Terminal nickel(ii) amide, alkoxide, and thiolate complexes containing amido diphosphine ligands of the type [N(o-C6H4PR2)2]- (R = Ph, (i)Pr, Cy).

A series of nickel(ii) complexes of the type [R-PNP]Ni(ER') ([R-PNP](-) = [N(o-C(6)H(4)PR(2))(2)](-); R = Ph, (i)Pr, Cy; E = NH, O, S; R' = Ph, (t)Bu) featuring unsupported, covalently bound pi-donor ligands have been prepared and characterized. The metathetical reactions of [R-PNP]NiCl (R = Ph, (i)Pr, Cy) with LiNHPh, NaOPh, or NaSPh, respectively, produced the corresponding anilide [R-PNP]Ni(NHPh), phenolate [R-PNP]Ni(OPh), and thiophenolate [R-PNP]Ni(SPh) derivatives. Treatment of [Ph-PNP]NiCl with either LiNH(t)Bu or NaO(t)Bu generated tert-butyl amide [Ph-PNP]Ni(NH(t)Bu) and tert-butoxide [Ph-PNP]Ni(O(t)Bu), respectively. In contrast, attempts to prepare analogous tert-butyl amide and tert-butoxide complexes of [(i)Pr-PNP](-) or [Cy-PNP](-) were not successful. Protonolysis studies of these nickel(ii)-heteroatom complexes revealed the basic reactivity of these pi-donor ligands. The basicity follows the order NH(t)Bu > O(t)Bu > NHPh > OPh > SPh. In addition to solution NMR spectroscopic data for all new compounds, X-ray structures of [(i)Pr-PNP]Ni(NHPh) and [(i)Pr-PNP]Ni(OPh) are presented.

Intermolecular arene C-H activation by nickel(II).

Intermolecular arene C-H activation mediated by a divalent nickel species under extremely mild conditions is described. The reactions of either Ni(COD)2 with H[N(o-C6H4PR2)2] (H[R-PNP]; R = iPr, Cy) in benzene at room temperature or [R-PNP]NiCl with LiBHEt3 in THF at -35 degrees C produced the corresponding [R-PNP]NiH in high yield. Addition of 1 equiv of B(C6F5)3 to a benzene solution of [R-PNP]NiH at room temperature led to the formation of a mixture that contains [R-PNP]NiPh and [R-PNP]Ni(C6F5), both of which are proposed to evolve from zwitterionic [R-PNP]Ni(mu-H)B(C6F5)3. In contrast, the reaction of [R-PNP]NiH with AlMe3 in benzene at room temperature afforded exclusively the corresponding [R-PNP]NiPh. Similar results were also observed for intermolecular toluene and m-xylene C-H activation by [R-PNP]NiH. A parallel study involving [R-PNP]NiMe (R = Ph, iPr, Cy) on the reactivity of intermolecular arene activation reveals the significance of pi basicity of Ni(II) in these molecules. The remarkable reactivity of inexpensive Ni(II) species established in this study is attractive, particularly from an economic viewpoint, as compared to the current alternatives of 4d and 5d metals.

Zirconium and hafnium complexes containing bidentate diarylamido-phosphine ligands.

The first examples of mononuclear, structurally characterized triarylphosphine complexes of zirconium and hafnium are reported. The metathetical reactions of MCl4(THF)2 (M = Zr, Hf) with [iPrNP]Li(THF)2 ([iPrNP]- = N-(2-(diphenylphosphino)phenyl)-2,6-diisopropylanilide) or [MeNP]Li(THF)2 ([MeNP]- = N-(2-(diphenylphosphino)phenyl)-2,6-dimethylanilide) in toluene at -35 degrees C produced the corresponding [iPrNP]MCl3(THF) and [MeNP]2MCl2, respectively, in high yield. In contrast, attempts to prepare [MeNP]MCl3(THF) and [iPrNP]2MCl2 led to the concomitant formation of mono- and bis-ligated complexes, from which purification proved rather ineffective. The solution and solid-state structures of [iPrNP]MCl3(THF) and [MeNP]2MCl2 were studied by multinuclear NMR spectroscopy and X-ray crystallography. The geometry of these six-coordinate complexes is best described as a distorted octahedron in which the chloride ligands in [iPrNP]MCl3(THF) adopt a virtually meridional coordination mode whereas those in [MeNP]2MCl2 are trans to each other.