Analysis of the molecular structure of chloromethyltri(thiophen-2-yl)silane

Abstract

Heteroatoms in the -position relative to a silicon atom can prove to have a specific effect on the structure and the overall properties of silicon derivatives through a so called -effect. This continues to attract the attention of investigators [1]. We have previously discovered the structural manifestation of this -effect in the case of furylsilyl derivatives [2, 3]. Hence the monoand di(furan-2-yl)silyl silicon compounds showed a marked decrease in the Si–C–O angle when compared with the Si–C–C angle. For example, in the model compounds of silatrane 1-sila2,8,9-trioxa-5-azabicyclo[3.3.3]undecane − 1-(furan-2-yl)silatrane and 1-{2-[dimethyl(furan-2-yl)silyl]ethyl}silatrane this difference reaches 16o. In the case of di(furan-2-yl)silane the difference in angles for the first and second furyl groups are 15o and 12o. For the two of the furyl groups in tri(2-furyl)silane, the differences in the above noted angles are also 15o and 12o but the appearance of the -effect for the third furyl group is minimal, the difference in angles being only 4.2o. The absence of a heteroatom in the -position relative to the silicon atom in 1-(furan-3-yl)silatrane leads to almost complete equivalence of the Si–C–C angles, the difference between them being only 1o. It was therefore of interest to study the steric structure of 2-thienyl silicon derivatives containing a sulfur atom in the -position relative to the silicon atom. X-ray analysis of the single crystal of chloromethyltri(thiopen-2-yl)silane was carried out with the aim of establishing the molecular and crystal structures (Figure 1). It was found that the bond length for Si(1)–C(1) was 1.874(5) A and somewhat shorter for the Si–C(sp) bonds: viz. Si(1)–C(2A) 1.869(5), Si(1)–C(2B) 1.860(5), and Si(1)–C(2C) 1.854(5) A. It should be noted that the angles Si–C–S and Si–C–C for the thienyl groups in the molecule differ insignificantly and this points to the absence of a marked -effect on the molecular geometry. A statical disordering is observed in the crystal structure. Primarily in the crystal, molecules (80%) are present with a torsion angle  of -46.6(2)o for C(1)–Si(1)–C(2C)–S(1C) but also molecules (20%) with another conformation in which the torsional angle C(1)–Si(1)–C(2C)–S(1C') differs from the value of  by 180o. Such disordering is characteristic for crystal structures with 2-thienyl substituents [4]. Molecular packing occurs at distances not less than the sum of the van der Waal radii of the contacting atoms. The chloromethyltri(thiophen-2-yl)silane was prepared by the known method [5].