Nickel(II) Complexes Containing Bidentate Amido Phosphine Ligands Derived from α-Iminophosphorus Ylides: Synthesis and Structural Characterization

The reactions of prop-2-ynyltriphenylphosphonium bromide with a series of primary aromatic or aliphatic amines in
refluxing acetonitrile generated the corresponding 2-hydrocarbylaminoprop-1-enyltriphenylphosphonium bromide
[RNHC(Me)CHPPh3]+Br- (R = 2,6-C6H3iPr2 (1a), 2,6-C6H3Me2 (1b), Ph (1c), t-Bu (1d)) as crystalline solids.
Deprotonation of 1a−d with NaH in THF at −35 °C afforded the α-iminophosphorus ylides RNC(Me)CHPPh3
(2a−d) in high yield. Spectroscopic and crystallographic data of 2 suggest a strong intramolecular interaction between
the imino nitrogen and the phosphorus atom. In contrast to N-arylated 2a−c, the N-tert-butyl-derived 2d is extremely
moisture-sensitive. Hydrolysis of 2d led to elimination of benzene and generated concomitantly the phosphine
oxide 3d that contains an ene-amine functionality. The reactions of 2a−c with Ni(COD)2 in the presence of an
excess amount of pyridine in toluene produced the divalent nickel complexes of the type [κ2-RNC(Me)CHPPh2]Ni(Ph)(Py) (4a−c). The solution and solid-state structures of these new compounds are presented.