(E)-N,N′-Bis(2,6-dimethylphenyl)-N,N′-bis(trichlorosilyl)ethylene-1,2-diamine

The asymmetric unit of the title compound, C18H20Cl6N2Si2, contains one half of the centrosymmetric molecule. The two benzene rings are perpendicular to the plane of Si–N–C=C–N–Si fragment, making a dihedral angle of 89.9 (1)°. The crystal packing exhibits short intermolecular Cl⋯Cl contacts of 3.3119 (17) Å.

The asymmetric unit of the title compound, C 18 H 20 Cl 6 N 2 Si 2 , contains one half of the centrosymmetric molecule. The two benzene rings are perpendicular to the plane of Si-N-C C-N-Si fragment, making a dihedral angle of 89.9 (1) . The crystal packing exhibits short intermolecular ClÁ Á ÁCl contacts of 3.3119 (17) Å .

Experimental
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CV2522). The title compound, (I), was synthesized by the reaction of the excess silicon tetrachloride and the dilithium salt of the diimine [N(2,6-Me 2 C 6 H 3 )C(H)] 2 in THF (Haaf et al., 1998). A high yielding preparation of the title compound was devised whereby two equivalents of SiCl 4 were treated with dilithium salt in THF (Baker et al., 2008). The title compound and related compounds are of interest in silylene chemistry in relation to synthesis of the silylene dichloride precursor (Haaf et al., 2000;Baker et al., 2008).
The title molecule ( Fig. 1) exists in an E configuration with respect to the C═C double bond (Table 1) (Haaf et al., 1998), because of E configuration.

S2. Experimental
All manipulations were carried out under an argon atmosphere using standard Schlenk techniques or a nitrogen-filled glovebox. Solvents (THF, toluene) were dried over sodium and freshly distilled prior to use. Naphthalene (1.24 g,10 mmol) was dissolved in THF (15 ml) and lithium powder (71 mg, 10 mmol) added. The resultant suspension was stirred at room temperature for 4 h to give an green suspension. [N(2,6-Me 2 C 6 H 3 )C(H)] 2 (1.17 g, 4.5 mmol) was added to the suspension after cooled to -78 o C. The resultant mixture was stirred at room temperature for 24 h to give a red solution. At -78 o C, silicon tetrachloride (10 ml, 88 mmol) was added to the solution. Warmed to room temperature and stirred for 24 h. Volatiles were removed in vacuo and the residue was extracted with toluene (20 ml).

S3. Refinement
All H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C-H of 0.93-0.96 Å, and U iso (H) = 1.2-1.5 U eq (C).  The molecular structure of (I) showing 30% probability displacement ellipsoids and the atom-numbering scheme. The unlabelled atoms are related with the labelled ones by symmetry operation (-x, -y + 2, -z). H atoms omitted for clarity. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq  (7)