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

Böhme, U.; Bitto, F.

doi:10.1107/S2414314620014443

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 5| Part 11| November 2020| x201444

https://doi.org/10.1107/S2414314620014443

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

Uwe Böhme ^a ^* and Florian Bitto ^a

^aInstitut für Anorganische Chemie, Technische Universität Bergakademie Freiberg, Leipziger Str. 29, 09599 Freiberg, Germany
^*Correspondence e-mail: uwe.boehme@chemie.tu-freiberg.de

Edited by J. Simpson, University of Otago, New Zealand (Received 23 October 2020; accepted 30 October 2020; online 6 November 2020)

The title compound, C₈H₁₆N₂Si, crystallizes in the the orthorhombic space group P2₁2₁2₁ with one molecule in the asymmetric unit. The Si—N bond is 1.782 (2) Å, which 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.

Keywords: crystal structure; in situ crystallization; organosilane.

CCDC reference: 2041610

Structure description

Silanes substituted with 3,5-dimethylpyrazolyl units have been investigated over the last twenty years as an alternative to the long-known pyrazolylborates (Pullen et al., 2000 ; Kuzu et al., 2008 ; Armbruster et al. 2009 ). Such (3,5-dimethylpyrazolyl)silanes form potent multidentate ligands with a `podand topology' (Gade 2002a ,b ,c ).

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., 2012 , 2013 , 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 für 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.

The title compound crystallizes in the orthorhombic space group P2₁2₁2₁ with one molecule in the asymmetric unit (Fig. 1). The Si1—N1 bond is 1.782 (2) Å long. This is substantially longer than comparable bonds in tris(3,5-dimethylpyrazolyl)methylsilane [1.745 (5) Å; Vepachedu et al., 1995 ] and tetrakis(3,5-dimethylpyrazolyl)silane [from 1.712 (3) to 1.725 (3) Å; Armbruster et al. 2009). The pyrazol ring is planar with an r.m.s. deviation of 0.003 Å from the ring plane. The trimethylsilyl group adopts a staggered conformation with respect to the plane of the 3,5-dimethylpyrazolyl unit. This can be seen in the torsion angles C8—Si1—N1—N2 with −35.1 (2)° and C6—Si1—N1—C2 with 36.3 (2)°. The methyl group C7 is orientated perpendicular to the 3,5-dimethylpyrazolyl unit. There is a hydrogen bond between the hydrogen atom at C6 and the nitrogen atom N2 from a neighboring molecule (see Table 1). These hydrogen bonds form a strand of molecules generated by a twofold screw axis (2₁) along the crystallographic b axis (see Fig. 2).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C6—H6B⋯N2ⁱ	0.97	2.75	3.670 (3)	159
Symmetry code: (i) $[-x+2, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ .

Figure 1
The molecular structure of the title compound, drawn with 50% probability displacement ellipsoids.

Figure 2
Hydrogen bonds between N2 and H6B of neighboring molecules along a twofold screw axis (2₁) parallel to the crystallographic b axis.

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.

Table 2
Experimental details

Crystal data
Chemical formula	C₈H₁₆N₂Si
M_r	168.32
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	250
a, b, c (Å)	6.1056 (3), 10.8114 (7), 15.5867 (9)
V (Å³)	1028.88 (10)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.18
Crystal size (mm)	0.50 × 0.40 × 0.40

Data collection
Diffractometer	STOE IPDS 2
Absorption correction	Integration (X-RED; Stoe, 2009 )
T_min, T_max	0.708, 0.932
No. of measured, independent and observed [I > 2σ(I)] reflections	8249, 2346, 2258
R_int	0.048
(sin θ/λ)_max (Å⁻¹)	0.650

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.030, 0.080, 1.09
No. of reflections	2346
No. of parameters	106
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.12, −0.15
Absolute structure	Flack x determined using 896 quotients [(I⁺)−(I⁻)]/[(I⁺)+(I⁻)] (Parsons et al., 2013 )
Absolute structure parameter	0.07 (9)
Computer programs: X-AREA and X-RED (Stoe, 2009), SHELXS97 (Sheldrick, 2008 ), SHELXL2014/7 (Sheldrick 2015 ) and ORTEP-3 for Windows (Farrugia, 2012 ).

Structural data

CCDC reference: 2041610

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314620014443/sj4215sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314620014443/sj4215Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314620014443/sj4215Isup3.cml

checkCIF report

Computing details top

Data collection: X-AREA (Stoe, 2009); cell refinement: X-AREA (Stoe, 2009); data reduction: X-RED (Stoe, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014/7 (Sheldrick 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL2014/7 (Sheldrick 2015).

