Racemic 1,2,3,4,7,8,9,10-octa­fluoro-6H,12H-5,11-methano­dibenzo[b,f][1,5]diazo­cine: an octa­fluorinated analogue of Tröger’s base

Christophe M L Vande Velde; Delphine Didier; Frank Blockhuys; Sergey Sergeyev

doi:10.1107/S1600536808002602

. 2008 Jan 30;64(Pt 2):o538. doi: 10.1107/S1600536808002602

Racemic 1,2,3,4,7,8,9,10-octafluoro-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine: an octafluorinated analogue of Tröger’s base

Christophe M L Vande Velde ^a, Delphine Didier ^a, Frank Blockhuys ^b, Sergey Sergeyev ^a,^*

PMCID: PMC2960364 PMID: 21201557

Abstract

The title compound, C₁₅H₆F₈N₂, possesses a non-crystallographic twofold axis. The dihedral angle between the two benzene rings is 98.4 (2)°. The crystal structure involves intermolecular C—H⋯F hydrogen bonds.

Related literature

For recent reviews on the chemistry of Tröger’s base (Tröger, 1887 ▶; Spielman, 1935 ▶), see: Valík et al. (2005 ▶) and Dolensky et al. (2007 ▶). For related literature on the chirality of Tröger’s base, see: Prelog & Wieland (1944 ▶); for molecular clefts, see: Wilcox et al. (1987 ▶) and Artacho et al. (2006 ▶) and references cited therein; for (poly)halo-substituted Tröger’s base analogues, see: Jensen & Wärnmark (2001 ▶), Sergeyev & Diederich (2004 ▶), Hansson et al. (2003 ▶), Li et al. (2005 ▶) and Faroughi et al. (2006 ▶). For related literature, see: Zabrodsky et al. (1993 ▶).

Experimental

Crystal data

C₁₅H₆F₈N₂
M _r = 366.22
Monoclinic,
a = 8.075 (3) Å
b = 10.469 (2) Å
c = 17.628 (6) Å
β = 117.15 (2)°
V = 1326.0 (8) Å³
Z = 4
Mo Kα radiation
μ = 0.19 mm⁻¹
T = 290 (1) K
0.3 × 0.2 × 0.2 mm

Data collection

Enraf–Nonius MACH3 diffractometer
Absorption correction: none
5028 measured reflections
2412 independent reflections
1353 reflections with I > 2σ(I)
R _int = 0.078
3 standard reflections every 73 reflections intensity decay: 4%

Refinement

R[F ² > 2σ(F ²)] = 0.044
wR(F ²) = 0.128
S = 1.03
2412 reflections
251 parameters
All H-atom parameters refined
Δρ_max = 0.20 e Å⁻³
Δρ_min = −0.25 e Å⁻³

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994 ▶); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ▶) and Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶) and PLATON (Spek, 2003 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808002602/pk2080sup1.cif

e-64-0o538-sup1.cif^{(18.4KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808002602/pk2080Isup2.hkl

e-64-0o538-Isup2.hkl^{(116.1KB, hkl)}

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

Table 1. C—H ⋯ F contacts (Å, °).

C—H⋯F	C—H	H⋯F	C⋯F	C—H⋯F
C13—H132⋯F10ⁱ	0.93 (3)	2.41 (3)	3.257 (4)	151 (3)
C13—H131⋯F1ⁱⁱ	0.98 (4)	2.46 (3)	3.287 (5)	143 (2)
C12—H122⋯F7ⁱⁱⁱ	0.98 (3)	2.52 (3)	3.336 (4)	141 (3)

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Symmetry codes: (i) Inline graphic , (ii) , (iii) .

Acknowledgments

S. Sergeyev is grateful to Professor Y. Geerts (Université Libre de Bruxelles) for the opportunity to conduct an independent research programme in his laboratory and for generous financial support.

supplementary crystallographic information

Comment

1,2,3,4,7,8,9,10-Octafluoro-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine is a fluorinated derivative of Tröger's base (Tröger, 1887; Spielman, 1935), a polycyclic diamine which is chiral due to severely hindered inversion at the bridgehead N-atoms (Prelog & Wieland, 1944). For recent reviews on its chemistry, see Valík et al. (2005) and Dolensky et al. (2007). Recently, a considerable interest has developed in relatively unfunctionalized receptors with concave aromatic surfaces (termed molecular clefts or tweezers). Wilcox et al. (1987) pioneered the incorporation of the Tröger's base framework in chiral molecular clefts by fusing the methanodiazocine core of Tröger's base with two bicyclic aromatic building blocks. Later, molecular clefts comprising two or three fused methanodiazocine cores have been reported (Artacho et al., 2006, and references cited therein). Our interest in the title compound was raised due to the prospect of using highly fluorinated aromatic systems in the design of molecular clefts, thus providing a possibility to explore different supramolecular interactions.

