Reduction-induced cleavage of the cobalt-carbon bond in macrocyclic organocobalt complexes

The one-electron reduction of RCo(dmgBF{sub 2}){sub 2}A (dmgBF{sub 2} = (difluoroboryl)dimethylglyoximato, A = pyridine or H{sub 2}O, R = CH{sub 3}, C{sub 2}H{sub 5}, C{sub 3}H{sub 7}, C{sub 6}H{sub 5}CH{sub 2}, or 4-XC{sub 6}H{sub 4}CH{sub 2}) yields RCo(dmgBF{sub 2}){sub 2}A{sup {minus}} as transients. The ESR parameters (R = 4-BrC{sub 6}H{sub 4}CH{sub 2}, g{sub {parallel}} = 2.23, A {sub {parallel}} = 111 {times} 10{sup {minus} 4} cm{sup {minus} 1}, g{perpendicular} = 2.07, A{perpendicular} = 54 {times} 10{sup {minus} 4} cm{sup {minus} 1}) indicate that the unpaired electron resides in the d{sub x{sup 2}{minus}y{sup 2}} orbital of the cobalt. The reduced complexes hydrolyze in H{sub 2}O to yield the alkanes RH and Co(dmgBF{sub 2}){sub 2}(H{sub 2}O){sub 2}. In acetonitrile the decomposition mode depends on the availability of {beta}-hydrogens. For R = C{sub 2}H{sub 5} and 1-C{sub 3}H{sub 7}, 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-SC{sub 6}H{sub 4}CH{sub 3} and the unchanged cobalt(II) macrocycle. The kinetics of the reduction of RCo(dmgBF{sub 2}){sub 2}A by R,S,-R,S-Ni(tmc){sup {plus}} (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) in H{sub 2}O, pH 12, are biphasic for R = benzyl and substituted benzyl andmore » monophasic for the primary alkyl complexes, consistent with the expected effect of the organic group on the lifetimes of the RCo(dmgBF{sub 2}){sub 2}A{sup {minus}} transients.« less