(3,5-Dimethyl-1H-pyrazol-1-yl)trimethylsilane

At 1.782 (2) Å, the Si—N bond is substantially longer than is found in comparable (3,5-dimethylpyrazolyl)silanes. The trimethylsilyl group adopts a staggered conformation with respect to the planar 3,5-dimethylpyrazolyl unit. C—H⋯N hydrogen bonds between neighboring molecules form a strand of molecules along the b-axis direction.

The title compound (3,5-dimethyl-1H-pyrazol-1-yl)trimethylsilane is a key compound in the preparation of different (3,5-dimethylpyrazolyl)silanes by transsilylation (Armbruster et al., 2009;Bitto et al., 2012Bitto et al., , 2013Bitto et al., , 2016a. The solid-state structure of this compound has never been determined, since it is a liquid at room temperature. In situ cryo-crystallization of low-melting compounds has been practiced for many years (Atoji et al., 1955;Smith & Lipscomb, 1965;Brodalla et al., 1985). Different in situ cryo-crystallization techniques have been described in a review (Boese & Nussbaumer, 1994). State of the art of in situ crystallization is summarized recently in a special issue of Zeitschrift fü r Kristallographie (Boese, 2014). We have performed several single-crystal structure determinations of pyrophoric liquids by in situ crystallization on the diffractometer (Schmidt et al., 2013;Gerwig et al. 2020). With the experience gained in these processes, we were able to crystallize the title compound on the diffractometer and we report its crystal structure here.

Synthesis and crystallization
The title compound was prepared from 3,5-dimethylpyrazol (19.23 g, 0.2 mol) and chlorotrimethylsilane (22.81 g, 0.21 mol). The reaction was performed in 300 ml THF as solvent and in the presence of triethylamine (21.25 g, 0.21 mol). Triethylamine hydrochloride is formed during the reaction as a voluminous white precipitate. This precipitate is filtered off. After that the solvent is distilled off in vacuo. The title compound is isolated by vacuum distillation at 107 C and 1.3 kPa. It is a colourless liquid (26.97 g, 0.16 mol, 80% yield) (Bitto 2016b).
The compound was filled as liquid with 10% n-pentane in a glass capillary with 0.5 mm diameter. A single crystal was grown on the diffractometer at 255 K. The data collection was perfomed at a slightly lower temperature in order to have a stable crystal on the diffractometer.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

Funding information
Funding for this research was provided by: Open Access Funding by the Publication Fund of the TU Bergakademie Freiberg.

data-1
IUCrData ( Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.