Bis{N-[(diethylamino)dimethylsilyl]anilinido-κ2 N,N′}nickel(II)

The mononuclear NiII amide, [Ni(C12H21N2Si)2], has the NiII atom N,N′-chelated by the N-silylated anilinide ligands. The ligands are arranged cis to each other and obey the C 2-symmetry operation. The two ends of the N—Si—N chelating unit exhibit different affinities for the metal atom: the Ni—Nanilinide bond length is 1.913 (3) Å and Ni—Namine is 2.187 (3) Å. The four-coordinate NiII ion demonstrates a distorted tetrahedral geometry.


Juan Chen and Jing Li Comment
Metal amides were important substitutes for cyclopentadienyl derivatives and were found to have valuable applications in various industrial and biological processes (Holm et al., 1996;Kempe, 2000). Group 4 metal amides with the N-silylated anilinide ligands were active catalysts for olefin polymerization (Gibson et al., 1998;Hill & Hitchcock, 2002). Our research interest focused on N-silylated anilinide ligands bearing a pendant amino group. Analogous compounds with different metals including Zn (Schumann et al., 2000), Zr (Chen, 2009) and Fe (Chen, 2008) have been synthesized and the zirconium compounds were reported showing good performance in ethylene polymerization (Yuan et al., 2010).
Recently, a kind of bidentate N-donor ligand supported nickel complex activated by MAO was used as a catalyst conducting longstanding living ethylene polymerization (Zai et al., 2010). In view of the importance of these compounds, the synthesis and crystal structure of a new nickel(II) anilinide complex is reported.
The title compound was prepared by one-pot reaction of LiBu n , N-[(diethylamino)dimethylsilyl]aniline and NiCl 2 . It is monomeric and the ligand has an N-Si-N chelating group. It is presumed that the empty d-orbitals on silicon would interact with the lone-pair electrons on the p-orbital of nitrogen center through a d···pπ interaction, resulting in a "quasi" conjugated N-Si-N motif. Compared with rigid N-C-N chelating unit in the amidinate ligand, the N1-Si1-N2 chelating group is much flexible. The Ni center is fixed by two ligands. Each ligand bites the center with an N1-Ni1-N2 angle of 77.82 (11)°. As biting the metal center, the angle of N1-Si1-N2 is constrained to be 95.28 (13)°. The two ends of the N-Si-N chelating unit exhibit different affinities for the metal center. Ni-N anilinide bond is 1.913 (3) Å and Ni-N amino bond is 2.187 (3)Å. The coordinate geometry of N anilinide atom is trigonal planar (sum of three angles around it being 359°). Both distances of Si1-N1 (1.699 (3)Å) and N1-C1 (1.375 (4)Å) are short. It suggests a certain degree delocalization of the lone-pair electron density from the p-orbital of N1 to the π-orbital of the phenylsubstituent. The two ligands around the Ni atom are arranged cis to each other and obey the C 2 symmetry operation. The four-coordinate Ni atom demonstrates a distorted tetrahedral geometry.

Experimental
A solution of LiBu n (1.6 M, 1.9 ml, 3.0 mmol) in hexane was slowly added into a solution of N-[(diethylamino)dimethylsilyl]aniline (0.67 g, 3.0 mmol) in THF (20 ml) at 273 K by syringe. The mixture was stirred at room temperature for two hours and then added to a stirring suspension of NiCl 2 (0.20 g, 1.5 mmol) in THF (20 ml) at 273 K. The resulting mixture was stirred at room temperature for 8 h. Then all the volatiles were removed under vacuum. The residue was extracted with toluene (25 ml). The filtrate was concentrated to give the title compound as red crystals (yield 0.39 g, 52%

Refinement
The methyl H atoms were constrained to an ideal geometry, with C-H distances of 0.96Å and U iso (H) = 1.5U eq (C), but each group was allowed to rotate freely about its C-C and C-Si bonds. The methylene H atoms were constrained with C -H distances of 0.97Å and U iso (H) = 1.2U eq (C). The phenyl H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H distances in the range 0.93Å and U iso (H) = 1.2U eq (C).

Figure 1
The molecular structure, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms are presented as a small spheres of arbitrary radius. Symmetry codes: (i) -x+3/2, -y+1/2, z.  (17) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cells.u.'s is used for estimating s.u.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.