Crystal Structure of ((C 6 H 11 ) 2 N) (C 6 H 12 N) 2 SiH

The structure of the mixed tri(amino)silane has been determined by in the solid state. The compound crystallized in the monoclinic form. The crystallographic data of the compound is given in Table 1. A list of bond lengths and angles are Table 2. The refinement converged to a final R value of 0.0649 and wR= 00687 with weighting schemes based on counting statistics, where W = 0.00659. Fin: (shift/esd), maz =0.096. The molecular parameters obtained are Si1– N1 =1.712 Å (4) Si1 - N2=1.707 Å (4), Si-N3=1.717 Å (4), ˂N2 - Sil - N3=109.6(2), ˂N1 - Sil - N3=116.0(2), ˂ N1 - Sil - N2= 107.0(2).


Introduction:
Silicon -nitrogen compounds have gained a lot of importance.The Si-X bond is of particularly great importance in the chemistry of organosilicon compounds as almost all organosilicon compounds are ultimately obtained from elementary silicon through halides of silicon, SiCl4, SiHCl3.The Si-X bond is much more reactive than the C-X bond toward polar reagents [1,2].There are only a few synthetic methods to prepare these compounds [3,4].Single crystals of this compound were obtained by the slow crystallization of the liquid obtained after removal of the major portion of the solvent mixture at room temperature.This compound was found to be highly sensitive to moisture.Hence, the crystal was mounted in a lindemann capillary for data collection.The characterisation of this mixed tri(cyclo)silane has been done by using x-ray crystallography.Complete set of data was collected using Mo-Kα radiation.

Experiments:
The compound was prepared by transamination reaction [5] by taking tris(dicyclohexylamino)silane and hexamethyleneimine ( 1:2 ratio).50 ml of 1:1 (v/v) benzene n-hexane solvent mixture was taken in a dry 250 ml side arm flask was flushed with dry, oxygen free nitrogen and stirred vigorously for 24 hours.As soon as the addition started a slight exothermic action took place.The solid products product formed was purified by repeated washing with n-hexane.A small portion of the sample were used for characterisation by 29 Si NMR [5], 15 N NMR Fig. 2 and FT-IR.The crystal was colourless and transparent.Crystallographic data of the compound is given in Table .1.Full lists of positional and thermal parameters, bond distances (Table 3) and bond angles are given (Table 4)      An ORTEP view of the molecule is shown in Fig. 1.The structure consists of one silicon atom in a tetracoordinate state bonded to three nitrogen atoms and one hydrogen atom.Two nitrogen atoms out of three, form a part of two cyclic seven membered ring and the other nitrogen atom is exocyclic with two cyclohexane rings.Here also the nitrogen atoms NI, N2 and N3 deviate from the plane by 0.201 Å (4), 0.082 Å (4) and 0.128 Å (3) respectively.These values indicate that in this molecule the nitrogen atoms are slightly more pyramidal than that reported earlier [9], where the substituents are less bulky, as reflected by the angles (total angles around the nitrogen atoms are N1 = 355.0°(11),N2 =359.2°(15) and N3 = 358(9) Table 4 .Various silicon-nitrogen bond lengths (Table3) indicate that one of the bond is marginally shorter (S1-N2) than the other two and also these bonds are slightly longer than that of the less sterically hindered amino group.This provides an evidence for the fact that in bulkier systems the silicon-nitrogen bond is slightly weaker [8,9].The various C-C bond lengths are the range of 1.47 Å and do not exhibit much deviation as expected.As a result nitrogen atom N2 can be slightly deshielded when compared to the other two nitrogen atoms, which interact with each other as can be seen from the Fig. 2. But in this compound, probably the interaction of the hydrogen attached to the silicon is slightly reduced, as can be seen from the Newman projection diagram and as a result only two signals are obtained for this compound in its 15 N NMR spectrum.(Fig. 3).15NNMR (40.56 MHz) spectrum of (C6H11)2N)(C6H12N)2SiH in paraffin.H} 15 N of the hexamethyleneimine and dicyclohexylamine which resonates at -338.9 and -306.5 ppm respectively [6].But in the present study, nitrogen atoms show resonances at -343.4 and 313.7ppm.These peaks can be assigned due to the fact that one of the nitrogen N2, which is a part of the seven membered ring, (is having conjugation with σ* Si-H bond) is deshielded when compared to the parent amine (-338.9ppm).Whereas, the other two nitrogen atoms are having mutual interactions and as a result they resonate at -343.4 ppm.In the present study when the nitrogen becomes slightly non-planar, the (p-d)π interaction will be slightly decreased.This is evident from the comparatively longer bond length in this compound.Crystallographic data as well as spectroscopic studies (data given in Table 3,4) provide evidence for this observation.

Conclusion
In this study there is a small increment in Si-N bond length (1.71 Å), deshielding of the Si-H hydrogen (∂= 4.34 ppm) and small increase in Si-H stretching frequency (ѵSi-H 2122 cm -1 ).From the Newman projection it is clear that the orientation of the lone pair on N2 with σ* Si-H bond is slightly less than 180 0 .Even though the shift is not a significant one.Thereby showing a small decrease in conjugation of lone pair on N2 with σ* Si-H bond.This may be the reason for the marginal increment of Si-H frequency along with mild desheilding of the Si-H protons.

An
ORTEP view of the full molecule is shown Fig.1.

Fig: 2 Fig. 2 .
Fig:2 Fig.2.shows the Newman projection diagrams of compound and where the lone pair on N2 overlap with σ*Si-H.N1 and N3 lone pairs overlap with σ*Si-N3 and o* Si-NI respectively.As a result nitrogen atom N2 can be slightly deshielded when compared to the other two nitrogen atoms, which interact with each other as can be seen from the Fig.2.But in this compound, probably the interaction of the hydrogen attached to the silicon is slightly reduced, as can be seen from the Newman projection diagram and as a result only two signals are obtained for this compound in its 15 N NMR spectrum.(Fig.3).15NNMR (40.56 MHz) spectrum of (C6H11)2N)(C6H12N)2SiH in paraffin.

Table 2
The 29 Si, 15 N chemical shift along with Si-H vibrational frequencies are given below

Table 3
Lists of bond lengths 1