Crystal structure of trans-1,4-bis­[(tri­methyl­sil­yl)­oxy]cyclo­hexa-2,5-diene-1,4-dicarbo­nitrile

The mol­ecular structure of the title compound is centrosymmetric. The cyclo­hexa-2,5-diene moiety is exactly planar and has a bond-length distribution characteristic for one pair of double bonds and two pairs of single bonds.

Abstract

The asymmetric unit of the title compound, C₁₄H₂₂N₂O₂Si₂, contains one half of the mol­ecule, which is completed by inversion symmetry. The cyclo­hexa-2,5-diene ring is exactly planar and reflects the bond-length distribution of a pair of located double bonds [1.3224 (14) Å] and two pairs of single bonds [1.5121 (13) and 1.5073 (14) Å]. The tetra­hedral angle between the sp ³-C atom and the two neighbouring sp ²-C atoms in the cyclo­hexa-2,5-diene ring is enlarged by about 3°.

Chemical context  

Cyano­hydrins (Friedrich, 1983 ▶) are an important class of organic compounds. Silylated cyano­hydrins are versatile precursor compounds in organic chemistry because the nitrile functional group can be modified by a variety of reactions such as hydrolysis, reduction or addition of organometallic reagents. The mol­ecular and crystal structure of the title compound, a new silylated cyclo­hexa-2,5-diene with trans nitrile groups in the 1,4 positions, is reported herein.

Structural commentary  

The mol­ecular structure of the title compound is centrosymmetric, leading to a trans-1,4-configuration of the oxy(tri­methyl­sil­yl) and carbo­nitrile groups (Fig. 1 ▶). The cyclo­hexa-2,5-diene ring is exactly planar, but its angles differ from that of an ideal hexa­gon. Whereas the angle between the sp ³-C atom (C1) and the neighbouring sp ²-C atoms (C2, C3) is reduced to 112.58 (8)°, the other intra-ring angles are enlarged to 123.94 (9)° (C1—C2—C3) and 123.48 (9)° (C1ⁱ—C3—C2) [symmetry code: (i) −x + 1, −y + 1, −z]. The tetra­hedral angles around C1 are likewise distorted due to the ring strain. The angles involving the O atom of the oxy(tri­methyl­sil­yl) group and the ring C atoms are enlarged to 110.79 (8)° and 113.26 (8)° while the angle involving the O atom and the C atom of the carbo­nitrile group is reduced to 104.95 (8)°. The backbone of the 1,1-substituents is nearly perpendicular to the cyclo­hexa-2,5-diene ring, with a dihedral angle of 86.05 (7).

Figure 1.

The mol­ecular structure of the title compound, showing the atom-labelling scheme and displacement ellipsoids drawn at the 80% probability level. Non-labelled atoms are generated by the symmetry code −x + 1, −y + 1, −z.

Supra­molecular features  

Notable features in terms of non-classical hydrogen bonding inter­actions are not observed in the crystal structure of the title compound. As a result of the bulky tri­methyl­silyl groups, π–π stacking inter­actions between the rings are not possible. The packing of the mol­ecules (Fig. 2 ▶) seems to be dominated mainly by van der Waals forces.

Figure 2.

A view of the crystal packing of the title compound along [001]. Colour code: O red, C grey, N light-blue, Si off-white, H white.

Database survey  

In the current Cambridge Structural Database (Version 5.35, last update February 2014; Allen, 2002 ▶) only one example of a cyclo­hexa-2,5-diene with trans nitrile groups in the 1,4 positions is listed, namely 3,5-bis­(4-(di­methyl­amino)­phen­yl)cyclo­hexa-2,5-diene-1,1,2,4,4-penta­carbo­nitrile (Jayamurugan et al., 2011 ▶). The C—C bond lengths within the cyclo­hexa-2,5-diene are very similar to those of the title compound.

Synthesis and crystallization  

1,4-Bis[(tri­methyl­sil­yl)­oxy]cyclo­hexa-2,5-diene-1,4-dicarbonitrile was synthesized by a modified protocol reported by Onaka et al. (1989 ▶). The required heterogeneous catalyst Fe-montmorillonite (K10-FeAA) was prepared according to Pai et al. (2000 ▶) and activated at 393 K and 5 mbar for 2 h prior to use.

