Monomeric Phosphido and Phosphinidene Complexes of Nickel

An unusual family of three-coordinate, d⁸ and d⁹ nickel phosphido and phosphinidene complexes containing the chelating 1,2-bis(di-tert-butylphosphino)ethane (dtbpe) ligand and a terminal PR₂^- or PR^2- ligand have been prepared. The complexes (dtbpe)Ni{P(t-Bu)₂} (2), [(dtbpe)Ni{P(t-Bu)₂}⁺][PF₆^-] (3), [(dtbpe)Ni{P(H)(dmp)}⁺][PF₆^-] (5), and (dtbpe)Ni{P(dmp)} (6) have been structurally characterized by single-crystal X-ray diffraction methods. The three-coordinate d⁸ complexes exhibit Ni−P bond lengths and ligand geometries that indicate they participate in symmetry-allowed ligand-to-metal π bonding involving phosphorus p-electrons and a metal-orbital of π symmetry that lies in the Ni coordination plane. Compound 6 is a rare example of a late-transition-metal terminal phosphinidene complex.