5-COORDINATION .11. NICKEL(2) COMPLEXES OF CIS-1,2-BIS(DIPHENYLPHOSPHINO)ETHYLENE

cis-1,2-Bis(diphenylphosphino)ethylene forms five-coordinate, diamagnetic [Ni(ligand)2X]B(C6H5)4 (X = Cl, Br, I) complexes, as well as the diamagnetic, four-coordinate [Ni(ligand)X2] (X = C1, Br, I, NCS) complexes. The compounds were characterized by conductivity and magnetic measurements, electronic and infrared spectra, and elemental analyses. The electronic spectra of the five-coordinate complexes differ considerably from known trigonal-bipyramidal complexes and are assigned a square-pyramidal structure. The donor properties of the ethylenc-diphosphine ligand are compared with those of its saturated analog, bis(diphenylphosphino)ethane, and the differences in the types of complexes formed are discussed in terms of π bonding and steric requirements of the ligand. © 1969, American Chemical Society. All rights reserved.