Two acyclic imides: 3-bromo-N-(3-bromobenzoyl)-N-(pyridin-2-yl)benzamide and 3-bromo-N-(3-bromobenzoyl)-N-(pyrimidin-2-yl)benzamide

The title acyclic meta-bromo substituted imide derivatives were synthesized in good yields from condensation reactions of 3-bromobenzoyl chloride with 2-aminopyridine or 2-aminopyrimidine using standard condensation reaction conditions and subsequent column chromatography.


Chemical context
Acyclic imide chemistry, as RCON(R 0 )COR, (where R,R 0 are aryl or alkyl groups) has developed over the past 130 years from condensation reactions of benzoyl chlorides with aminoaromatics such as 2-aminopyridines or 2-aminopyrimidines (Marckwald, 1894;Tschitschibabin & Bylinkin, 1922;Huntress & Walter, 1948). From these reactions, a mixture of the benzamide and acyclic imide is usually obtained, with the relative yields of each component dependent on the starting materials and reaction conditions. The imides can also be synthesized directly from a benzamide starting material. The presence of an ortho-N in the benzamide heteroaromatic ring is an important feature needed to obtain the imide derivative in good yields (Mocilac et al., 2010(Mocilac et al., , 2012Khavasi & Tehrani, 2013).
In recent research on macrocyclic imides, we and others have noted the role of the imide hinge in the development of macrocyclic imides (Evans & Gale, 2004;Mocilac & Gallagher, 2013). Both syn and anti types of acyclic imide conformation have been observed in the macrocycles. It has been noted how this affects the formation of both trezimide and tennimide macrocycles and with the syn conformation essential for trezimide formation (Mocilac & Gallagher, 2013). Further studies are needed to demonstrate the ease with which the two distinct conformations can interconvert in acyclic imides.

Structural commentary
From the condensation reaction of meta-BrC 6 H 4 COCl with 2-aminopyridine and 2-aminopyrimidine, the benzamide and imide products were obtained and separated by standard column chromatography for each reaction. Using 2-aminopyridine, Brmo and Brmod, (I) were obtained and for 2aminopyrimidine, Brmopz and Brmopzd, (II) were isolated. Brmo and Brmopz are the (1:1) benzamide products, whereas Brmod, (I) and Brmopzd, (II) are the (2:1) acyclic imides. Both (I) and (II) (Figs. 1-2) adopt similar molecular structures to the majority of published structures (Groom et al., 2016;Gallagher et al., 2009a,b) but they differ in their supramolecular features . Both molecules lack strong donor groups (no amide group as in the benzamides; Donnelly et al., 2008) but have strong acceptors such as O C and Nheteroaromatic rings that are able to participate in many weaker intermolecular interactions in their crystal structures, not to mention potential -ring aromatic stacking and C-HÁ Á Á interactions (Martinez & Iverson, 2012;Nishio, 2004).
A comparison of acyclic imides and their key torsion angles demonstrates the range of angles observed and the key differences between the syn (carbonyl OÁ Á ÁO separations of $4.5 Å ) and anti conformations (OÁ Á ÁO separations of $3.7 Å ) in crystal structures (Groom et al., 2016). In (I) the O1Á Á ÁO2 distance is 3.871 (3) Å and the O1 C1Á Á ÁC2 O2 torsion angle is À109.3 (5) compared to an O1Á Á ÁO2 = 3.646 (5) Å distance and an O1-C1Á Á ÁC2 O2 torsion angle of À96.6 (5) in (II). We have also previously used the cisoid and transoid terminology for the disposition of the two C O groups; this is used to describe the orientation and direction of the C O groups/aromatic rings with respect to one another (Mocilac et al., 2018).

Supramolecular features
The prevalent anti-conformation imide structural type is demonstrated in the structures of both (I) and (II) and is similar to the molecular structures of the ortho-F (SOLSUI) and meta-F (DOKXOR) imide structures (Gallagher et al., 2009a,b), the chloro-and methyl-imides (Mocilac et al., 2018) and two benzene relatives (Shukla et al., 2018). This contrasts with the syn type as observed in the crystal structure of Mood, a 2-methylbenzoyl imide (Mocilac et al., 2018)   An ORTEP view of (II) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.

Figure 1
An ORTEP view of (I) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. (Gallagher et al., 2009a,b) and N-benzene rings in the SEYSUN-type structures (Shukla et al., 2018).

Figure 3
A schematic diagram of the hydrogen-and halogen-bonding interactions in the crystal structure of (I).

Figure 4
A schematic diagram of the main intermolecular interactions in the crystal structure of (II).

Database survey
A literature search for acyclic imides provides several 2-aminopyridine structures of which DOKXOR a meta-F benzene derivative (Gallagher et al., 2009a) and CIJPET a meta-Cl derivative (Mocilac et al., 2018), are similar to (I) and (II). MEYYUK, an N-anthracene-9-carboxamide derivative (Kohmoto et al., 2001) and MOCTUT or N,N-dibenzoyl-4chloroaniline structures (Usman et al., 2002) are also similar in structure and conformation. Shukla and co-workers have detailed six halogenated N-benzoyl-N-phenylbenzamides (imides) that adopt both syn and anti conformations in the solid state (Shukla et al., 2018). The reason why they adopt either conformation is not obvious and suggests that a transformation between either conformation as having a low activation energy barrier. Such imide behaviour (in adopting either of the syn or anti structures) has been known for decades although there does not seem to have been much investigation into possible fluxional behaviour and various influences driving towards one particular conformation or other. The intermolecular interactions in (I) (C19 H12 Br2 N2 O2 0 a) with displacement ellipsoids at the 30% level.    For both structures, data collection: CrysAlis PRO (Rigaku OD, 2015); cell refinement: CrysAlis PRO (Rigaku OD, 2015); data reduction: CrysAlis PRO (Rigaku OD, 2015); program(s) used to solve structure: SHELXT14/7 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL14/7 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2020); software used to prepare material for publication: SHELXL14/7 (Sheldrick, 2015b).

Special details
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq

3-Bromo-N-(3-bromobenzoyl)-N-(pyrimidin-2-yl)benzamide (Brmopzd)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.89 e Å −3 Δρ min = −0.67 e Å −3 Special details 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.