A series of diamagnetic divalent nickel complexes supported by a tridentate amido diphosphine ligand [N(o-C6H4PR2)2]- ([R-PNP]-; R = Ph, i Pr, Cy) have been prepared and characterized. Deprotonation of H[Ph-PNP], H[ i Pr-PNP], and H[Cy-PNP] with n-BuLi in ethereal solutions at −35 °C produced the lithium complexes [Ph-PNP]Li(THF)2, [ i Pr-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 = i Pr, 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, [ i Pr-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, [ i Pr-PNP]NiCl, [ i Pr-PNP]NiMe, [ i Pr-PNP]Ni(n-Bu), and [Cy-PNP]NiMe are presented.

A series of nickel(II) hydride complexes supported by amido diphosphine ligands, including symmetrical [N(o-C6H4PR2)2]− ([R-PNP]−; R = Ph, i Pr, Cy) and unsymmetrical [N(o-C6H4PPh2)(o-C6H4P i Pr2)]− ([Ph-PNP- i Pr]−), have been prepared for the investigation of olefin insertion chemistry. The unsymmetrical ligand precursor H[Ph-PNP- i Pr] (1d) that features different substituents (phenyl and isopropyl) at the two phosphorus donors was prepared in 53% yield as colorless crystals. Treatment of Ni(COD)2 (COD = cycloocta-1,5-diene) with H[R-PNP] (R = Ph (1a), i Pr (1b), Cy (1c)) or 1d produced the corresponding four-coordinate nickel hydride complexes 2a−d. Attempts to isolate 2a led instead to the cyclooct-4-en-1-yl complex [Ph-PNP]Ni(η1-C8H13) (3a) as a consequence of COD insertion into the Ni−H bond of 2a. The reactions of 2a,d with ethylene, 1-hexene, and norbornene, respectively, generated cleanly the corresponding ethyl (4a,d), n-hexyl (5a,d), and 2-norbornyl (6a,d) complexes. The quantitative formation of 5a,d is indicative of exclusive 1,2-insertion of 1-hexene. In contrast, styrene inserts into the Ni−H bond of 2d in an exclusively 2,1-manner to afford [Ph-PNP- i Pr]NiCH(Me)Ph (7d) quantitatively. The selective 2,1-insertion products [Ph-PNP]NiCH(Me)CO2Me (8a), [ i Pr-PNP]NiCH(Me)CO2Me (8b), [Cy-PNP]NiCH(Me)CO2Me (8c), and [Ph-PNP- i Pr]NiCH(Me)CO2Me (8d) were also isolated from the reactions of methyl acrylate with the corresponding nickel hydride complexes 2a−d. The effects of the phosphorus and olefin substituents on the reactivity and regioselectivity of the olefin insertion reactions are discussed. In addition to solution NMR spectroscopic data for all new compounds, X-ray structures of 1d, 2b− d, 3a, and 5d− 7d are reported.

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Treatment of PdCl2(PhCN)2 with [NP]Li(THF)2 ([NP]- = N-(2-(diphenylphosphino)phenyl)-2,6-diisopropylanilide) in THF affords dimeric {[NP]PdCl}2, which reacts with tricyclohexylphosphine to produce [NP]PdCl(PCy3). The two phosphorus donors in [NP]PdCl(PCy3) are mutually cis, as indicated by the solution NMR and X-ray crystallographic studies. Both {[NP]PdCl}2 and [NP]PdCl(PCy3) are highly active catalyst precursors for Suzuki coupling reactions of a wide array of aryl halides, including those featuring electronically deactivated and sterically hindered characteristics.