REACTIVITY OF NICKEL(II) DIPHOSPHINE COMPLEXES TOWARDS ALKOXIDES - A NEW ROUTE TO THE SYNTHESIS OF NICKEL(0) COMPOUNDS THROUGH NICKEL(II) ALKOXIDES

Reaction of [Ni(L-L)Cl2] [L-L = Ph2P(CH2)nPPh2, n = 2 (dppe) or 3 (dpp p)] with NaOR (R = Me, Et or Pr(i)) under a dinitrogen atmosphere affo rded [Ni(L-L)2], Ni(OR)2 and aldehyde (or acetone when R = Pr(i)) in 1 : 1 : 1 ratio, showing the peculiar reducing effect of alkoxide promo ted by the chelating property of the phosphorus ligand. The reaction o f NaOMe with [Ni(dcpe)Cl2] [dcpe = 1,2-bis(dicyclohexylphosphino)ethan e] afforded mainly [Ni2(dcpe)3] when carried out in the absence of fre e diphosphine, and [Ni(dcpe)2] in the presence of free diphosphine. Th e reaction always yields the nickel(o) species [Ni(L-L)(CO)2] when it is carried out under a carbon monoxide atmosphere. The intermediate fo rmation of unstable alkoxo(diphosphine)nickel(II) complexes has been d emonstrated by recording the P-31 NMR spectra of the reacting solution s at low temperature; in the case of the reaction of [Ni(dcpe)Cl2] wit h NaOMe only, it was possible to isolate as a solid the [Ni(dcpe)(OMe) 2] Complex, which has been fully characterized by analytical and spect roscopic (IR and H-1, P-31 NMR) methods. A possible route by which nic kel(o) complexes could be formed is discussed.