Crystal structure of 3-methyl-5-trimethylsilyl-1H-pyrazole

The title compound, C7H14N2Si, crystallizes in a tetragonal space group and exists as an N—H⋯N hydrogen-bonded tetramer, formed around the crystallographic fourfold rotoinversion axis. The molecular identity is clearly the 5-trimethylsilyl-3-methyl-1H-pyrazole tautomer and the structure is isomorphous with that of 5-tert-butyl-3-methyl-1H-pyrazole [Foces-Foces & Trofimenko (2001 ▸). Acta Cryst. E57, o32–o34].

salts. The trispyrazolylborates make excellent supporting ligands for stabilization of a wide range of metal-organic coordination compounds. Most often functioning as tridentate ligands, this class of molecules is often referred to as the scorpionates (Trofimenko, 1999). We have studied a variety of tris(3-tert-butyl-5-methyl)pyrazolylborate supported metal complexes and have found the 27 proton tert-butyl resonance in the 1 H NMR to often obscure important resonances from other aliphatic fragments. Replacing the tert-butyl group with a trimethylsilyl group would clear the standard aliphatic region of the NMR spectrum. During the course of our studies, we obtained X-ray quality crystals of the title compound which is reported herein.

S4. Database survey
Pyrazoles are ubiquitous, particularly as building blocks for pyrazolylborate metal complexes.

S5. Synthesis and crystallization
Synthesis of the title compound was accomplished following a literature procedure involving reaction of trimethylsilyldiazomethane with n-butyllithium, followed by reaction with the α, β-unsaturated methacrylonitrile (Aoyama et al., 1984). X-ray quality crystals were obtained by slow evaporation of a chloroform solution of the title compound.

S6. Refinement
The pyrazole-H atom was located in a difference Fourier map and refined freely. All other H atoms were initially located in a difference Fourier map, but were included in the final refinement using the standard geometrically idealized positions and refined using the riding-model approximation (C-H = 0.95 and 0.98 Å for Ar-H and CH 3 ; U iso (H) = 1.2U eq (C) for the aromatic H atom and U iso (H) = 1.5U eq (C)) for methyl groups. The H atoms of the C6-methyl group were refined as orientationally disordered using the AFIX 127 command in SHELX2014 (Sheldrick, 2015), with refined occupancies of 0.58 (3) and 0.42 (3) for the two moieties, respectively.
Crystal data, data collection and structure refinement details are summarized in Table 1. Mercury rendering of the R 4 4 (12) H-bonding motif view of the title compound. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.38 e Å −3 Δρ min = −0.28 e Å −3 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.