2-(4-Chlorophenyl)naphtho[1,8-de][1,3,2]diazaborinane

The title compound, C16H12BClN2, is one in a series of diazaborinanes, derived from 1,8-diaminonaphthalene, featuring substitution at the 1, 2 and 3 positions in the nitrogen-boron heterocycle. The structure deviates from planarity, the torsion angle subtended by the p-chlorophenyl ring relative to the nitrogen–boron heterocycle being −44-.3(3)°. The molecules form infinite chains with strong interactions between the vacant pz orbital of the B atom and the π-system of an adjacent molecule. The distance between the B atom and the 10-atom centroid of an adjacent naphthalene ring is 3.381 (4) Å. One N-H H atom is weakly hydrogen bonded to the Cl atom of an adjacent molecule. This combination of intermolecular interactions leads to the formation of an infinite two-dimensional network perpendicular to the c axis.


Comment
The structure of the title compound is nominally planar with a slight rotation of the p-chlorophenyl ring relative to the naphthalene rings and boron-nitrogen heterocycle. The N1-B-C11-C12 torsion angle is -4.3 (3)° (refer to Figure 1 for the atom numbering scheme). The orientation of the heterocycle relative to the diazaborolyl groups is critical, since as the rings approach co-planarity there is more effective overlap of the π-systems of the boron atom and the carbon atom to which it is attached. The bond lengths N1-B and N2-B are approximately equal, measuring 1.416 (3) and 1.405 (3) Å, respectively, while the B-C11 bond length is 1.568 (4) Å. The Cl-C14 bond length is 1.736 (2) Å. The N1-B-N2 bond angle is 115.6 (2)°, the N1-B-C11 and N2-B-C11 bond angles are equal, both measuring 122.2 (2)°. These bond length and angles are comparable to those of previously reported diazaborolyl systems (Weber et al., 2009).
Examination of the title compound showed that there is a short contact between the boron atom and the naphthalene rings of an adjacent molecule. The distance from the boron atom to the 10-atom naphthalene centroid is 3.381 (4) Å. These B-π interaction link the molecules, forming infinite, one-dimensional chains. Adjacent one dimensional chains are then weakly hydrogen-bonded together by a N-H hydrogen atom and the chlorine atom of the adjacent molecule. These hydrogen bonds are likely to be very weak as they are only nominally shorter than the sum of the van der Waals radii (0.022 Å shorter) ( Table   1). The combination of intermolecular interactions results in the formation of infinite, two-dimensional sheets ( Figure 2).
The two-dimensional sheet runs perpendicular to the c axis.

Experimental
To a solution of 1,8-diaminonaphthalene in toluene (4.11 mmol in 50 ml, 0.82M) (Letsinger & Hamilton, 1958;Slabber, 2011) was added the 3-chlorophenylboronic acid (4.11 mmol) in one portion. The round-bottomed flask was equipped with a Dean and Stark trap, and the solution was stirred and heated to reflux for 3 h. The solvent was removed in vacuo and column chromatography of the crude solid using silica gel as the stationary phase and eluting with CH 2 Cl 2 yielded pale green crystalline material upon evaporation of the eluent with a yield of 66%. Recrystallization of the material from dichloromethane yielded crystals suitable for single-crystal X-ray diffraction analysis were grown.

Refinement
The positions of all hydrogen atoms were calculated using the standard riding model of SHELXL97. with C-H(aromatic) distances of 0.93 Å and U iso = 1.2 U eq . The only exception is the NH hydrogen atoms which were located in the difference Fourier map and allowed to refine isotropically.

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.
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 > 2σ(F 2 ) is used only for calculating Rfactors(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.

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