Chloridobis{N-[(dimethylamino)dimethylsilyl]-2,6-dimethylanilido-κ2 N,N′}titanium(III)

In the monomeric title titanium(III) compound, [Ti(C12H21N2Si)2Cl], the metal atom is surrounded by two N–silylated anilide ligands in an N,N′′-chelating mode. The two ends of the N—Si—N chelating unit exhibit different affinity to the metal center. The Ti—Namine bond is longer than the Ti—Nanilide bond by about 0.29 Å. The two ligands are arranged trans to each other and the molecule demonstrates a pseudo-twofold rotation along the axis of the Ti—Cl bond. The five–coordinate Ti atom demonstrates a highly distorted trigonal-bipyramidal geometry.


Comment
Group 4 metal amides supported with the N-silylated anilido ligands were active catalysts for olefin polymerization (Gibson et al., 1998;Hill & Hitchcock, 2002). In particular, titanium amides were found to be more efficient and applicable (Alesso et al., 2008;Oakes et al., 2004;Tabernero et al., 2009). Therefore, the monoionic N-silylated anilido ligand bearing a pendant amino group was employed for synthesizing titanium compound. Analogous compounds with different metals including Zn (Schumann et al., 2000), Zr (Chen, 2009) and Fe (Chen, 2008) have been synthesized. Moreover, a group of zirconium amides with the similar ligand were reported showing good performance in ethylene polymerization (Yuan et al., 2010). It implied that the title titanium compound would behave better in catalysis application.
It is interesting that the valence of Ti has changed from IV to III. Similar situation could be found in Ovchinnikov's work (Ovchinnikov et al., 1993) and other - Chomitz et al., 2008). The driving factors for reduction will be investigated in further research. The suitable single-crystal of the title compound was obtained by recrystallization in toluene. Its molecular structure is shown in Fig. 1. In the monomeric molecular structure of title compound, the metal center is coordinated by two N-silylated anilido ligands. Each ligand has an N-Si-N chelating moiety, which is presumed to be a "quasi" conjugated unit owing to d···π-interaction between Si and N atoms. Two ligands are arranged in trans-to each other and obey the pseudo-C 2 symmetrical operation. Such arrangement makes Ti atom right in the triangular planes of N1···N3···Cl1 and N2···N4···Cl1. The five-coordinate Ti(III) center demonstrates a highly distorted trigonal-bipyramid geometry (N2-and N4-apical atoms). The configuration is as same as the Fe(III) compound reported previously (Chen, 2008), presumably due to the same valence. The metal center Ti is chelated with an average N-Ti-N bite angle of 74.18 (13)°. The corresponding N-Si-N of the ligand is constrained to be about 95.25 (16)°. The mean Ti-N anilido bond is 1.992 (3)Å, whereas the mean Ti-N amino bond is 2.286 (4)Å in the title compound. It suggests the former is much tighter than the latter. They are different from corresponding bond lengths 1.972 (4)Å and 2.356 (6)Å in a related amido Ti(III) compound reported by Chomitz et al. (2008).

Experimental
TiCl 4 (THF) 2 (0.48 g, 1.45 mmol) was added into the solution of [LiN(SiMe 2 NMe 2 )(2,6-Me 2 C 6 H 3 )] 2 (0.66 g, 1.45 mmol) in Et 2 O (30 ml) at 273 K. The reaction mixture was warmed to room temperature and kept stirring for 12 h. It was dried in vacuum to remove all volatiles and the residue was extracted with CH 2 Cl 2 (30 ml). Concentration of the filtrate under reduced pressure and recrystallization in toluene gave the title compound as purple crystals (yield 0.50 g, 66%).

Refinement
The methyl H atoms were constrained to an ideal geometry, with C-H distances of 0.97Å and U iso (H) = 1.5U eq (C), but each group was allowed to rotate freely about its C-C, C-N and C-Si bonds. The other H atoms were placed in geometrically supplementary materials sup-2 idealized positions and constrained to ride on their parent atoms, with C-H distances in the range 0.94Å and U iso (H) = 1.2U eq (C). Fig. 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.

Figures
Crystal data [Ti(C 12