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

Crystal data top

C₈H₁₆N₂Si	D_x = 1.087 Mg m⁻³
M_r = 168.32	Melting point: 260 K
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
a = 6.1056 (3) Å	Cell parameters from 32385 reflections
b = 10.8114 (7) Å	θ = 2.3–29.7°
c = 15.5867 (9) Å	µ = 0.18 mm⁻¹
V = 1028.88 (10) Å³	T = 250 K
Z = 4	Capillary, colourless
F(000) = 368	0.50 × 0.40 × 0.40 mm

Data collection top

STOE IPDS 2 diffractometer	2346 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	2258 reflections with I > 2σ(I)
Plane graphite monochromator	R_int = 0.048
Detector resolution: 6.67 pixels mm^-1	θ_max = 27.5°, θ_min = 2.3°
rotation method scans	h = −7→6
Absorption correction: integration (X-RED; Stoe, 2009)	k = −14→14
T_min = 0.708, T_max = 0.932	l = −19→20
8249 measured reflections

Refinement top

Refinement on F²	H-atom parameters constrained
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0384P)² + 0.1226P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.030	(Δ/σ)_max < 0.001
wR(F²) = 0.080	Δρ_max = 0.12 e Å⁻³
S = 1.09	Δρ_min = −0.15 e Å⁻³
2346 reflections	Extinction correction: SHELXL-2014/7 (Sheldrick 2015, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
106 parameters	Extinction coefficient: 0.038 (8)
0 restraints	Absolute structure: Flack x determined using 896 quotients [(I⁺)-(I^-)]/[(I⁺)+(I^-)] (Parsons et al., 2013)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.07 (9)
Hydrogen site location: inferred from neighbouring sites

Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Si1	1.09038 (8)	0.83129 (5)	0.28856 (3)	0.03560 (16)
N1	0.9829 (3)	0.91025 (15)	0.37963 (9)	0.0371 (3)
N2	0.8044 (3)	0.98582 (17)	0.36345 (11)	0.0449 (4)
C1	1.2467 (4)	0.8620 (3)	0.49915 (16)	0.0604 (6)
H1A	1.2704	0.8905	0.5574	0.091*
H1B	1.3765	0.8782	0.4651	0.091*
H1C	1.2171	0.7738	0.4996	0.091*
C2	1.0558 (3)	0.92883 (18)	0.46120 (11)	0.0390 (4)
C3	0.9227 (4)	1.01575 (19)	0.49782 (12)	0.0443 (4)
H3	0.9317	1.0469	0.5540	0.053*
C4	0.7709 (4)	1.04880 (18)	0.43507 (13)	0.0422 (4)
C5	0.5894 (5)	1.1411 (2)	0.44085 (18)	0.0670 (7)
H5A	0.6504	1.2230	0.4493	0.100*
H5B	0.4951	1.1204	0.4888	0.100*
H5C	0.5049	1.1397	0.3882	0.100*
C6	1.2361 (4)	0.6905 (2)	0.32373 (15)	0.0544 (6)
H6A	1.3721	0.7136	0.3516	0.082*
H6B	1.2677	0.6390	0.2743	0.082*
H6C	1.1450	0.6449	0.3637	0.082*
C7	1.2781 (5)	0.9387 (2)	0.23290 (16)	0.0593 (6)
H7A	1.1987	1.0127	0.2163	0.089*
H7B	1.3368	0.8989	0.1821	0.089*
H7C	1.3972	0.9610	0.2711	0.089*
C8	0.8569 (4)	0.7920 (3)	0.21896 (16)	0.0589 (6)
H8A	0.7518	0.7433	0.2511	0.088*
H8B	0.9084	0.7447	0.1701	0.088*
H8C	0.7875	0.8675	0.1990	0.088*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Si1	0.0353 (2)	0.0376 (3)	0.0339 (2)	0.0038 (2)	0.0023 (2)	0.00083 (19)
N1	0.0377 (8)	0.0398 (8)	0.0338 (7)	0.0062 (7)	0.0010 (6)	0.0016 (6)
N2	0.0477 (10)	0.0474 (9)	0.0395 (8)	0.0141 (8)	−0.0014 (7)	0.0014 (7)
C1	0.0550 (13)	0.0720 (16)	0.0541 (13)	0.0143 (12)	−0.0176 (10)	−0.0073 (11)
C2	0.0396 (10)	0.0414 (9)	0.0361 (8)	−0.0028 (8)	−0.0016 (8)	0.0000 (7)
C3	0.0515 (11)	0.0435 (10)	0.0380 (8)	−0.0020 (10)	0.0016 (9)	−0.0049 (8)
C4	0.0452 (11)	0.0375 (10)	0.0438 (10)	0.0042 (8)	0.0072 (8)	−0.0007 (7)
C5	0.0701 (16)	0.0590 (14)	0.0718 (16)	0.0264 (14)	0.0064 (14)	−0.0074 (11)
C6	0.0651 (14)	0.0476 (12)	0.0506 (12)	0.0175 (11)	0.0024 (11)	0.0007 (9)
C7	0.0599 (14)	0.0557 (13)	0.0623 (14)	−0.0014 (12)	0.0219 (12)	0.0060 (10)
C8	0.0500 (12)	0.0713 (15)	0.0554 (13)	0.0044 (11)	−0.0075 (10)	−0.0176 (12)

