Methyl 1H-pyrrole-2-carboxylate

The title compound, C6H7NO2, is essentially planar with a dihedral angle of 3.6 (3)° between the pyrrole ring and the methoxycarbonyl O/C/O/C plane. In the crystal structure, the N atom is a hydrogen-bond donor to the carboxylate C=O O atom of the neighboring molecule. These intermolecular hydrogen bonds lead to the formation of helical chains along the b axis.

The title compound, C 6 H 7 NO 2 , is essentially planar with a dihedral angle of 3.6 (3) between the pyrrole ring and the methoxycarbonyl O/C/O/C plane. In the crystal structure, the N atom is a hydrogen-bond donor to the carboxylate C O O atom of the neighboring molecule. These intermolecular hydrogen bonds lead to the formation of helical chains along the b axis.
TK is indebted to the Hanns-Seidel Stiftung for a PhD grant funded by the German Bundesministerium fü r Bildung und Forschung.

Comment
The title compound was prepared, in the attempt to create new complexing ligands, as a byproduct. The compound is quite simular to other compounds already published by our group (Kerscher, Klüfers, Kügel & Müller, 2007;Kerscher, Klüfers & Kügel, 2007).
In the molecule, a formic acid methyl ester is in the 2 position of the pyrrole ring ( Fig. 1). With a torsion angle for C2-C1-C5-O1 of only about 2.9°, the molecule is, with the exception of the H atoms of the methyl group, nearly planar.
Because of this small torsion angle, the molecule is not C s symmetric.
The hydrogen bonds of the nitrogen to the carboxylate oxygen lead to a chain like hydrogen bonding system which can be described according to graph-set analysis (Etter et al., 1990;Bernstein et al., 1995) with a C(5) descriptor on the unitary level [the rpluto program (Cambridge Crystallographic Data Centre, England) was used for the graph set analyses; one of these strands is shown in Fig. 2].
Considering contacts whose range falls below the sum of van der Waals radii by only about 0.1 Å, a set of weak C-H···π interactions leads to the formation of a second system of strands along [0 1 0] which can be described by a C(2) descriptor (see Fig. 3).
The two strand systems alternate, which means two hydrogen bonding strands are interconnected by a strand of weak C-H···π contacts (this situation is illustrated in Fig. 4) and vice versa, two strands made of weak C-H···π contacts are interconnected by hydrogen bonding strands. This bonding pattern leads to sheet like structures normal to [0 0 1].
The molecular packing of the title compound is shown in Figure 5.

Experimental
The title compound was obtained by reaction of 228 mg (3.40 mmol) of pyrrole with 280 mg (1.70 mmol) phosgene imminium chloride in 6 ml of dry acetonitrile. After removal of the solvent, the remaining green solid was purified by column chromatoghraphy on silica with chloroform as eluent. Sublimation of fraction five yielded the title compound as colorless crystals.

Refinement
H atoms were calculated in ideal geometry, with U iso (H) = 1.2U eq (C or N) for all aromatic C-and N-bound H atoms, and with U iso (H) = 1.5U eq (C) for the methylgroup H atoms.
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of the title compound with atom labels and anisotropic displacement ellipsoids (drawn at 50% probability level) for non-H atoms.