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

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