Oxidation-Induced Ligand Swap: Oxygen Insertion into a Cobalt-Phosphine Complex

The synthesis and characterization of a half-sandwich cobalt(II) complex supported by a bidentate, pendent-amine phosphine ligand (PPh2NBn2 = 1,5-diaza-3,7-diphosphacyclooctane) are reported. Oxidation of a cobalt(I)-phosphine precursor with silver(I) salts yielded the paramagnetic complex [CpCo(PPh2NBn2)]+. This species rapidly reacts with oxygen upon air exposure under ambient conditions, resulting in the insertion of oxygen into the cobalt-phosphine bonds. Two cobalt complexes were generated from this reaction: the cobaltocenium cation, bearing two Cp ligands (Cp = cyclopentadienyl); and a cobalt(II)-bis(phosphine oxide) dicationic complex in which two O2P2N2 ligands coordinate in a fac fashion via two oxygen and one nitrogen centers to establish an overall octahedral geometry. Thus, the aerobic oxidation of the phosphine induces the exchange and rearrangement of the ligands at cobalt.