2,8-Dichloro-6H,12H-5,11-methano­dibenzo[b,f][1,5]diazo­cine

In the mol­ecule of the title compound, C₁₅H₁₂Cl₂N₂, the 2,8-dichloro analogue of Tröger's base, the two aryl rings are offset with respect to one another by virtue of the diazo­cine bridge. The dihedral angle between the two benzene rings is 95.64 (3)°.

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma](C-C)= 0.002 Å
• R factor = 0.030
• wR factor = 0.077
• Data-to-parameter ratio = 17.7

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S1. Comment

Tröger's base was the first chiral compound to be successfully resolved whose optical activity was the result of stereogenic tertiary nitrogen centres. This resolution was achieved through what may have been the first example of a chiral separation using chromatography with a chiral stationary phase (Prelog & Wieland, 1944). An important feature of this family of molecules is the

diazocine bridge that imparts a twist within the compounds such that the two aryl rings are offset with respect to one another. The angle made by the intersection of two least squares planes (as defined by the aryl rings) is referred to as the dihedral angle. This dihedral angle has been measured across a range of compounds to lie between 82° (Solano et al., 2005) and 108.44 (4)° (Faroughi et al., 2006b) for simple dibenzo Tröger's base analogues, and is dependent upon the nature of the substituents on the aromatic rings. We have previously reported that the dihedral angle in 2,8-dibromo Tröger's base is 94.45 (4)° (Faroughi et al., 2006a) and now report that the title compound, (I), has a very similar structure.

We were interested in preparing a range of dihalo Tröger's base analogues as precursors for supramolecular recognition elements. The synthesis of (I) in racemic form was achieved by reacting 4-chloroaniline with paraformaldehyde in trifluoroacetic acid (TFA).

In the molecule of the title compound, (I), the bond lengths and angles are within normal ranges (Allen et al., 1987). Rings B (N1/N2/C1/C6/C7/C15) and C (N1/N2/C8/C13—C15) are not planar, having total puckering amplitudes, Q_T, of 1.376 (3) and 0.741 (3) Å, respectively and twist conformations φ = -115.97 (3)°, θ = 108.20 (2)° and φ = -31.28 (3)°, θ = 48.67 (3)° (Cremer & Pople, 1975). Rings A (C1—C6) and D (C8—C13) are, of course, planar and the dihedral angle between them is 95.64 (3)°.

Related literature

For general background, see: Prelog & Wieland (1944); Allen et al. (1987); Cremer & Pople (1975); Jensen & Wärnmark (2001). For related literature, see: Solano et al. (2005); Faroughi et al. (2006a,b).

S2. Experimental

The title compound was prepared according to a literature procedure (Jensen & Wärnmark, 2001) in 87% yield and recrystallized from chloroform solution.

S3. Refinement

H atoms were positioned geometrically, with C—H = 0.95 and 0.99 Å for aromatic and methylene H atoms, respectively, and constrained to ride on their parent atoms, with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT and XPREP (Siemens, 1995); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: TEXSAN for Windows (Molecular Structure Corporation, 1998), Xtal3.6 (Hall et al., 1999), ORTEPII (Johnson, 1976) and WinGX (Farrugia, 1999); software used to prepare material for publication: WinGX.

Figures

	Fig. 1. The molecular structure of (I) with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. Reaction scheme.

2,8-Dichloro-6H,12H-5,11- methanodibenzo[b,f][1,5]diazocine

Crystal data

C15H12Cl2N2	Z = 2
Mr = 291.17	F(000) = 300
Triclinic, P1	Dx = 1.469 Mg m^−3
Hall symbol: -P 1	Melting point: 402.49 K
a = 6.3017 (18) Å	Mo Kα radiation, λ = 0.71073 Å
b = 10.203 (3) Å	Cell parameters from 868 reflections
c = 10.685 (3) Å	θ = 2.7–28.3°
α = 83.059 (5)°	µ = 0.48 mm^−1
β = 77.303 (4)°	T = 150 K
γ = 80.297 (5)°	Prism, colorless
V = 658.1 (3) Å^3	0.40 × 0.30 × 0.25 mm

