOBALT COMPLEXES

The one-electron reduction of RCo(dmgBF2)2A (dmgBF2 = (difluoroboryl)dimethylglyoximato, A = pyridine or H2O, R = CH3, C2H5, C3H7, C6H5CH2, or 4-XC6H4CH2) yields RCo(dmgBF2)2A- as transients. The ESR parameters (R = 4-BrC6H4CH2, g-parallel-to = 2.23, A-parallel-to = 111 x 10(-4) cm-1, g-perpendicular-to = 2.07, A-perpendicular-to = 54 x 10(-4) cm-1) indicate that the unpaired electron resides in the d(x)2-y2 orbital of the cobalt. The reduced complexes hydrolyze in H2O to yield the alkanes RH and Co(dmgBF2)2(H2O)2. In acetonitrile the decomposition mode depends on the availability of beta-hydrogens. For R = C2H5 and 1-C3H7, the final products are the corresponding alkenes and a cobalt(II) complex of a modified macrocycle. The benzyl and substituted benzyl complexes yield the hydrolysis products 4-XC6H4CH3 and the unchanged cobalt(II) macrocycle. The kinetics of the reduction of RCo(dmgBF2)2A by R,S,-R,S-Ni(tmc)+ (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) in H2O, pH 12, are biphasic for R = benzyl and substituted benzyl and monophasic for the primary alkyl complexes, consistent with the expected effect of the organic group on the lifetimes of the RCo(dmgBF2)2A- transients.