Structure and properties of cis-bis(dicyclohexylphosphine)dihalogeno-nickel(II) complexes

Abstract

Dicyclohexylphosphine and tetracyclohexyldiphosphane both react with anhydrous nickel(II) chloride and bromide to form the same type of complex in either case, namely cis-[NiX₂{P(C₆H₁₁)₂H}₂](X = Cl or Br). This has been confirmed in the solid state by X-ray diffraction and in solution by ¹H and ³¹P n.m.r. spectroscopy. Other spectro-scopic data, as well as melting points, molecular weights, and elemental analyses, are also compatible with this conclusion. Evidence for a trans isomer of the bromide in solution is also observed. No evidence for the formation of a three-membered chelate ring in the reactions with the diphosphane could be detected. The ³¹P chemical shifts in CH₂Cl₂, are 36.4 (20 °C, 0.2 mol dm^–3) and –46.1 and –30.5 p.p.m. (0 °C, 0.2 mol dm^–3) for cis-[NiCl₂{P(C₆H₁₁)₂H}₂], cis-[NiBr₂{P(C₆H₁₁)₂H}₂], and trans-[NiBr₂{P(C₆H₁₁)₂H}₂] respectively, relative to 85% H₃PO₄. The complexes exhibit strong P–H coupling due to the secondary phosphine proton. X-Ray diffraction shows that cis-[NiCl₂{P(C₆H₁₁)₂H}₂] crystallizes in the tetragonal space group /4₁/a(No. 88) with a= 20.69(1) and b= 25.15(2)Å, and Z= 16. The structure was solved, using Weissenberg methods and the heavy-atom technique from 1400 independent reflections using Cu-K_α radiation, to R′ 0.118. The nickel atom is 0.05 Å from the plane formed by the chlorine and phosphorus atoms. The average Ni–Cl distance IS 2.20(1)Å and the average Ni—P distance is 2.15(l)Å.