1,4-Benzo­quinone (1.62 g, 15 mmol) was dissolved in 75 ml di­chloro­methane (0.2 M), purged with argon and cooled to 273 K. Tri­methyl­silyl cyanide (2.98 g, 30 mmol) and Fe-montmorillonite (0.75 g) were added sequentially and the mixture stirred for 1 h at 273 K under an argon atmosphere. The Fe-montmorillonite was filtered off (Por 4 glass filter) and the solvent was evaporated in vacuo to yield 4.23 g (13.8 mmol, 92%) of a cis/trans (3/1) isomeric mixture of 1,4-bis­[(tri­methyl­sil­yl)­oxy]cyclo­hexa-2,5-diene-1,4-dicarbo­nitrile (Fig. 3 ▶). Crystallization from n-hexane selectively yielded white crystals of the trans-isomer, which were suitable for single-crystal X-ray diffraction analysis. ¹H NMR (CDCl₃, 200 MHz): δ = 6.19 (s, 4H), 0.23 (s, 18H) p.p.m.; ¹³C NMR (CDCl₃, 50 MHz): δ = 238.3 (s), 129.4 (d), 1.5 (q) p.p.m.

Figure 3.

Reaction scheme to obtain the title compound.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 1 ▶. The H atoms were included in calculated positions (C—H = 0.96 Å) and treated as riding atoms with U _iso(H) = 1.2U _eq(C).

Table 1. Experimental details.

Crystal data
Chemical formula	C14H22N2O2Si2
M r	306.5
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	100
a, b, c (Å)	8.0770 (5), 11.2234 (6), 9.4377 (6)
β (°)	97.7087 (19)
V (Å3)	847.81 (9)
Z	2
Radiation type	Mo Kα
μ (mm−1)	0.21
Crystal size (mm)	0.65 × 0.26 × 0.12
Data collection
Diffractometer	Bruker Kappa APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2013 ▶)
T min, T max	0.94, 0.98
No. of measured, independent and observed [I > 3σ(I)] reflections	15160, 2487, 2123
R int	0.024
(sin θ/λ)max (Å−1)	0.705
Refinement
R[F 2 > 3σ(F 2)], wR(F 2), S	0.030, 0.042, 2.38
No. of reflections	2487
No. of parameters	91
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.38, −0.20

Computer programs: APEX2 and SAINT-Plus (Bruker, 2013 ▶), SUPERFLIP (Palatinus & Chapuis, 2007 ▶), JANA2006 (Petříček, et al., 2014 ▶), Mercury (Macrae et al., 2008 ▶) and publCIF (Westrip, 2010 ▶).

Supplementary Material

CCDC reference: 1008752

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

C14H22N2O2Si2	F(000) = 328
Mr = 306.5	Dx = 1.200 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 7267 reflections
a = 8.0770 (5) Å	θ = 2.8–29.9°
b = 11.2234 (6) Å	µ = 0.21 mm−1
c = 9.4377 (6) Å	T = 100 K
β = 97.7087 (19)°	Block, clear colourless
V = 847.81 (9) Å3	0.65 × 0.26 × 0.12 mm
Z = 2

Data collection

Bruker Kappa APEXII CCD diffractometer	2487 independent reflections
Radiation source: X-ray tube	2123 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.024
ω and φ–scans	θmax = 30.1°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Bruker, 2013)	h = −11→11
Tmin = 0.94, Tmax = 0.98	k = −15→15
15160 measured reflections	l = −13→13

Refinement

Refinement on F	44 constraints
R[F2 > 2σ(F2)] = 0.030	H-atom parameters constrained
wR(F2) = 0.042	Weighting scheme based on measured s.u.'s w = 1/(σ2(F) + 0.0001F2)
S = 2.38	(Δ/σ)max = 0.023
2487 reflections	Δρmax = 0.38 e Å−3
91 parameters	Δρmin = −0.20 e Å−3
0 restraints