Geometric parameters (Å, º) top

Si1—N1	1.7816 (15)	C4—C5	1.494 (3)
Si1—C8	1.841 (2)	C5—H5A	0.9700
Si1—C6	1.847 (2)	C5—H5B	0.9700
Si1—C7	1.848 (2)	C5—H5C	0.9700
N1—C2	1.362 (2)	C6—H6A	0.9700
N1—N2	1.385 (2)	C6—H6B	0.9700
N2—C4	1.324 (3)	C6—H6C	0.9700
C1—C2	1.494 (3)	C7—H7A	0.9700
C1—H1A	0.9700	C7—H7B	0.9700
C1—H1B	0.9700	C7—H7C	0.9700
C1—H1C	0.9700	C8—H8A	0.9700
C2—C3	1.367 (3)	C8—H8B	0.9700
C3—C4	1.394 (3)	C8—H8C	0.9700
C3—H3	0.9400

N1—Si1—C8	107.15 (10)	C4—C5—H5A	109.5
N1—Si1—C6	109.63 (9)	C4—C5—H5B	109.5
C8—Si1—C6	110.98 (13)	H5A—C5—H5B	109.5
N1—Si1—C7	107.53 (10)	C4—C5—H5C	109.5
C8—Si1—C7	110.39 (13)	H5A—C5—H5C	109.5
C6—Si1—C7	111.02 (13)	H5B—C5—H5C	109.5
C2—N1—N2	109.87 (15)	Si1—C6—H6A	109.5
C2—N1—Si1	133.98 (14)	Si1—C6—H6B	109.5
N2—N1—Si1	115.29 (11)	H6A—C6—H6B	109.5
C4—N2—N1	105.74 (16)	Si1—C6—H6C	109.5
C2—C1—H1A	109.5	H6A—C6—H6C	109.5
C2—C1—H1B	109.5	H6B—C6—H6C	109.5
H1A—C1—H1B	109.5	Si1—C7—H7A	109.5
C2—C1—H1C	109.5	Si1—C7—H7B	109.5
H1A—C1—H1C	109.5	H7A—C7—H7B	109.5
H1B—C1—H1C	109.5	Si1—C7—H7C	109.5
N1—C2—C3	107.29 (18)	H7A—C7—H7C	109.5
N1—C2—C1	123.58 (18)	H7B—C7—H7C	109.5
C3—C2—C1	129.12 (19)	Si1—C8—H8A	109.5
C2—C3—C4	106.16 (17)	Si1—C8—H8B	109.5
C2—C3—H3	126.9	H8A—C8—H8B	109.5
C4—C3—H3	126.9	Si1—C8—H8C	109.5
N2—C4—C3	110.94 (18)	H8A—C8—H8C	109.5
N2—C4—C5	120.6 (2)	H8B—C8—H8C	109.5
C3—C4—C5	128.5 (2)

C8—Si1—N1—C2	156.8 (2)	Si1—N1—C2—C3	169.00 (16)
C6—Si1—N1—C2	36.3 (2)	N2—N1—C2—C1	−179.88 (19)
C7—Si1—N1—C2	−84.5 (2)	Si1—N1—C2—C1	−11.4 (3)
C8—Si1—N1—N2	−35.13 (18)	N1—C2—C3—C4	−0.7 (2)
C6—Si1—N1—N2	−155.65 (15)	C1—C2—C3—C4	179.8 (2)
C7—Si1—N1—N2	83.55 (17)	N1—N2—C4—C3	−0.3 (2)
C2—N1—N2—C4	−0.1 (2)	N1—N2—C4—C5	179.69 (19)
Si1—N1—N2—C4	−171.00 (14)	C2—C3—C4—N2	0.6 (3)
N2—N1—C2—C3	0.5 (2)	C2—C3—C4—C5	−179.4 (2)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C6—H6B···N2ⁱ	0.97	2.75	3.670 (3)	159

Symmetry code: (i) −x+2, y−1/2, −z+1/2.

Funding information

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

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