Nickel(II) Complexes Containing Bidentate Diarylamido Phosphine Ligands

Abstract

A series of diamagnetic divalent nickel complexes supported by bidentate diarylamido phosphine ligands have been prepared and characterized. Deprotonation of N-(2-diphenylphosphinophenyl)-2,6-diisopropylaniline (H[iPr-NP]) and N-(2-diphenylphosphinophenyl)-2,6-dimethylaniline (H[Me-NP]) with n-BuLi in THF at −35 °C produced the corresponding lithium complexes, [iPr-NP]Li(THF)2 and [Me-NP]Li(THF)2, respectively. The chloride complex {[iPr-NP]NiCl}2 is accessible from the reaction of NiCl2(DME) with [iPr-NP]Li(THF)2 or H[iPr-NP] in the presence of triethylamine. Addition of PMe3 to {[iPr-NP]NiCl}2 afforded [iPr-NP]NiCl(PMe3), from which [iPr-NP]NiMe(PMe3), [iPr-NP]NiPh(PMe3), and [iPr-NP]Ni(η3-CH2Ph) were prepared from the metathetical reactions with appropriate Grignard reagents. Solution NMR data of [iPr-NP]NiMe(PMe3) revealed two geometric isomers at room temperature with the major species carrying PMe3 cis to the phosphorus donor of the amido phosphine ligand. Interestingly, only one of the possible isomers is observed for [iPr-NP]NiCl(PMe3) and [iPr-NP]NiPh(PMe3), in which the two phosphorus donors in the former are exclusively cis whereas those in the latter are trans. The benzyl complexes [iPr-NP]Ni(η3-CH2Ph) and [Me-NP]Ni(η3-CH2Ph) are prepared directly from the reactions of [iPr-NP]Li(THF)2 and [Me-NP]Li(THF)2, respectively, with Ni(COD)2 in the presence of benzyl chloride. The η3-feature of the benzyl ligand maintained in solution is elucidated by the 1JCH value observed for the benzylic methylene group in the NMR spectroscopy. In addition to the spectroscopic data for all new molecules, X-ray structures of H[iPr-NP], [Me-NP]Li(THF)2, [iPr-NP]NiCl(PMe3), [iPr-NP]NiMe(PMe3), [iPr-NP]NiPh(PMe3), [iPr-NP]Ni(η3-CH2Ph), and [Me-NP]Ni(η3-CH2Ph) are presented.