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Si1	0.21973 (4)	0.48658 (3)	0.25729 (3)	0.01515 (9)
O1	0.34897 (9)	0.59176 (6)	0.20989 (8)	0.0151 (2)
N1	0.66734 (12)	0.77227 (8)	0.18067 (10)	0.0203 (3)
C1	0.47262 (12)	0.58514 (9)	0.11702 (10)	0.0118 (3)
C2	0.39530 (12)	0.59953 (9)	−0.03704 (10)	0.0130 (3)
C3	0.41937 (12)	0.52449 (9)	−0.14034 (11)	0.0125 (3)
C4	0.58275 (13)	0.69117 (9)	0.15441 (10)	0.0136 (3)
C5	0.04800 (15)	0.57505 (11)	0.31580 (13)	0.0244 (4)
C6	0.32433 (16)	0.39773 (11)	0.40911 (13)	0.0303 (4)
C7	0.14743 (14)	0.38628 (10)	0.10522 (12)	0.0208 (3)
H1c2	0.324479	0.667221	−0.061301	0.0155*
H1c3	0.365173	0.540694	−0.235238	0.015*
H1c5	−0.036613	0.522349	0.341718	0.0293*
H2c5	0.09082	0.622785	0.396915	0.0293*
H3c5	0.000656	0.625942	0.239152	0.0293*
H1c6	0.246714	0.341141	0.438738	0.0363*
H2c6	0.417964	0.356223	0.379805	0.0363*
H3c6	0.362472	0.449816	0.487404	0.0363*
H1c7	0.049234	0.344384	0.124438	0.0249*
H2c7	0.121741	0.432548	0.019545	0.0249*
H3c7	0.233911	0.330007	0.093019	0.0249*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Si1	0.01621 (16)	0.01632 (17)	0.01325 (15)	−0.00379 (11)	0.00316 (11)	−0.00069 (11)
O1	0.0166 (4)	0.0138 (4)	0.0161 (4)	−0.0014 (3)	0.0071 (3)	−0.0023 (3)
N1	0.0220 (5)	0.0178 (5)	0.0210 (5)	−0.0034 (4)	0.0026 (4)	−0.0036 (4)
C1	0.0132 (4)	0.0106 (5)	0.0118 (4)	−0.0006 (3)	0.0026 (3)	−0.0006 (3)
C2	0.0126 (4)	0.0112 (5)	0.0147 (5)	0.0009 (4)	0.0001 (4)	0.0016 (4)
C3	0.0126 (5)	0.0121 (5)	0.0122 (4)	0.0000 (4)	−0.0005 (4)	0.0017 (4)
C4	0.0151 (5)	0.0143 (5)	0.0115 (4)	0.0018 (4)	0.0021 (3)	−0.0004 (4)
C5	0.0226 (6)	0.0291 (7)	0.0236 (6)	−0.0046 (5)	0.0102 (5)	−0.0070 (5)
C6	0.0327 (7)	0.0314 (7)	0.0249 (6)	−0.0108 (5)	−0.0029 (5)	0.0105 (5)
C7	0.0215 (6)	0.0219 (6)	0.0198 (5)	−0.0064 (4)	0.0058 (4)	−0.0038 (4)

Geometric parameters (Å, º)

Si1—C5	1.8495 (13)	C3—H1c3	0.96
Si1—C6	1.8537 (13)	C5—H1c5	0.96
Si1—C7	1.8555 (11)	C5—H2c5	0.96
O1—C1	1.4163 (13)	C5—H3c5	0.96
N1—C4	1.1451 (14)	C6—H1c6	0.96
C1—C2	1.5121 (13)	C6—H2c6	0.96
C1—C3i	1.5073 (14)	C6—H3c6	0.96
C1—C4	1.4993 (14)	C7—H1c7	0.96
C2—C3	1.3224 (14)	C7—H2c7	0.96
C2—H1c2	0.96	C7—H3c7	0.96
C5—Si1—C6	109.89 (6)	Si1—C5—H2c5	109.47
C5—Si1—C7	112.70 (5)	Si1—C5—H3c5	109.47
C6—Si1—C7	109.57 (5)	H1c5—C5—H2c5	109.47
O1—C1—C2	110.79 (8)	H1c5—C5—H3c5	109.47
O1—C1—C3i	113.26 (8)	H2c5—C5—H3c5	109.47
O1—C1—C4	104.95 (8)	Si1—C6—H1c6	109.47
C2—C1—C3i	112.58 (8)	Si1—C6—H2c6	109.47
C2—C1—C4	107.28 (8)	Si1—C6—H3c6	109.47
C3i—C1—C4	107.46 (8)	H1c6—C6—H2c6	109.47
C1—C2—C3	123.94 (9)	H1c6—C6—H3c6	109.47
C1—C2—H1c2	118.03	H2c6—C6—H3c6	109.47
C3—C2—H1c2	118.03	Si1—C7—H1c7	109.47
C1i—C3—C2	123.48 (9)	Si1—C7—H2c7	109.47
C1i—C3—H1c3	118.26	Si1—C7—H3c7	109.47
C2—C3—H1c3	118.26	H1c7—C7—H2c7	109.47
N1—C4—C1	178.87 (11)	H1c7—C7—H3c7	109.47
Si1—C5—H1c5	109.47	H2c7—C7—H3c7	109.47

Symmetry code: (i) −x+1, −y+1, −z.