Crystal structures of 1-bromo-3,5-bis(4,4-dimethyl-1,3-oxazolin-2-yl)benzene 0.15-hydrate and 3,5-bis(4,4-dimethyl-1,3-oxazolin-2-yl)-1-iodobenzene

The isostructural 1-bromo and 1-iodo derivatives of 3,5-bis(1,3-oxazolin-2-yl)benzene show supramolecular features of (non-classical) hydrogen bonding, parallel-displaced π–π interactions, and close N⋯I contacts. The former was found to crystallize as a sub-hydrate.

There are many examples for respective organometallic complexes of transition and rare-earth metals known in the literature with many of them bearing chiral 2-oxazolinyl substituents within the Phebox ligand. Exemplary compounds include those of some early transition metals (Chuchuryukin et al., 2011), iridium , or palladium (Lu et al., 2010), to name but a few.
The substitution with bromine and iodine renders the title compounds capable of being utilized as potential precursors for C-C cross-coupling building blocks bearing the Phebox motif. ISSN 2056-9890
Compound (1) crystallized from water-containing acetonitrile as an adduct with 0.15 H 2 O in the monoclinic space group P2 1 /n. Within the molecular structure ( Fig. 1) the 2-oxazolinyl functional groups are oriented antiperiplanar to each other. The elongated displacement ellipsoid of the methylene carbon atom C13 indicates a noteworthy vibrational freedom orthogonal to plane C which was not observed for atoms within ring A. The absence of a comparable displacement component of C14 perpendicular to plane C disagrees with pseudorotational disorder around the atomic positions mentioned.
The isostructural iodo derivative (2) was crystallized from dichloromethane with no evidence of co-crystallized solvent. Again, an antiperiplanar orientation of the 2-oxazolinyl moieties within the molecular structure ( Fig. 2) was found. In contrast to (1), a more distinct twisting of the planes N1/C7/O1 and N2/C12/O2 compared to the plane B with interplanar angles of 16.16 (4) and 15.14 (4) , respectively, was found.

Figure 1
The asymmetric unit of (1), shown with 50% probability displacement ellipsoids. H atoms are drawn as green spheres of an arbitrary radius.

Figure 2
The asymmetric unit of (2), shown with displacement ellipsoids drawn at the 50% probability level. H atoms are drawn as green spheres of arbitrary radius.
Additionally, parallel-displacedstacking with Cg1Á Á ÁCg1 i = 3.5064 (12) Å (Cg1 denotes the centroid calculated for the arene atoms) and a horizontal displacement of I = 0.996 (2) Å (for a description of geometric parameters ofassociated arenes, see: Snyder et al., 2012) between the centroids was found. The interplanar distance is R = 3.3620 (13) Å . Theinteraction gives rise to antiperiplanar dimers linked to each other by an inversion. Features of intermolecular bonding for (1) are illustrated in Fig. 4.
The supramolecular contacts found for (2) are depicted in Fig. 5. A comparablestacking motif as for compound (1) was found within the crystal structure of (2) (Fig. 6). The centroid-centroid distance Cg1Á Á ÁCg1 i = 3.6142 (8) Å is slightly increased compared to (1). The interplanar distance is R = 3.2862 (9) Å with a remarkably increased horizontal centroid-centroid displacement of I = 1.5044 (15)   View along the a axis of the crystal packing of compound (1).
Other structures generally lack halide substitution at the central arene, although substitutional variety at the 4 0 -positions was found. Instead of 4,4-dimethyl substitution, derivatives bearing hydrogen atoms (LAFNEM; Chen et al., 2004), hydroxymethyl (MODQIH; Javadi et al., 2014) or isopropyl groups (DOWGOM; Mei et al., 2009) have been found. For those structures, no features of intermolecularinteractions could be observed. Instead, C-HÁ Á Á interaction becomes obvious for LAFNEM and DOWGOM. It is supposed that halide substitution increases dispersion interaction at modest horizontal centroid-centroid separations (Arnstein & Sherrill, 2008), thus promotingstacking for (1) and (2). As a result of the presence of electronegative atoms, hydrogen bonding and van der Waals contacts can also be found for the structures mentioned.
Langer et al. found the same C8 T C9 conformation (with respect to the numbering scheme used herein) within the 2-oxazoline ring of 2-(4-hydroxyphenyl)-4,4-dimethyl-2oxazoline (CELMAI; Langer et al., 2006) as for the 2-oxazoline moieties in (1) and (2). Conformational analysis of the 2-oxazolines within the structures discussed herein showed that all possible conformations twisted around C8-C9 can be found, that are C8 T C9 (two times within DOWGOM, CELMAI) and C9 T C8 (LAWCAO, ROHMIL). Folding into an envelope conformation was only observed at C8 with examples for C8 E (two times within DOWGOM, ROHMIL) and E C8 (FILNAQ, two times within ROHMIL) conformations. This might suggest that folding happens preferentially at the less-substituted methylene position. Planar conformations have been found for MODQIH, LAFNEM, and FILNAQ.

Refinement
Crystal data, data collection, and structure refinement details are summarized in Table 3. Primary atom site locations were assigned with EDMA (Palatinus et al., 2012) from electron densities obtained by SUPERFLIP (Palatinus & Chapuis, 2007). The remaining secondary non-carbon atom sites were located from the difference Fourier map. All non-hydrogen atoms were refined with anisotropic displacement parameters.
Full-matrix least-squares refinement on F 2 was done with SHELXL2014/7 (Sheldrick, 2008). Carbon-bound hydrogen atoms were positioned geometrically and refined riding on their respective carbon atom. Bond lengths were fixed at 0.95 Å (aromatic H), 0.98 Å (methyl H), and 0.99 Å (methylene H). U iso (H) was fixed at 1.5 U eq (O) and U eq (C) for hydroxyl and methyl hydrogens or 1.2 U eq (C) for the remaining hydrogens. Methyl hydrogens were fitted to the experimental electron density by allowing them to rotate around the C-C bond with a fixed angle (HFIX 137).  The synthesis scheme of (1) and (2), starting from 1-bromo-3,5dicyanobenzene. The numbering scheme for the title compounds is given.
For (1), occupancy refinement of O3 gave an occupancy of 0.15543 (611) which was subsequently fixed at 0.15. The hydrogen atoms H3A and H3B were located with the help of CALC-OH, which is the WinGX (Farrugia, 2012) implementation of Nardelli's method (Nardelli, 1999) of OH atom positioning. The coordinates of those hydrogen atoms were refined freely while applying restraints to the overall water geometry (O-H = 0.84 Å and HÁ Á ÁH = 1.328 Å ).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. ( (2) 3,5-Bis(4,4-dimethyl-1,3-oxazolin-2-yl)-1-iodobenzene Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. All nonhydrogen atoms were refined with anisotropic displacement parameters. Carbon-bound hydrogen atoms were positioned geometrically and refined riding on their respective carbon atom. Bond lengths were fixed at 0.95 Å (aromatic H), 0.98 Å (methyl H), and 0.99 Å (methylene H). U iso (H) was fixed at 1.5 U eq (O) and U eq (C) for hydroxyl and methyl H atoms or 1.2 U eq (C) for the remaining H atoms. Methyl H atoms were fitted to the experimental electron density by allowing them to rotate around the C-C bond with a fixed angle (HFIX 137).