research communications
of 2,2′-bipyrrole
aDepartment of Chemistry and Biochemistry, Eastern Washington University, Science 226, Cheney, WA 99004, USA, and bDepartment of Chemistry, 1253 University of Oregon, Eugene, Oregon 97403, USA
*Correspondence e-mail: alamm@ewu.edu
The complete molecule of the title compound, C8H8N2, is generated by a crystallographic center of symmetry. In the crystal, short N—H⋯π [H⋯π = 2.499 (19) Å] interactions link the molecules into a herringbone structure.
Keywords: crystal structure; bipyrrole; N—H⋯π interactions; herringbone structure.
CCDC reference: 1575394
1. Chemical context
Bipyrrole, C8H8N2, has been studied extensively over the years: the first reported synthesis was in 1962 (Rapoport & Castagnoli, 1962). The bipyrrole core occurs in naturally occurring compounds such as prodigiosin (Wasserman et al., 1960). Functionalized bipyrroles have been shown to have anti-cancer activity (Manderville, 2001). Corrole rings contain a bipyrrole segment in the macrocycle (Aviv-Harel & Gross, 2009). Herein, we report on the of the title compound, (I), synthesized by the of pyrrole.
2. Structural commentary
The complete molecule of (I) is generated by a crystallographic center of symmetry (Fig. 1), and therefore the pyrrole rings are exactly parallel and the N—H groups face in opposite directions. The C2—C3 bond in (I) is 1.4151 (19) Å, versus the equivalent bond in pyrrole, which has a length of 1.423 (3) Å. The double bonds C1=C2 and C3=C4 in (I) are 1.3635 (19) and 1.3767 (17) Å, respectively, versus the double-bond length in pyrrole of 1.357 Å. The shortening of the C2—C3 bond and the lengthening of the adjacent C=C double bonds in (I) compared to pyrrole is consistent with stronger intermolecular interactions (see below).
3. Supramolecular features
In the crystal of (I), the molecules adopt an edge-to-face orientation: the distance between the N—H group and the centroid of the adjacent pyrrole ring generated by the 21 screw axis is 2.499 (19) Å (Table 1). A survey of the Cambridge Crystallographic Database (Groom et al., 2016) showed that the average N—H⋯π separation is 2.804 Å and 13 out of 156 interactions (8.3%) had an N—H⋯π interactions shorter than 2.5 Å. The crystal packing in (I) is similar to that of pyrrole, which has the same intermolecular N—H⋯π interactions (Goddard et al., 1997). The edge-to-face interaction has been suggested to be a stabilizing factor in protein structures and have been observed to have a separation of 2.42 Å from the N—H group to the phenyl ring (Steiner, 1998) and calculations corroborate these data (Levitt Perutz, 1988). It is notable that the N—H bond of 2,2′-bipyrrole points almost directly at the midpoint of the C2—C3 bond. In the extended structure, the molecules are orientated by edge-to-face interactions generating a herringbone pattern, see Fig. 2.
4. Database survey
There are very few examples of similar compounds available in the literature. Most bipyrroles have carbonyl groups as substituents on the pyrrole ring in which the N—H group forms hydrogen bonds with the oxygen atom of the carbonyl (Okawara et al., 2015). So far as we are aware, there are no bipyrrole examples that exhibit the same packing and hydrogen-bonding pattern as the title compound; the closest example is pyrrole itself (Goddard et al., 1997).
5. Synthesis and crystallization
230 µl (3.3 mmol) of pyrrole was added to dichloromethane (10 ml), degassed and cooled to 195 K. Trimethylsilyl bromide (290 µl, 2.2 mmol) and phenyl iodine trifluoracetic acid (477 mg, 1.1 mmol in 1 ml dichloromethane) were added quickly to the cooled reaction. The mixture was stirred for 1 h then extracted with a saturated sodium bicarbonate solution and purified by were obtained 7 d later by slow evaporation from an ethyl acetate solution.
with a pentane/ethyl acetate (1:1) solution. Colourless blocks of (I)6. Refinement
Crystal data, data collection and structure . The H atoms were located in difference maps and refined with isotropic displacement parameters.
