9,9-Dimethyl-9-silafluorene

Jan Mewes; Hans-Wolfram Lerner; Michael Bolte

doi:10.1107/S1600536809003614

. 2009 Feb 4;65(Pt 3):o451. doi: 10.1107/S1600536809003614

9,9-Dimethyl-9-silafluorene

Jan Mewes ^a, Hans-Wolfram Lerner ^a, Michael Bolte ^a,^*

PMCID: PMC2968660 PMID: 21582124

Abstract

The title compound, C₁₄H₁₄Si, crystallizes with two almost identical molecules (r.m.s. deviation = 0.080 Å for all non-H atoms) in the asymmetric unit. All atoms of the silafluorene moiety lie in a common plane (r.m.s. deviations = 0.049 and 0.035 Å for the two molecules in the asymmetric unit). The Si—C_methyl bonds are significantly shorter [1.865 (4)–1.868 (4) Å] than the Si—C_aromatic bonds [1.882 (3)–1.892 (3) Å]. Owing to strain in the five-membered ring, the endocyclic C—Si—C angles are reduced to 91.05 (14) and 91.21 (14)°.

Related literature

For the synthesis, see: Hudrlik et al. (2006 ▶). For related compounds, see: Kaufmann et al. (2008 ▶).

Experimental

Crystal data

C₁₄H₁₄Si
M _r = 210.34
Monoclinic,
a = 16.1336 (8) Å
b = 8.7752 (5) Å
c = 17.0227 (11) Å
β = 92.208 (5)°
V = 2408.2 (2) Å³
Z = 8
Mo Kα radiation
μ = 0.16 mm⁻¹
T = 173 (2) K
0.22 × 0.17 × 0.09 mm

Data collection

Stoe IPDS-II two-circle diffractometer
Absorption correction: multi-scan (MULABS; Spek, 2003 ▶; Blessing, 1995 ▶) T _min = 0.966, T _max = 0.976
38382 measured reflections
4404 independent reflections
3274 reflections with I > 2σ(I)
R _int = 0.082

Refinement

R[F ² > 2σ(F ²)] = 0.061
wR(F ²) = 0.157
S = 1.12
4404 reflections
271 parameters
H-atom parameters constrained
Δρ_max = 0.38 e Å⁻³
Δρ_min = −0.29 e Å⁻³

Data collection: X-AREA (Stoe & Cie, 2001 ▶); cell refinement: X-AREA; data reduction: X-AREA; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 2008 ▶); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2003 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536809003614/at2718sup1.cif

e-65-0o451-sup1.cif^{(23.2KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809003614/at2718Isup2.hkl

e-65-0o451-Isup2.hkl^{(215.8KB, hkl)}

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

supplementary crystallographic information

Comment

Our group has a long-standing interest in redox-switchable Lewis acids derived from ferrocenylboranes. Very recently we have synthesized 9-ferrocenyl-9-borafluorene derivatives (Kaufmann et al., 2008). Herein we describe the preparation and structure of 9,9-dimethyl-9-silafluorene (Me₂SiC₁₂H₈) which was used as a starting material in the synthesis of these 9-ferrocenyl-9-borafluorene derivatives. The title compound was obtained by treatment of 2,2'-dilithio biphenylene with dichlorodimethylsilane Me₂SiCl₂ following a literature procedure (Hudrlik et al., 2006) as indicated in the equation below.

The title compound crystallizes with two almost identical molecules (r.m.s. deviation 0.080Å for all non-H atoms except the methyl groups) in the asymmetric unit (Fig. 1 and 2). All atoms of the silafluorene moiety lie in a common plane (r.m.s. deviation 0.049 Å and 0.035 Å for the two molecules in the asymmetric unit. The Si—C_methyl bonds are considerably shorter [1.865 (4) Å to 1.868 (4) Å] than the Si—C_aromatic bonds [1.882 (3) Å to 1.892 (3) Å]. Due to the strain in the five-membered ring, the innercyclic C—Si—C angle is reduced to 91.05 (14)° and 91.21 (14)°, respectively.

Experimental

A solution of Me₂SiCl₂ (1.9 ml, 2.03 g, 15.8 mmol) and NEt₃ (1.9 ml, 1.38 g, 13.6 mmol) in 50 ml THF was added dropwise to a solution of 2,2'-dilithio biphenylene (14.6 mmol) which was generated from one equivalent of 2,2'-dibrom biphenylene (4.46 g, 14.6 mmol) and two equivalents of nBuLi (28.8 mmol) in 50 ml diethyl ether at 195 K. After stirring for 2 h the solution was filtered. After removing the solvent, the residue was treated with 50 ml water and 30 ml diethyl ether. After removing the diethyl ether from the organic layer, X-ray quality crystals were obtained by sublimation (80%). The NMR spectra were recorded on a Bruker DPX 250 and a Bruker avance 400 spectrometer. 9,9-dimethyl-9-silafluorene: ¹H NMR (CDCl₃, internal TMS): δ 0.43 (s; 6 H, MeSi), δ 7,28 (m; 2 H), δ 7.44 (m; 2 H), δ 7.64 (m; 2 H), δ 7.83 (m; 2 H). ¹³C{¹H}NMR (CDCl₃, internal TMS): δ -3.2 (MeSi), δ 120.8, δ 127.4, δ 130.2, δ 132.7, δ 139.0, δ 140.9.