Lewis acidity of cobalt(I)

Article abstract of DOI:10.1021/ic00272a011

The synthesis, characterization, and reactivity of Co^II complexes of the macrocycles (Chemical Equation Presented) are reported, where L = L¹ when R = R′ = CH₃, L = L² when R = CH₃ and R′ = Ph, and L = L⁵ when R = R′ = Ph. The complexes, denoted Co^IIL²⁺, undergo unusually facile one-electron reduction by a variety of reducing agents (e.g., Na/Hg, pyridine, N-methylimidazole) to the corresponding Co^I complexes in acetonitrile solvent. The Co¹L⁺ complexes serve as potent Lewis acids toward a variety of monodentate ligands. The equilibrium constants, K_eq, for adduct formation between CoL⁺ and the donors pyridine, 2,6-lutidine, N-methylimidazole, and Br^- have been measured by spectrophotometric methods and are reported herein. In general, K_eq increases with the donor ability of the monodentate ligand and with the electron-withdrawing ability of the macrocyclic ligand. A Lewis acid role for Co¹, which normally functions as a potent nucleophile, is highly unusual.