Formation and homolysis of a mononuclear cobalt-oxygen adduct

Article abstract of DOI:10.1021/ja00162a030

The macrocyclic cobalt(II) complex (H₂O)_nCo(C-meso-Me₆[14]aneN₄) ²⁺ (L²Co²⁺) binds oxygen to yield L²CoO₂²⁺. The rate constants for the binding and release of O₂ in aqueous solutions at 25°C have values 5.0 × 10⁶ M^-1 s^-1 and 1.66 × 10⁴ s^-1, respectively. There is no evidence for the formation of a binuclear μ-peroxo complex. The ESR parameters of the oxygen adduct in toluene at 120 K, g_∥ = 2.108, g_⊥ = 1.96, A_∥, = 3.81 × 10^-3 cm^-1, A_⊥ = 2.94 × 10^-3 cm^-1, are consistent with the formulation of the complex as a 1:1 adduct with the unpaired spin density residing on the oxygen. The laser flash photolysis of L²CoO₂²⁺ (λ_irr 490 nm) induces the cleavage of the cobalt-oxygen bond, L²CoO₂²⁺ →^hv L²Co²⁺ + O₂.