2,2′-(Propane-2,2-di­yl)bis­(1H-pyrrole)

Guillaume Journot; Reinhard Neier; Helen Stoeckli-Evans

doi:10.1107/S1600536809054701

. 2010 Jan 16;66(Pt 2):o392. doi: 10.1107/S1600536809054701

2,2′-(Propane-2,2-diyl)bis(1H-pyrrole)

Guillaume Journot ^a, Reinhard Neier ^a,^*, Helen Stoeckli-Evans ^b

PMCID: PMC2979882 PMID: 21579813

Abstract

The title compound, C₁₁H₁₄N₂, crystallized with two independent molecules (A and B) in the asymmetric unit. The two molecules differ only slightly, with the pyrrole rings being inclined to one another at a dihedral angle of 87.67 (8)° in molecule A and 88.09 (7)° in molecule B. In the crystal, there are no classical hydrogen bonds, but the two pyrrole NH groups of one molecule are involved in N—H⋯π interactions with the pyrrole rings of the other molecule. In this manner, a compact box-like arrangement of the two independent molecules is formed.

Related literature

For substituted calix[4]pyrroles, see: Gale et al. (1998 ▶); Sessler & Davis (2001 ▶); Sessler et al. (2003 ▶). For the synthesis and crystal structure of meso-diethyl-bis(2-pyrrolyl)methane, see: Sobral et al. (2003 ▶). For intermolecular interactions involving aromatic rings in biological systems, see: Meyer et al. (2003 ▶). For a spectroscopic analysis of N—H⋯π interactions in pyrroles, see: Dauster et al. (2008 ▶).

Experimental

Crystal data

C₁₁H₁₄N₂
M _r = 174.24
Triclinic,
a = 8.4554 (8) Å
b = 9.2001 (8) Å
c = 13.2274 (11) Å
α = 99.802 (7)°
β = 95.321 (7)°
γ = 97.328 (7)°
V = 998.74 (15) Å³
Z = 4
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 173 K
0.40 × 0.34 × 0.28 mm

Data collection

Stoe IPDS-2 diffractometer
15270 measured reflections
5385 independent reflections
3816 reflections with I > 2σ(I)
R _int = 0.046

Refinement

R[F ² > 2σ(F ²)] = 0.045
wR(F ²) = 0.106
S = 1.02
5385 reflections
255 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.25 e Å⁻³
Δρ_min = −0.21 e Å⁻³

Data collection: X-AREA (Stoe & Cie, 2009 ▶); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2009 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶) and Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536809054701/is2506sup1.cif

e-66-0o392-sup1.cif^{(21.8KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809054701/is2506Isup2.hkl

e-66-0o392-Isup2.hkl^{(263.7KB, hkl)}

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

Table 1. Geometry of N—H⋯π interactions (Å, °).

D	H	Centroid	N—H	H⋯Cg	D⋯Cg	N—H⋯Cg
N1	H1N	Cg4	0.86 (2)	2.534 (17)	3.2190 (12)	137.4 (14)
N2	H2N	Cg3	0.86 (2)	2.591 (17)	3.2425 (12)	133.7 (13)
N21	H21N	Cg1	0.88 (2)	2.523 (16)	3.1925 (12)	133.9 (12)
N22	H22N	Cg2	0.86 (2)	2.610 (17)	3.2440 (12)	131.3 (13)

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Cg1, Cg2, Cg3 and Cg4 are the centroids of the N1/C1–C4, N2/C5–C8, N21/C21—C24 and N22/C25–C28 rings, respectively.

Acknowledgments

HSE is grateful to the XRD Application LAB, Microsystems Technology Division, Swiss Center for Electronics and Microtechnology, Neuchâtel, for access to the X-ray diffraction equipment.

supplementary crystallographic information

Comment

The title compound was prepared as a building block for the formation of substituted calix[4]pyrroles. The latter have been shown to form extremely interesting host–guest complexes with various anions (Gale et al., 1998; Sessler & Davis, 2001; Sessler et al., 2003).

The structure of the title compound is shown in Fig. 1, and the geometrical parameters are given in the Supplementary Information and the archived CIF. The compound crystallized in the centrosymmetric triclinic space group P1 with two independent molecules (A and B) in the asymmetric unit. The bond lengths and angles are similar to those observed in the diethyl analogue (Sobral et al., 2003), which also crystallized with two independent molecules, but in the non-centrosymetric monoclinic space group C2.

In the title compound the quateranry centers, C9 in A and C29 in B, impose a twist to the molecules with the pyrrole ring mean-planes being almost perpendicular to one another; 87.67 (8) ° in molecule A and 88.09 (7)° in molecule B. This is similar to the situation in the diethyl analogue where the two dihedral angles are 86.5 (2) and 86.7 (2) °.

N—H···π interactions are extremely important in biological systems and this aspect as been reviewed by (Meyer et al., 2003). The spectroscopic aspects of the N—H···π interactions of the pyrrole dimer have also been studied recently by (Dauster et al., 2008). In the crystal of the title compound the two independent molecules are linked by N—H···π interactions involving the pyrrole NH H-atoms of molecule A with the pyrrole rings of molecule B, and visa-versa (Table 1). This leads to the formation of a compact box-like arrangement of the two molecules, as shown in Fig. 2. Again this arrangement is similar to that observed in the crystal of the diethyl analogue.

Experimental

A mixture of acetone (4.21 ml, 57.4 mmol) and pyrrole (31.72 ml, 0.459 mol, 8 equiv.) were stirred for 5 min and then trifluoroactetic acid (TFA: 0.44 ml, 2.53 mmol, 0.1 equiv) was added. The mixture stirred for an additional 5 min and then quenched with aqueous NaOH (0.1 N, 30 ml). It was then extracted with CH₂Cl₂ (50 ml × 2) and the organic layer dried (Na₂SO₄). The solvent was removed in vacuo and the remaining oil (82% pure in GC) was purified by flash chromatography on silica (eluent: cyclohexane/ethyl acetate; v:v = 4:1) to give colourless block-like crystals of the title compound (yield 6.8 g, 68%). ¹H NMR (CDCl₃): δ 7.72 (bs, 2H, N—H), 6.62–6.60 (m, 2H, pyrrolic-H1), 6.15–6.13 (m, 2H, pyrrolic-H2), 6.11–6.09 (m, 2H, pyrrolic-H3), 1.59 (s, 6H, –CH₃); ¹³CNMR (CDCl₃): δ 139.24 (C4), 117.19 (C1), 107.91 (C2), 103.87 (C3), 35.52(C5), 29.46 (C6).