Radicals of C7-polyolefin cobalt complexes: electrochemistry, reaction routes, and structure of a resulting dimer

Abstract

The reduction and oxidation of several cyclopentadienyl (Cp) cobalt complexes with pi-bonded CTpolyolefin ligands have been studied by electrochemical methods. The cycloheptadienyl complex CpCo(n^5-C7H9)+ is reversibly reduced to a neutral radical which undergoes a slow dimerization reaction with a rate constant of k = 1.35 +- 0.23 M-1 s-1 as measured by cyclic voltammetry. X-ray crystallographic studies of the dimer confirmed that coupling took place at the C7 ligand. The dimer crystallizes in the space group P1 with a = 6.577 (1) A, b = 12.152 (2) A, c = 12.693 (2) A, beta = 100.90 (1), and Z = 2. CpCo(n4-C7H10) is reduced to a reactive monoanion that undergoes protonation and further reduction to yield CpCo(n4-C7H10). CpCo(n4-C7H10) is also reduced electrochemically, but its radical anion is very unstable and no product analysis was performed. However, CpCo(n4-C7H10) gives a cation radical upon one-electron oxidation that is stable enough to be characterized by electron spin resonance spectroscopy.