Tetrakis(2,3,5,5-tetramethylhexen-2-yl)silane

In the title compound, C40H76Si, the Si atom is located on a special position of site symmetry -4. Thus, there is just a quarter of a molecule in the asymmetric unit. The C=C double bonds exhibit a trans configuration. The Si atom and the tert-butyl group are located on the same side of the plane formed by the C=C double bond and its four substituents. The crystal packing shows no short contacts between the molecules and despite the low crystal density (0.980 Mg m−3), there are no significant voids in the structure.

In the title compound, C 40 H 76 Si, the Si atom is located on a special position of site symmetry 4. Thus, there is just a quarter of a molecule in the asymmetric unit. The C C double bonds exhibit a trans configuration. The Si atom and the tert-butyl group are located on the same side of the plane formed by the C C double bond and its four substituents. The crystal packing shows no short contacts between the molecules and despite the low crystal density (0.980 Mg m À3 ), there are no significant voids in the structure.

Related literature
For information on the chemical background, see: Meyer-Wegner et al. (2011, 2014 This work was supported by the Beilstein Institute as part of the NanoBiC research cooperative (project eNet).

Comment
Very recently, we have investigated the reaction of Si 2 Cl 6 with NR 3 (R = Me, Et) and we have been able to show that amine-complexed dichlorosilylenes represent the key intermediates in this disproportionation reaction (Meyer-Wegner et al., 2011). In the course of these studies we isolated along with SiCl 4 the [4 + 1] cycloadduct of dichlorosilylene SiCl 2 with 2,3-dimethyl-1,3-butadiene (DMB) in good yield upon treatment of Si 2 Cl 6 with catalytic amounts of NMe 3 or NMe 2 Et in neat DMB (Meyer-Wegner et al., 2014). In this study we report on the reaction of Si 2 Cl 6 with catalytic amounts of NMe 2 Et in the presence of DMB. Subsequent treatment of this reaction mixture with tBuLi yielded the title compound (I) which could be isolated ( Fig. 1).
In the title compound ( Fig. 2), the Si centre is located on a special position of site symmtry 4. Thus, there is just a quarter of a molecule in the asymmetric unit. The C=C double bonds show a trans configuration. It is interesting to note, that the Si centre and the t-butyl group are located on the same side of the plane formed by the C=C double bond and its four substituents. The crystal packing (Fig. 3) shows no short contacts between the molecules and despite the fact that the crystal density is rather low [0.980 g/cm 3 ], there are no significant voids in the structure.

Experimental
To Si 2 Cl 6 (0.3 ml, 0.47 g, 1.74 mmol) in DMB (1.2 ml, 0.86 g, 10 mmol) a catalytic amount of NMe 2 Et (0.012 g, 0.2 mmol) was added. Subsequent treatment of this mixture with a solution of tBuLi (16 mmol) in 10 ml of pentane yielded a colorless precipitate. After filtration all volatiles were removed in vacuo. The obtained residue was dissolved in benzene.
This solution was stored at ambient temperature for a period of two days yielding single crystals of the title compound.

Refinement
H atoms were geometrically positioned and refined using a riding model with fixed individual displacement parameters [U(H) = 1.2 U eq (C) or U(H) = 1.5 U eq (C methyl )] and with C methyl -H = 0.98 Å and C methylene -H = 0.99 Å. The methyl groups attached to the double bond were allowed to rotate but not to tip.    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