Crystal structure of 1-bromo-2-(phenylselenyl)benzene

The first crystal structure determination of 1-bromo-2-(phenylselenyl)benzene is presented. The molecules form weak dimers through displaced parallel π-stacking interactions.


Chemical context
Organoselenium compounds have been found to have diverse scientific applications. For instance, the antioxidant capabilities of the glutathione peroxidases has inspired the synthesis of selenium-containing enzyme mimetics for therapeutic use (Schewe, 1995), and examples are known of selenium-based conjugated materials exhibiting superconductivity (Jé rome et al., 1980). Our research group is interested in organoselenium compounds in the context of designing ligands for coordination to transition metals to generate catalytic complexes. This is an area of growing interest, as examples of seleniumcontaining catalysts with higher activity than the ubiquitous phosphine analogues are discovered (Kumar et al., 2012). The title compound represents a potentially valuable starting material for the synthesis of ligands containing -SePh donor groups, as the ortho-Br atom provides a site of functionalization via, for example, lithium halogen exchange followed by electrophile addition, or a metal-catalyzed cross-coupling reaction. Though previously prepared (Cristau et al., 1985), its structure has remained unreported.

Structural commentary
The molecular structure of the title compound, (I), is depicted in Fig. 1. The asymmetric unit possesses one complete molecule, which features no disorder. The central Se atom exhibits a bent geometry [C1-Se1-C7 = 99.19 (6) ]. The two planes comprising the benzene and phenyl ring C atoms are twisted ISSN 2056-9890 by 72.69 (5) relative to each other. The Br and Se atoms are twisted with respect to the disubstituted benzene ring, as evidenced by displacements in opposite directions from the mean plane of the ring by 0.052 (2) and 0.129 (2) Å , respectively, and the torsion angle Br1-C2-C1-Se1 is 4.2 (1) .
The Se-C distances of 1.9171 (14) and 1.9198 (14) Å are equal within experimental error. At 1.9044 (14) Å , the C-Br distance is measurably shorter than the Se-C bond lengths.

Supramolecular features
The closest intermolecular SeÁ Á ÁBr distance is 3.8013 (3) Å , which lies outside the sum of the van der Waals radii (3.75 Å ) for these two elements (Bondi, 1964). The phenyl group of each molecule is associated with the same group on an adjacent molecule by a slipped -stacking interaction (Fig. 2). The two molecules in the dimeric units are situated about a crystallographic inversion centre. The centroid-to-centroid separation of the aromatic rings is 3.630 (1) Å , while the nearest centroid-to-plane distance is 3.378 (1) Å . Together, these are indicative of the slipped nature of theinteraction. The ring separation is in the normal range (ca 3.3-3.8 Å ) for -stacked interactions (Janiak, 2000). The packing is illustrated in Fig. 3.

Database survey
A search of the Cambridge Structural Database (CSD, Version 5.35; Groom & Allen, 2014) reveals 172 structures featuring two-coordinate aryl-substituted selenium centres. The mean bond angle of 98 (4) and Se-C(aryl) distance of 1.92 (2) Å for these structures match well with the parameters observed for 1-bromo-2-(phenylselenyl)benzene.

Synthesis and crystallization
1-Bromo-2-(phenylselenyl)benzene has been prepared in previous reports using several methodologies, including nickel(II)-catalyzed coupling of NaSePh with 1,2-dibromobenzene (Cristau et al., 1985) and the copper-catalyzed coupling of diphenyl diselenide with 1-bromo-2-iodobenzene (Dandapat et al., 2011), which is the procedure followed for this study (Fig. 4). Purification via flash column chromatography with a silica stationary phase was conducted as reported. Though described by Dandapat et al. (2011) as being a 'slightly brown oil', we found that this compound was a nearly The molecular structure of the title compound, (I), showing 50% probability ellipsoids.

Figure 2
Slipped -stacked dimers of 1-bromo-2-(phenylselenyl)benzene. Each molecule is related to the other by an inversion centre at the centre of the centroid-centroid line.

Figure 3
Packing diagram for (I), viewed along the crystallographic b axis.
colourless liquid which slowly crystallized upon standing at room temperature. NMR spectroscopic analysis matched the reported data.
Though quite soluble in common solvents, including nonpolar solvents such as hexanes, in the highly lipophilic hexamethyldisiloxane we found this substance was only moderately soluble. It crystallized readily as transparent colourless crystals from a solution in this solvent upon storage at 273 K.