details are summarized in Table 2Supporting information
CCDC reference: 1575394
https://doi.org/10.1107/S2056989017013433/hb7692sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989017013433/hb7692Isup2.hkl
Survey of the Cambridge Database NH-pi bond lengths. DOI: https://doi.org/10.1107/S2056989017013433/hb7692sup3.pdf
Data collection: APEX2 (Bruker, 2004); cell
SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHEXLTL (Sheldrick, 2008).C8H8N2 | F(000) = 140 |
Mr = 132.16 | Dx = 1.302 Mg m−3 |
Monoclinic, P21/c | Cu Kα radiation, λ = 1.54178 Å |
a = 5.9500 (2) Å | Cell parameters from 1086 reflections |
b = 6.7650 (2) Å | θ = 7.5–66.5° |
c = 8.4363 (3) Å | µ = 0.64 mm−1 |
β = 96.746 (2)° | T = 173 K |
V = 337.22 (2) Å3 | Cut-block, colorless |
Z = 2 | 0.11 × 0.10 × 0.06 mm |
Bruker APEXII CCD diffractometer | 540 reflections with I > 2σ(I) |
Radiation source: Incoatec IµS | Rint = 0.026 |
φ and ω scans | θmax = 66.5°, θmin = 7.5° |
Absorption correction: multi-scan (SADABS; Bruker, 2004) | h = −7→4 |
Tmin = 0.666, Tmax = 0.753 | k = −7→8 |
1989 measured reflections | l = −9→10 |
590 independent reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Hydrogen site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.034 | All H-atom parameters refined |
wR(F2) = 0.098 | w = 1/[σ2(Fo2) + (0.0657P)2 + 0.034P] where P = (Fo2 + 2Fc2)/3 |
S = 1.08 | (Δ/σ)max < 0.001 |
590 reflections | Δρmax = 0.18 e Å−3 |
62 parameters | Δρmin = −0.16 e Å−3 |
0 restraints |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
N1 | 0.53346 (18) | 1.09945 (15) | 0.20670 (12) | 0.0322 (4) | |
C1 | 0.7071 (2) | 1.07425 (18) | 0.32546 (15) | 0.0352 (4) | |
C2 | 0.8665 (2) | 0.95786 (18) | 0.26832 (16) | 0.0330 (4) | |
C3 | 0.7857 (2) | 0.91019 (17) | 0.10841 (15) | 0.0297 (4) | |
C4 | 0.57828 (19) | 0.99966 (16) | 0.07196 (13) | 0.0263 (4) | |
H1 | 0.704 (2) | 1.135 (2) | 0.4292 (17) | 0.043 (4)* | |
H1N | 0.407 (2) | 1.170 (3) | 0.2168 (17) | 0.046 (4)* | |
H2 | 1.010 (3) | 0.916 (2) | 0.3269 (19) | 0.041 (4)* | |
H3 | 0.859 (2) | 0.831 (2) | 0.0354 (16) | 0.039 (4)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0364 (6) | 0.0295 (6) | 0.0299 (6) | 0.0075 (4) | 0.0010 (5) | −0.0030 (4) |
C1 | 0.0424 (8) | 0.0320 (7) | 0.0296 (7) | 0.0003 (5) | −0.0028 (6) | −0.0038 (5) |
C2 | 0.0299 (7) | 0.0329 (7) | 0.0347 (7) | −0.0016 (5) | −0.0023 (5) | 0.0043 (5) |
C3 | 0.0278 (7) | 0.0307 (7) | 0.0312 (7) | 0.0005 (5) | 0.0055 (5) | 0.0021 (5) |
C4 | 0.0306 (6) | 0.0217 (6) | 0.0270 (6) | −0.0017 (4) | 0.0055 (5) | 0.0025 (4) |
N1—C1 | 1.3628 (18) | C2—C3 | 1.4151 (19) |
N1—C4 | 1.3748 (15) | C2—H2 | 0.979 (16) |
N1—H1N | 0.907 (16) | C3—C4 | 1.3767 (17) |
C1—C2 | 1.3635 (19) | C3—H3 | 0.959 (14) |
C1—H1 | 0.970 (15) | C4—C4i | 1.441 (2) |
C1—N1—C4 | 110.02 (11) | C3—C2—H2 | 126.4 (9) |
C1—N1—H1N | 124.3 (9) | C4—C3—C2 | 107.93 (11) |
C4—N1—H1N | 125.6 (9) | C4—C3—H3 | 124.4 (8) |
N1—C1—C2 | 108.12 (11) | C2—C3—H3 | 127.6 (8) |
N1—C1—H1 | 121.2 (9) | N1—C4—C3 | 106.69 (11) |
C2—C1—H1 | 130.7 (9) | N1—C4—C4i | 121.74 (13) |
C1—C2—C3 | 107.23 (11) | C3—C4—C4i | 131.57 (13) |
C1—C2—H2 | 126.4 (9) | ||
C4—N1—C1—C2 | 0.11 (14) | C1—N1—C4—C4i | 179.68 (12) |
N1—C1—C2—C3 | −0.15 (14) | C2—C3—C4—N1 | −0.07 (13) |
C1—C2—C3—C4 | 0.13 (14) | C2—C3—C4—C4i | −179.73 (15) |
C1—N1—C4—C3 | −0.03 (13) |
Symmetry code: (i) −x+1, −y+2, −z. |
Cg is the centroid of the N1/C1–C4 ring. |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1N···Cg1ii | 0.907 (16) | 2.499 (19) | 3.2275 (12) | 138.1 (13) |
Symmetry code: (ii) −x+1, y+1/2, −z+1/2. |
Acknowledgements
The authors are grateful for the generous support from EWU's Faculty Grants for Research and Creative Works and support from EWU's Department of Chemistry and Biochemistry.
References
Aviv-Harel, I. & Gross, Z. (2009). Chem. Eur. J. 15, 8382–8394. PubMed CAS
Bruker (2004). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.
Goddard, R., Heinemann, O. & Krüger, C. (1997). Acta Cryst. C53, 1846–1850. Web of Science CSD CrossRef CAS IUCr Journals
Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171–179. Web of Science CSD CrossRef IUCr Journals
Levitt, M. & Perutz, M. F. (1988). J. Mol. Biol. 201, 751–754. CrossRef CAS PubMed Web of Science
Manderville, R. A. (2001). Curr. Med. Chem. Anti-Cancer Agents, 1, 195–218. CrossRef PubMed CAS
Okawara, T., Doi, A., Ono, T., Abe, M., Takehara, K., Hisaeda, Y. & Matsushima, S. (2015). Tetrahedron Lett. 56, 1407–1410. CSD CrossRef CAS
Rapoport, H. & Castagnoli, N. (1962). J. Am. Chem. Soc. 84, 2178–2181. CrossRef CAS Web of Science
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals
Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals
Steiner, T. (1998). Acta Cryst. D54, 584–588. Web of Science CrossRef CAS IUCr Journals
Wasserman, H. H., McKeon, J. E., Smith, L. & Forgione, P. (1960). J. Am. Chem. Soc. 82, 506–507. CrossRef CAS
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