(S)-2-[(2-Ammoniophenyl)sulfanylmethyl]pyrrolidinium dibromide

In the title compound, C11H18N2S2+·2Br−, the pyrrolidine ring displays a half-chair conformation, with the flap C atom lying 0.522 (5) Å out of the plane of the other four atoms. The methylene C atom, which connects the pyrrolidinium ring and the thioether group, is displaced from the plane of four pyrrolidinium atoms by 0.690 (6) Å in the same direction as the flap C atom. The plane of four pyrrolidinium atoms is almost perpendicular to the benzene ring [dihedral angle = 75.02 (4)°]. The crystal structure is stabilized by hydrogen bonds between the N and Br atoms.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: PK2105).

Comment
In recent years, the field of asymmetric organocatalysis has developed rapidly, attracting an increasing number of research groups around the world (Seayad & List, 2005). The title compound, readily synthesized from commercially available L-proline and 2-aminobenzenethiol, could act as an organocatalyst in the Michael addition of ketones to nitrostyrenes.
The reaction gave the desired Michael adducts in good yields and high enantioselectivities. The structure of (S)-2-((2ammoniophenylthio)methyl)pyrrolidinium dibromide is shown in Fig. 1.
The crystal is built of doubly protonated cations and bromide anions. The pyrrolidine ring displays a half-chair conformation, with the flap C atom lying 0.522 (5) Å from the remaining four atoms of the pyrrolidine which are almost coplanar.
The methylene C atom, which connects the pyrrolidinium ring and the thioether group, is displaced from the plane of four pyrrolidinium atoms by 0.690 (6) Å in the same direction, as the flap C atom. The plane of four pyrrolidinium ring atoms is almost perpendicular to the benzene ring [dihedral angle 75.02 (4) °]. The crystal structure is stabilized by hydrogen-bonds between the N and Br atoms. The molecular packing of the title compound showing H-bridge interactions between cationic-anionic groups is shown in Fig. 2.

Experimental
The title compound was synthesized by treating 2-aminobenzenethiol (1.25 g,10 mmol) with (S)-2-bromomethylpyrrolidine hydrobromide (2.47 g,10 mmol) in MeCN (30 ml) under stirring at 353 K for 24 h (yield 87%). The compound (S)-2-bromomethylpyrrolidine hydrobromide was obtained from commercially available L-proline by reduction with NaBH 4 and subsequent bromination with PBr 3 (Xu et al., 2006). Suitable crystals of the title compound were obtained by slow evaporation of an ethanol solution at room temperature.

Refinement
All carbon-bonded H atoms were placed in calculated positions with C-H = 0.93 Å (C ar ), C-H = 0.98 Å (R 3 CH), C-H = 0.97 Å (R 2 CH 2 ) and refined using a riding model, with U iso (H)=1.2 eq (C). NH 3 hydrogen atoms were located in a difference map and refined with an N-H distance restraint of 0.83 (1) Å, with U value being 0.06, 0.06, 0.09 respectively, while NH 2 hydrogens were treated using a riding model with N-H distance of 0.90 Å.
supplementary materials sup-2 Figures Fig. 1. The asymmetric unit of the title compound with the atomic labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.