Aminosilanes derived from 1H-benzimidazole-2(3H)-thione

In two trimethylsilyl-substituted 1H-benzimidazole-2(3H)-thiones, noncovalent C—H⋯π interactions between the centroid of the benzmidazole system and the SiMe3 groups form helicoidal arrangements in one, and dimerization results in the formation of (8) rings via N—H⋯S interactions, along with parallel π–π interactions between imidazole and benzene rings, in the second compound.


Introduction
1H-Benzimidazole-2(3H)-thione, (1) (see Scheme 1), is a planar molecule with two substitutable acidic H atoms. The N atoms of this molecule have demonstrated the ability to form Lewis acid-base coordination compounds. Under basic conditions, the corresponding salt of (1) has been shown to react with p-block elements (O'Sullivan & Wallis, 1972).

Experimental
All reagents were purchased from Aldrich and were used as received. All solvents were dried before use. 1 H NMR (300.13185 MHz) and 13 C NMR (75.47564 MHz) analyses in CDCl 3 were performed on a Bruker 300 MHz spectrometer, using TMS as the internal reference. Chemical shifts () are reported in p.p.m. IR spectra were recorded on a Perkin-Elmer FT-IR 1600 spectrophotometer in the 4000-400 cm À1 range. Elemental analyses were performed in a Thermofinniga Flash 112 instrument under standard conditions.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms were included in geometrically calculated positions, riding on the C or N atoms to which they were bonded. C-H distances were restrained to 0.93 (aromatic) or 0.96 Å (methyl) and the N-H bond length was restrained to 0.86 Å . H-atom displacement parameters were set at U iso (H) = 1.5U eq (C) for methyl H atoms and at 1.2U eq (C,N) otherwise.
Compound (   The molecular structure of compound (2), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
The molecular structures of the two independent molecules of compound (3), showing the atom-numbering schemes. Displacement ellipsoids are drawn at the 30% probability level.
Overall, compounds (2) and (3) have very similar structures, which are shown in Figs. 1 and 2, respectively. Selected bond lengths and angles are listed in Tables 2 and 3, respectively. The average C-Si bond length for both compounds is 1.847 (3) Å and the average C-Si-C angle is 109.5 (2) , in agreement with sp 3 -hybridization of the Si atoms. These values agree with those in similar structures reported previously (Wagler et al., 2010).
(a) The crystal packing diagram of (3) along the direction of the ab plane. (b) A detailed view of the formation of the R 2 2 (8) hydrogen-bonding motif and thestacking interactions. Table 2 Selected geometric parameters (Å , ) for (2).
À3.2 (4) Si2-N3-C2-S1 3.9 (5) ment of 0.007 (1) Å from the benzimidazole molecular plane, whereas in (2), the S atom is out of the plane by 0.155 (2) Å . This displacement could be caused by noncovalent intramolecular interactions between the S-atom nucleus and both Si atoms, or between the methyl H atoms and the S atom.
Comparing the structures of (2) and (3), it becomes obvious that the fused rings in (2) are not completely flat. Specifically, the thiourea unit composed of atoms N1/C2/N3/S1 is offset from the molecular plane defined by the benzene ring. This is a consequence of the intramolecular noncovalent C-HÁ Á ÁS interactions present in the system. Fig. 3(a) shows the spiral arrangement of (2), which forms a linking interaction between molecules through the imidazole ring (C10-H10AÁ Á ÁCg1 = 2.94 Å ; Cg1 is the centroid of the imidazole ring) and the benzene ring [C10-H10BÁ Á ÁCg2 = 2.83 Å ; Cg2 is the centroid of the benzene ring at (x À 1 2 , Ày + 3 2 , Àz)]. These interactions form a helicoidal repeat unit of 10.03 Å , which extends along the crystallographic a axis. Fig. 3(b) presents the helix overlap of this system. A third interaction, viz. C13-H13Á Á Á(x + 1 2 , Ày + 1 2 , Àz), has a CÁ Á Á distance of 2.77 Å , which further supports the helicoidal arrangement.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq    (1975) is used with some modification.