Crystal structure and molecular stereochemistry of a five-co-ordinate π-allyl complex of nickel: π-methallyl[bis-1,2-(diphenylphosphino)ethane]nickel bromide

Abstract

The crystal and molecular structure of π-methallyl[bis-1,2-(diphenylphosphino)ethane]nickel bromide, π-(CH₂·CMe·CH₂)Ni(Ph₂P·[CH₂]₂·PPh₂)Br, has been determined by X-ray diffraction techniques. The complex crystallizes in the centrosymmetric triclinic space group P(C_i¹; No. 2), the reduced cell parameters being a= 11·135 ± 0·010, b= 8·171 ± 0·009, c= 15·408 ± 0·019 Å, α= 90·81 ± 0·10, β= 96·58 ± 0·10, γ= 105·78 ± 0·10°, Z= 2. Data in the range 8°⩽ 2θ⩽ 46°(Mo-K_α radiation) were collected with a Buerger automated diffractometer. All non-hydrogen atoms were located by Patterson and Fourier methods and the structure refined by least-squares techniques to R 10·1% for 2732 independent non-zero reflections. The complex is the first five-co-ordinate π-allylnickel species to be examined crystallographically. The central nickel atom has a square-pyramidal stereochemistry with the chelating bis-1,2-(diphenylphosphino)ethane ligand and the formally bidentate π-methallyl ligand each occupying two cis basal sites. The apical co-ordination position is occupied by a bromine atom (Ni–Br 2·671 ± 0·002 Å). Non-planarity of the π-methallyl ligand and the unusually long Ni–Br bond are discussed.