H3O2−, O22− and O2˙− bridging ligands in cobalt(iii) complexes of an acyclic phenolate-hinged dinucleating ligand

Abstract

The dicobalt(III) complex, [Co₂(bpbp)(μ-H₃O₂)₂](ClO₄)₃ (bpbp⁻ = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-tert-butylphenolate), obtained by reaction of cobalt(II) perchlorate with Hbpbp under ambient conditions contains two μ-H₃O₂⁻ bridging ligands. The H-bonded O⋯O distances in this motif are 2.437(3) and 2.456(4) Å, respectively, with a Co⋯Co separation of 3.601(1) Å. The structurally precedented peroxo bridged complexes, [Co₂(bpbp)(μ-O₂)(μ-RCO₂)](ClO₄)₂ (R = CH₃ or C₆H₅), are formed if a carboxylate is present. The X-ray crystal structure showed O–O and Co⋯Co distances of 1.422(3) and 3.168(1) Å, respectively, in the case of R = CH₃. ESI-MS shows that the bridging peroxo ligand is easily eliminated from [Co₂(bpbp)(μ-O₂)(μ-CH₃CO₂)]²⁺, m/z 390.0, as implicated by the observation of [Co₂(bpbp)(μ-CH₃CO₂)]²⁺, m/z 374.1, corresponding to loss of the mass equivalent of dioxygen. The superoxo complex [Co₂(bpbp)(μ-O₂)(μ-CH₃CO₂)]³⁺ can be prepared by Ce(IV) oxidation of [Co₂(bpbp)(μ-O₂)(μ-CH₃CO₂)]²⁺. Reaction of [Co₂(bpbp)(μ-H₃O₂)₂]³⁺ with hydrazine in air gives the dicobalt(II) complex [Co₂(bpbp)(NH₂NHCO₂)₂]ClO₄. In this complex the two exogenous hydrazinecarboxylato ligands are bound to individual metal ions with weak H-bonding between them as shown by X-ray structure analysis.