Stable highly oxidizing cobalt complexes of macrocyclic ligands

Article abstract of DOI:10.1021/ja00022a033

The first crystallographically characterized neutral square-planar complex of cobalt in an oxidation state higher than 2+, Co(η⁴4-1), is reported. Structural data for this new class of compounds indicate that the macrocycle in Co(η⁴-1) is Equation Presented X = Cl, Co(η⁴-1) X = H, Co(η⁴-2) X = MeO, Co(η⁴-3) noninnocent; however, EPR data in toluene at 5.9 K (S = 1/2; g₁ = 2.558, g₂ = 2.170, g₃ = 2.017; A₂ ≈ 15 G) show that the metal center is the primary reisdence site of the unpaired electron. Co(η⁴-1) is a stable, yet potent, oxidant which is soluble in benzene and slightly soluble in pentane. The Co(η⁴-1)/[Co^III(η⁴-1)]^- couple is reversible and found at 0.550 V vs Fc⁺/Fc in CH₂Cl₂ (ca. 1.26 V vs NHE). Co(η⁴-1) slowly oxidized water, yielding H[Co^III(η⁴-1)], which may also be prepared by the reaction of [Co^III(η⁴-1)]^- with HBF₄. Both the redox and the acid/base chemistries of [Co^III(η⁴-1)]^- are reversible. Electrochemical and EPR data are also presented for Co(η⁴-2) and Co(η⁴-3).