Stabilization of Cobalt(I) by Tripodal π-Acceptor Ligands Py₃X (Py=2-Pyridyl; X=N, Ch, COH, P, P=O), and Preliminary Studies on the Reaction of Water and Carbon Dioxide With the Bis(ligand)cobalt(I) Complexes

Abstract

Bis ( ligand )cobalt(III/II) complexes of the tripodal π-acceptor ligands Py₃X ( Py = 2-pyridyl; X = N, CH, COH, P, P=O) have been synthesized and characterized. Electrochemical studies in acetonitrile (or propylene carbonate) solution reveal the Co^III/Co^II and Co^II/Co^I redox couples for all complexes on the cyclic voltammetric time scale; coulometry studies show the Co^I species for X = CH, P, P=O have long-term stability, while for X = N, COH the analogous complexes may be observed but are not sustained for such long periods (i.e. minutes or hours in the last two cases). Aspects relating to the stabilization of the Co^I state by these ligands are discussed. Preliminary studies on the reactivity of the bis(ligand)cobalt(I) species (X = CH, P) with water and HCO₃^- are also reported: water undergoes reduction to H₂ but no reduction of HCO₃^- occurs. In the water reduction reaction involving the complex with X = P, ligand dissociation does not occur, in contrast to the case for X = CH and for the analogous reaction of [Co( bpy )₃]⁺.