Data collection

Siemens SMART 1000 CCD diffractometer	3041 independent reflections
Radiation source: sealed tube	2845 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.028
ω scans	θmax = 28.3°, θmin = 2.0°
Absorption correction: gaussian [GAUSSIAN (Coppens et al., 1965) and XPREP (Siemens, 1995)]	h = −8→8
Tmin = 0.838, Tmax = 0.887	k = −13→13
6481 measured reflections	l = −13→14

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.030	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.077	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.03P)^2 + 0.3P] where P = (Fo^2 + 2Fc^2)/3
3041 reflections	(Δ/σ)max = 0.001
172 parameters	Δρmax = 0.39 e Å^−3
0 restraints	Δρmin = −0.31 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq
Cl1	0.13871 (6)	0.53475 (3)	−0.23138 (3)	0.03051 (10)
Cl2	−0.36576 (6)	0.31732 (4)	0.63832 (3)	0.03694 (11)
N1	0.21497 (17)	0.04929 (10)	0.13464 (10)	0.0225 (2)
N2	0.43312 (17)	0.15300 (11)	0.24498 (10)	0.0237 (2)
C1	0.19385 (19)	0.16949 (12)	0.05035 (11)	0.0202 (2)
C2	0.0451 (2)	0.18494 (12)	−0.03192 (12)	0.0223 (2)
H2	−0.0435	0.1174	−0.0287	0.027*
C3	0.0246 (2)	0.29694 (12)	−0.11795 (12)	0.0235 (2)
H3	−0.0790	0.3076	−0.1723	0.028*
C4	0.1586 (2)	0.39335 (12)	−0.12326 (11)	0.0231 (2)
C5	0.3063 (2)	0.38015 (13)	−0.04268 (12)	0.0244 (2)
H5	0.3972	0.4469	−0.0483	0.029*
C6	0.32302 (19)	0.26959 (12)	0.04676 (11)	0.0216 (2)
C7	0.4719 (2)	0.26153 (14)	0.14220 (12)	0.0257 (3)
H7A	0.6272	0.2467	0.0961	0.031*
H7B	0.4461	0.3475	0.1812	0.031*
C8	0.2378 (2)	0.18853 (12)	0.33978 (11)	0.0210 (2)
C9	0.2439 (2)	0.27932 (13)	0.42655 (12)	0.0247 (3)
H9	0.3760	0.3145	0.4222	0.030*
C10	0.0598 (2)	0.31846 (13)	0.51862 (12)	0.0264 (3)
H10	0.0639	0.3807	0.5770	0.032*
C11	−0.1310 (2)	0.26523 (13)	0.52427 (12)	0.0253 (3)
C12	−0.1417 (2)	0.17465 (12)	0.44002 (12)	0.0236 (2)
