DICATIONIC NICKEL(II) CARBONYL-COMPLEXES CONTAINING TETRADENTATE LIGANDS

This article describes the preparation and spectroscopic characterizat ion of three dicationic Ni(II) carbonyl complexes containing tripodal tetradentate ligands. An X-ray diffraction study of [Ni(PP(3)E)(CO)](B F4)(2) (where PP(3)E is tris(2-(diethylphosphino)ethyl)phosphine) has been completed and confirms a trigonal bipyramidal structure with an a pical carbonyl ligand. The binding of CO is weak and reversible. The s tability of these complexes is enhanced by the small chelate bite impo sed by the tetradentate ligands. The electrochemical behavior of these complexes depends on the nature of the donor atom trans to CO. The [N i(NP(3)E)(CO)](2+) (where NP(3)E is tris(2-(diethylphosphino)ethyl)ami ne) cation undergoes two reversible one-electron reductions, whereas t he corresponding tetraphosphine cations undergo irreversible two-elect ron reductions.