1,1,3,3-Tetra-tert-butyl-2,2-diisopropyl-4,4-diphenyl­cyclo­tetra­silane

Takayoshi Kuribara; Soichiro Kyushin

doi:10.1107/S160053681205074X

. 2012 Dec 22;69(Pt 1):o149. doi: 10.1107/S160053681205074X

1,1,3,3-Tetra-tert-butyl-2,2-diisopropyl-4,4-diphenylcyclotetrasilane

Takayoshi Kuribara ^a, Soichiro Kyushin ^a,^*

PMCID: PMC3588281 PMID: 23476402

Abstract

The molecule in the structure of the title compound, C₃₄H₆₀Si₄, lies on a twofold rotation axis that passes through the two Si atoms, resulting in a planar cyclotetrasilane ring. The dihedral angle between the cyclotetrasilane ring and the phenyl ring is 68.20 (5)°. The Si—Si bonds [2.4404 (8) and 2.4576 (8) Å] are longer than a standard Si—Si bond (2.34 Å) and the C—Si—C bond angle [97.07 (14)°] of the phenyl-substituted Si atom is smaller than the tetrahedral bond angle (109.5°). These long bonds and small bond angle are favorable for reducing the steric hindrance among the bulky substituents.

Related literature

For background to and applications of phenyl-substituted oligosilanes, see: Hinch & Krc (1957 ▶); Matsumoto & Tanaka (2008 ▶). For a related structure of a cyclotetrasilane without phenyl groups, see: Kyushin et al. (1995 ▶).

Experimental

Crystal data

C₃₄H₆₀Si₄
M _r = 581.18
Monoclinic,
a = 11.9477 (9) Å
b = 17.6585 (12) Å
c = 17.0422 (13) Å
β = 104.9394 (8)°
V = 3474.0 (4) Å³
Z = 4
Mo Kα radiation
μ = 0.19 mm⁻¹
T = 173 K
0.50 × 0.40 × 0.20 mm

Data collection

Rigaku R-AXIS IV imaging plate diffractometer
Absorption correction: multi-scan (REQAB; Jacobson, 1998 ▶) T _min = 0.910, T _max = 0.963
8534 measured reflections
2917 independent reflections
2899 reflections with I > 2σ(I)
R _int = 0.025

Refinement

R[F ² > 2σ(F ²)] = 0.048
wR(F ²) = 0.095
S = 1.24
2917 reflections
181 parameters
H-atom parameters constrained
Δρ_max = 0.24 e Å⁻³
Δρ_min = −0.20 e Å⁻³

Data collection: CrystalClear (Rigaku, 2003 ▶); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SIR2004 (Burla et al., 2005 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 2012 ▶); software used to prepare material for publication: SHELXL97 and Yadokari-XG 2009 (Kabuto et al., 2009 ▶).

Supplementary Material

Click here for additional data file.^{(27.4KB, cif)}

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S160053681205074X/is5224sup1.cif

e-69-0o149-sup1.cif^{(27.4KB, cif)}

Click here for additional data file.^{(143.3KB, hkl)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S160053681205074X/is5224Isup2.hkl

e-69-0o149-Isup2.hkl^{(143.3KB, hkl)}

Click here for additional data file.^{(11.3KB, cml)}

Supplementary material file. DOI: 10.1107/S160053681205074X/is5224Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and the Japan Society for the Promotion of Science. This work was also supported by the Element Innovation Project of Gunma University.

supplementary crystallographic information

Comment

Birefringent materials have a wide range of optical applications. Single crystals of calcium carbonate and barium borate have been well known as inorganic birefringent materials. Organic single crystals such as urea have also been known to show birefringence. Since birefringence is related to crystal structures, studies on molecular structures and packing in a crystal are important. In 1957, birefringence of tetrakis(4-phenylphenyl)silane was reported (Hinch & Krc, 1957). Recently, birefringence of single crystals of phenyl-substituted linear oligosilanes and their application to polarizers have been reported (Matsumoto & Tanaka, 2008). From these results, crystals of phenyl-substituted silicon compounds seem interesting as potential optical materials. We report herein the synthesis and X-ray crystal analysis of a phenyl-substituted cyclotetrasilane.

The coupling of 1,3-dibromo-1,1,3,3-tetra-tert-butyl-2,2-diphenyltrisilane and dichlorodiisopropylsilane with lithium in tetrahydrofuran (THF) gave 1,1,3,3-tetra-tert-butyl-2,2-diisopropyl-4,4-diphenylcyclotetrasilane (1) in 21% yield (Fig. 1). The molecular structure of 1 is shown in Fig. 2. Compound 1 has the crystallographic C2 symmetry, and therefore the cyclotetrasilane ring has a completely planar structure. The silicon–silicon bonds [2.4404 (8) and 2.4576 (8) Å] are longer than the standard silicon–silicon bond (2.34 Å). The C1—Si1—C1ⁱ bond angle [97.07 (14)°] is smaller than the tetrahedral bond angle (109.5°), while the C7—Si2—C11 [111.39 (10)°] and C15—Si3—C15ⁱ [106.97 (15)°] bond angles are within normal values. The long silicon–silicon bonds and the small carbon–silicon–carbon bond angle are favorable for reducing the steric hindrance among bulky substituents.

Packing diagram of 1 is shown in Fig. 3. Four molecules are present in a unit cell. All cyclotetrasilane rings are oriented toward the same direction with the line through the Si1 and Si3 atoms parallel to the b axis. There is no intermolecular π–π interaction among phenyl groups.

Experimental

A mixture of 1,3-dibromo-1,1,3,3-tetra-tert-butyl-2,2-diphenyltrisilane (5.00 g, 7.98 mmol), dichlorodiisopropylsilane (2.24 g, 12.1 mmol) and lithium (0.28 g, 40 mmol) in THF (50 ml) was stirred at room temperature for 1 day. The solvent was removed under reduced pressure. The residue was dissolved in hexane and passed through a short column of silica gel. After the silica gel was washed with hexane, the eluent was changed to diethyl ether. The diethyl ether eluate was evaporated. Recrystallization of the residue from methanol–THF (ca 1:1) gave 1 (0.956 g, 21%) as colorless crystals. Single crystals were obtained from methanol–THF (ca 1:1) by slow evaporation.

M.p.: 210–211 °C. ¹H NMR (400 MHz, CDCl₃): δ 1.21 (s, 36H), 1.46 (d, 12H, J = 7.4 Hz), 1.94 (sept, 2H, J = 7.4 Hz), 7.14–7.18 (m, 6H), 7.68–7.70 (m, 4H). ¹³C NMR (76 MHz, CDCl₃): δ 17.5, 24.7, 25.4, 32.8, 127.1, 127.4, 138.6, 142.1. ²⁹Si NMR (119 MHz, CDCl₃): δ -6.2, 14.0, 20.4. IR (KBr): 3050, 2950, 2920, 2850, 1470, 1420, 1390, 1360, 810, 730, 700 cm^-1. MS (EI, 70 eV): m/z 580 (M⁺, 17), 360 (100).