H12	−0.2736	0.1387	0.4463	0.028*
C13	0.0435 (2)	0.13667 (11)	0.34567 (11)	0.0206 (2)
C14	0.0297 (2)	0.04557 (12)	0.24619 (12)	0.0227 (2)
H14A	0.0304	−0.0471	0.2865	0.027*
H14B	−0.1104	0.0735	0.2163	0.027*
C15	0.4179 (2)	0.03436 (13)	0.18434 (13)	0.0266 (3)
H15A	0.4225	−0.0444	0.2482	0.032*
H15B	0.5462	0.0184	0.1127	0.032*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.04063 (19)	0.02569 (16)	0.02488 (16)	−0.00416 (13)	−0.00813 (13)	0.00082 (12)
Cl2	0.03147 (19)	0.0498 (2)	0.02675 (17)	0.00243 (15)	−0.00157 (13)	−0.01223 (14)
N1	0.0245 (5)	0.0207 (5)	0.0233 (5)	−0.0005 (4)	−0.0072 (4)	−0.0045 (4)
N2	0.0211 (5)	0.0275 (5)	0.0236 (5)	−0.0012 (4)	−0.0071 (4)	−0.0048 (4)
C1	0.0206 (6)	0.0204 (5)	0.0190 (5)	−0.0002 (4)	−0.0023 (4)	−0.0065 (4)
C2	0.0230 (6)	0.0226 (6)	0.0226 (6)	−0.0032 (4)	−0.0047 (4)	−0.0075 (4)
C3	0.0236 (6)	0.0270 (6)	0.0209 (6)	−0.0010 (5)	−0.0062 (5)	−0.0064 (5)
C4	0.0274 (6)	0.0223 (6)	0.0180 (5)	−0.0013 (5)	−0.0027 (4)	−0.0029 (4)
C5	0.0255 (6)	0.0268 (6)	0.0222 (6)	−0.0080 (5)	−0.0027 (5)	−0.0046 (5)
C6	0.0185 (5)	0.0270 (6)	0.0198 (5)	−0.0032 (4)	−0.0023 (4)	−0.0065 (4)
C7	0.0213 (6)	0.0340 (7)	0.0236 (6)	−0.0078 (5)	−0.0051 (5)	−0.0029 (5)
C8	0.0222 (6)	0.0218 (5)	0.0198 (5)	−0.0011 (4)	−0.0079 (4)	−0.0007 (4)
C9	0.0278 (6)	0.0259 (6)	0.0232 (6)	−0.0051 (5)	−0.0106 (5)	−0.0017 (5)
C10	0.0350 (7)	0.0252 (6)	0.0207 (6)	−0.0014 (5)	−0.0101 (5)	−0.0045 (5)
C11	0.0278 (6)	0.0278 (6)	0.0179 (5)	0.0018 (5)	−0.0044 (5)	−0.0016 (5)
C12	0.0242 (6)	0.0250 (6)	0.0216 (6)	−0.0041 (5)	−0.0066 (5)	0.0016 (5)
C13	0.0246 (6)	0.0187 (5)	0.0194 (5)	−0.0024 (4)	−0.0079 (4)	−0.0001 (4)
C14	0.0266 (6)	0.0205 (5)	0.0229 (6)	−0.0055 (5)	−0.0072 (5)	−0.0026 (4)
C15	0.0251 (6)	0.0259 (6)	0.0291 (6)	0.0038 (5)	−0.0094 (5)	−0.0072 (5)

