Reactivity of nickel (II) diphosphine complexes towards alkoxides: a new route to the synthesis of nickel(0) compounds through nickel(II) alkoxides

Abstract

Reaction of [Ni(L–L)Cl₂][L–L = Ph₂P(CH₂)_nPPh₂, n= 2(dppe) or 3 (dppp)] with NaOR (R = Me, Et or Prⁱ) under a dinitrogen atmosphere afforded [Ni(L–L)₂], Ni(OR)₂ and aldehyde (or acetone when R = Prⁱ) in 1 :1 :1 ratio, showing the peculiar reducing effect of alkoxide promoted by the chelating property of the phosphorus ligand. The reaction of NaOMe with [Ni(dcpe)Cl₂][dcpe = 1,2-bis(dicyclohexylphosphino)-ethane] afforded mainly [Ni₂(dcpe)₃] when carried out in the absence of free diphosphine, and [Ni(dcpe)₂] in the presence of free diphosphine. The reaction always yields the nickel(0) species [Ni(L–L)(CO)₂] when it is carried out under a carbon monoxide atmosphere. The intermediate formation of unstable alkoxo(diphosphine)nickel(II) complexes has been demonstrated by recording the ³¹P NMR spectra of the reacting solutions at low temperature; in the case of the reaction of [Ni(dcpe)Cl₂] with NaOMe only, it was possible to isolate as a solid the [Ni(dcpe)(OMe)₂] complex, which has been fully characterized by analytical and spectroscopic (IR and ¹H, ³¹P NMR) methods. A possible route by which nickel(0) complexes could be formed is discussed.