Low-Coordinate Cobalt Fluoride Complexes: Synthesis, Reactions, and Production from C–F Activation Reactions

A cobalt(II) fluoride complex, [L t Bu Co(μ-F)] 2 [L t Bu = 2,2,6,6-tetramethyl-3,5-bis(2,6-diisopropylphenylimido)hept-4-yl], was synthesized from L t Bu Co using Me 3 SnF via homolytic cleavage of the Sn–F bond. L t Bu Co also performed the overall binuclear oxidative addition of fluorinated arenes to give [L t Bu Co(μ-F)] 2 and a cobalt(II) aryl complex of the corresponding fluorobenzene substrate in a 1:2 molar ratio. The C–F activation reaction has a first-order rate dependence on both cobalt and fluorobenzene concentrations. The rate is increased by meta -fluoride substituents, and slowed by ortho -fluoride substituents, suggesting electronic and steric influences on the transition state, respectively. The data are most consistent with a mechanism beginning with rate-limiting oxidative addition of the aryl fluoride to cobalt(I), followed by rapid reduction of the cobalt(III) aryl fluoride intermediate by a second molecule of L t Bu Co. [L t Bu Co(μ-F)] 2 also reacts with Et 3 SiH to give the hydride complex [L t Bu Co(μ-H)] 2 . This hydride complex has low reactivity toward alkenes and N 2, in contrast to an earlier report.