Geometric parameters (Å, º)

Cl1—C4	1.7411 (13)	C6—C7	1.5170 (17)
Cl2—C11	1.7477 (13)	C7—H7A	0.9900
N1—C1	1.4366 (16)	C7—H7B	0.9900
N1—C15	1.4678 (17)	C8—C9	1.3981 (17)
N1—C14	1.4754 (16)	C8—C13	1.3997 (17)
N2—C8	1.4362 (16)	C9—C10	1.3821 (19)
N2—C15	1.4663 (16)	C9—H9	0.9500
N2—C7	1.4736 (17)	C10—C11	1.388 (2)
C1—C2	1.3983 (17)	C10—H10	0.9500
C1—C6	1.4014 (17)	C11—C12	1.3847 (18)
C2—C3	1.3841 (18)	C12—C13	1.3975 (17)
C2—H2	0.9500	C12—H12	0.9500
C3—C4	1.3888 (18)	C13—C14	1.5191 (16)
C3—H3	0.9500	C14—H14A	0.9900
C4—C5	1.3813 (18)	C14—H14B	0.9900
C5—C6	1.3930 (18)	C15—H15A	0.9900
C5—H5	0.9500	C15—H15B	0.9900
C1—N1—C15	110.57 (10)	C9—C8—C13	119.88 (11)
C1—N1—C14	112.99 (9)	C9—C8—N2	118.21 (11)
C15—N1—C14	107.69 (10)	C13—C8—N2	121.90 (11)
C8—N2—C15	111.00 (10)	C10—C9—C8	120.66 (12)
C8—N2—C7	111.85 (10)	C10—C9—H9	119.7
C15—N2—C7	107.72 (10)	C8—C9—H9	119.7
C2—C1—C6	119.56 (11)	C9—C10—C11	118.88 (12)
C2—C1—N1	119.08 (11)	C9—C10—H10	120.6
C6—C1—N1	121.34 (11)	C11—C10—H10	120.6
C3—C2—C1	121.12 (11)	C12—C11—C10	121.75 (12)
C3—C2—H2	119.4	C12—C11—Cl2	119.29 (10)
C1—C2—H2	119.4	C10—C11—Cl2	118.95 (10)
C2—C3—C4	118.68 (12)	C11—C12—C13	119.36 (12)
C2—C3—H3	120.7	C11—C12—H12	120.3
C4—C3—H3	120.7	C13—C12—H12	120.3
C5—C4—C3	121.10 (12)	C12—C13—C8	119.47 (11)
C5—C4—Cl1	119.04 (10)	C12—C13—C14	120.04 (11)
C3—C4—Cl1	119.85 (10)	C8—C13—C14	120.41 (11)
C4—C5—C6	120.48 (12)	N1—C14—C13	111.62 (10)
C4—C5—H5	119.8	N1—C14—H14A	109.3
C6—C5—H5	119.8	C13—C14—H14A	109.3
C5—C6—C1	118.99 (11)	N1—C14—H14B	109.3
C5—C6—C7	120.05 (11)	C13—C14—H14B	109.3
C1—C6—C7	120.90 (11)	H14A—C14—H14B	108.0
N2—C7—C6	111.91 (10)	N2—C15—N1	111.81 (10)
N2—C7—H7A	109.2	N2—C15—H15A	109.3
C6—C7—H7A	109.2	N1—C15—H15A	109.3
N2—C7—H7B	109.2	N2—C15—H15B	109.3
C6—C7—H7B	109.2	N1—C15—H15B	109.3
H7A—C7—H7B	107.9	H15A—C15—H15B	107.9
C15—N1—C1—C2	163.66 (10)	C15—N2—C8—C13	−15.32 (15)
C14—N1—C1—C2	−75.55 (13)	C7—N2—C8—C13	105.03 (13)
C15—N1—C1—C6	−14.71 (15)	C13—C8—C9—C10	0.13 (18)
C14—N1—C1—C6	106.08 (12)	N2—C8—C9—C10	179.10 (11)
C6—C1—C2—C3	0.66 (17)	C8—C9—C10—C11	0.54 (19)
N1—C1—C2—C3	−177.73 (10)	C9—C10—C11—C12	−0.22 (19)
C1—C2—C3—C4	1.33 (18)	C9—C10—C11—Cl2	−178.62 (10)
C2—C3—C4—C5	−1.45 (18)	C10—C11—C12—C13	−0.75 (19)
C2—C3—C4—Cl1	179.45 (9)	Cl2—C11—C12—C13	177.65 (9)
C3—C4—C5—C6	−0.44 (19)	C11—C12—C13—C8	1.40 (18)
Cl1—C4—C5—C6	178.66 (9)	C11—C12—C13—C14	−175.40 (11)
C4—C5—C6—C1	2.44 (18)	C9—C8—C13—C12	−1.10 (17)
C4—C5—C6—C7	−174.95 (11)	N2—C8—C13—C12	179.97 (11)
C2—C1—C6—C5	−2.54 (17)	C9—C8—C13—C14	175.69 (11)
N1—C1—C6—C5	175.82 (10)	N2—C8—C13—C14	−3.24 (17)
C2—C1—C6—C7	174.83 (11)	C1—N1—C14—C13	−74.78 (13)
N1—C1—C6—C7	−6.81 (17)	C15—N1—C14—C13	47.63 (13)
C8—N2—C7—C6	−77.31 (13)	C12—C13—C14—N1	162.98 (10)
C15—N2—C7—C6	44.93 (13)	C8—C13—C14—N1	−13.79 (15)
C5—C6—C7—N2	168.04 (11)	C8—N2—C15—N1	52.32 (14)
C1—C6—C7—N2	−9.29 (16)	C7—N2—C15—N1	−70.44 (13)
C15—N2—C8—C9	165.73 (11)	C1—N1—C15—N2	53.76 (14)
C7—N2—C8—C9	−73.93 (14)	C14—N1—C15—N2	−70.13 (13)