Amido Pincer Complexes of Nickel(II): Synthesis, Structure, and Reactivity
datasetposted on 13.03.2006, 00:00 by Lan-Chang Liang, Pin-Shu Chien, Jia-Ming Lin, Mei-Hui Huang, Yu-Lun Huang, Ju-Hsiou Liao
A series of diamagnetic divalent nickel complexes supported by a tridentate amido diphosphine ligand [N(o-C6H4PR2)2]- ([R-PNP]-; R = Ph, iPr, Cy) have been prepared and characterized. Deprotonation of H[Ph-PNP], H[iPr-PNP], and H[Cy-PNP] with n-BuLi in ethereal solutions at −35 °C produced the lithium complexes [Ph-PNP]Li(THF)2, [iPr-PNP]Li(solv) (solv = THF, Et2O), and [Cy-PNP]Li(solv) (solv = THF, Et2O), respectively. The reactions of [R-PNP]Li(solv)n with NiCl2(DME) in THF at −35 °C generated [R-PNP]NiCl, which was then reacted with a variety of Grignard reagents to afford the corresponding hydrocarbyl complexes [R-PNP]NiR‘ (R = Ph, R‘ = Me, Et, n-Bu, i-Bu, n-hexyl, CH2SiMe3, Ph; R = iPr, R‘ = Me, Et, n-Bu; R = Cy, R‘ = Me, Et, n-Bu). Of particular interest among the compounds isolated are alkyl complexes that contain β-hydrogen atoms. Treatment of the hydrocarbyl complexes with halogenated hydrocarbons such as dichloromethane, benzyl bromide, and phenyl iodide produced the corresponding nickel halide derivatives. The chloride complexes [Ph-PNP]NiCl, [iPr-PNP]NiCl, and [Cy-PNP]NiCl are all active catalyst precursors for Kumada coupling reactions, including those of alkyls containing β-hydrogen atoms. In addition to spectroscopic data for all new compounds, X-ray structures of [Cy-PNP]Li(OEt2), [Ph-PNP]NiCl, [Ph-PNP]NiBr, [Ph-PNP]NiMe, [Ph-PNP]Ni(n-Bu), [Ph-PNP]NiCH2SiMe3, [iPr-PNP]NiCl, [iPr-PNP]NiMe, [iPr-PNP]Ni(n-Bu), and [Cy-PNP]NiMe are presented.