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-l-enyltriphenylphosphonium bromide [RNHC(Me)=CHPPh3]Br-+(-) (R = 2,6-(C6H3Pr2)-Pr-i (1a), 2,6-C6H3Me2 (1b), Ph (1c), t-Bu (1d)) as crystalline solids. Deprotonation of 1a-d with NaH in THF at -35 degrees C afforded the alpha-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-ted-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 [kappa(2)-RNC(Me)= CHPPh2]-Ni(Ph)(Py) (4a-c). The solution and solid-state structures of these new compounds are presented.