Synthesis of halo-derivatives of Tröger's base was pioneered by Wärnmark (Jensen & Wärnmark, 2001). Later, a number of fluoro-, chloro-, bromo-, and iodo-derivatives of Tröger's base, with the halogen atoms in different positions on the aromatic rings were reported (Sergeyev & Diederich, 2004 and Hansson et al., 2003). However, they typically contain only one halogen atom on each aromatic ring of the methanodiazocine skeleton. Exceptions are the recently reported 2,4,8,10-tetrafluoro- (Li et al., 2005) and tetrabromo-analogs (Faroughi et al., 2006) of Tröger's base. However, polyhalo-analogs of Tröger's base such as the octafluoro analog presented here are unprecedented. To the best of our knowledge, no X-ray crystal structure of a Tröger's base analog with fluorine in the aromatic ring has been reported.

The racemic octafluoro analog of Tröger's base crystallizes in the centrosymmetric space group P2₁/c with one molecule in the asymmetric unit. The molecule has a non-crystallographic twofold symmetry axis through the bridging carbon C13. The CSM (Continuous Symmetry Measure) is 0.0183 (Zabrodsky et al., 1993). Bond lengths and angles are within expectations. TLS analysis returns quasi-isotropic values for the librational amplitudes, and the values for the resulting corrections of the bond lengths are all below the 2σ level. The dihedral angle between the two benzene rings is 98.4 (2)°, which lies within the normal range for analogs of Tröger's base (Dolensky et al., 2007). Cohesion in the structure appears to be mainly provided by aromatic π-π interactions between the fluorinated benzene rings, leading to pairwise ordering of enantiomers around the centers of inversion, with an interplanar distance of under 4 Å. The most clear examples of this in the structure are Cg(2)···Cg(2)ⁱ (ⁱ=-x,1 - y,1 - z), 3.713 (2) Å, 3.476 (3)Å perp., with a slippage of 1.305 (3) Å, and Cg(1) ··· Cg(1)ⁱⁱ (ⁱⁱ=1 - x,-y,1 - z), 4.805 (2) Å, 3.538 (3)Å perp., with a slippage of 3.251 (3) Å. Cg(x) indicates the centroid of benzene ring x, perp. indicates the perpendicular distance between the ring planes. Due to the lack of suitable hydrogen bond donors, the N-atoms display no close contacts whatsoever. There are a number of F-π contacts in the structure, e.g. F(3)···Cg(2)ⁱⁱ 3.672 (3) Å, C3—F3···Cg(2)ⁱⁱ 161.7 (2)°. Also, H—F contacts occur that are substantially shorter than the van der Waals radii, but these are not usually understood as hydrogen bonds. They are given in Table 1.

Experimental

2,3,4,5-Tetrafluoroaniline (330 mg, 2 mmol) and paraformaldehyde (120 mg, 4 mmol) were added under vigorous stirring to CF₃COOH (4 ml) at -15°C. The resulting mixture was allowed to reach room temperature and stirred for 14 days, then slowly added to a stirred mixture of ice and 30% aqueous NH₃ (7 ml). Extraction with CH₂Cl₂ (2 x 20 ml), drying of the organic layer over MgSO₄, and removal of the solvent in vacuo gave a crude product which was purified by flash chromatography (SiO₂/CH₂Cl₂). Yield of the title compound: 135 mg (37%). Crystals suitable for X-ray diffraction were grown by slow evaporation from CHCl₃solution.

¹H NMR (300 MHz, CDCl₃, 25°C): d = 4.20–4.30 (m, 4H, H61, H62, H121, H122), 4.50 (d, J = 17.5 Hz, 2H, H131, H132); ¹³C NMR (75 MHz, CDCl₃, 25°C): d = 50.1, 66.5, 111.9 (ddt, J =17.7, 3.4, 1.7 Hz), 130.8 (dddd, J = 10.6, 5.2, 3.7, 1.9 Hz), 137.3 (dddd, J = 252.0, 16.5, 13.0, 3.1 Hz), 140.2 (dddd, J = 251.3, 14.9, 13.0, 5.0 Hz), 141.7 (dddd, J = 248.2, 11.2, 4.1, 1.3 Hz), 144.0 (ddt, J = 245.2, 10.9, 3.7 Hz). HR—EI—MS: m/z: calcd. for C₁₅H₆F₈N₂ ([M]⁺): 366.0403; found: 366.0405.