Dicationic nickel(II) carbonyl complexes containing tetradentate ligands

This article describes the preparation and spectroscopic characterization of three dicationic Ni(II) carbonyl complexes containing tripodal tetradentate ligands. An X-ray diffraction study of [Ni(PP(3)E)(CO)](BF4)(2) (where PP(3)E is tris(2-(diethylphosphino)ethyl)phosphine) has been completed and confirms a trigonal bipyramidal structure with an apical carbonyl ligand. The binding of CO is weak and reversible. The stability of these complexes is enhanced by the small chelate bite imposed by the tetradentate ligands. The electrochemical behavior of these complexes depends on the nature of the donor atom trans to CO. The [Ni(NP(3)E)(CO)](2+) (where NP(3)E is tris(2-(diethylphosphino)ethyl)amine) cation undergoes two reversible one-electron reductions, whereas the corresponding tetraphosphine cations undergo irreversible two-electron reductions.