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

The dicobalt(III) complex, [Co-2(bpbp)(mu-H3O2)(2)](ClO4)(3) (bpbp- = 2,6-bis[bis(2-pyridylmethyl) aminomethyl]-4-tertbutylphenolate), obtained by reaction of cobalt(II) perchlorate with Hbpbp under ambient conditions contains two mu-H3O2- bridging ligands. The H-bonded O...O distances in this motif are 2.437(3) and 2.456(4) Angstrom, respectively, with a Co...Co separation of 3.601(1) Angstrom. The structurally precedented peroxo bridged complexes, [Co-2(bpbp)( (mu-O-2)(mu-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) Angstrom, respectively, in the case of R = CH3. ESI-MS shows that the bridging peroxo ligand is easily eliminated from [Co-2(bpbp)(mu-O-2)(mu-CH3CO2)](2+), m/z 390.0, as implicated by the observation of [Co-2(bpbp)(mu-CH3CO2)](2+), m/z 374.1, corresponding to loss of the mass equivalent of dioxygen. The superoxo complex [Co-2(bpbp)(mu-O-2)(mu-CH3CO2)](3+) can be prepared by Ce(IV) oxidation of [Co-2(bpbp)(mu-O-2)(mu-CH3CO2)](2+). Reaction of [Co-2(bpbp)(mu-H3O2)(2)](3+) with hydrazine in air gives the dicobalt(II) complex [Co-2(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.