2-(3-Methoxyphenyl)-1,3-dihydro-1,3,2-benzodiazaborole

The title compound, C13H13BN2O, is one in a series of 1,3,2-benzodiazaboroles featuring a 2-methoxyphenyl substitution at the 2-position in the nitrogen–boron heterocyle. The dihedral angle between the mean planes of the benzodiazaborole and 2-methoxyphenyl ring systems is 21.5 (1)°. There is an intermolecular hydrogen bond between one of the NH groups and the methoxy O atom. This hydrogen bond leads to an infinite hydrogen-bonded chain colinear with the a axis.

The title compound, C 13 H 13 BN 2 O, is one in a series of 1,3,2benzodiazaboroles featuring a 2-methoxyphenyl substitution at the 2-position in the nitrogen-boron heterocyle. The dihedral angle between the mean planes of the benzodiazaborole and 2-methoxyphenyl ring systems is 21.5 (1) . There is an intermolecular hydrogen bond between one of the NH groups and the methoxy O atom. This hydrogen bond leads to an infinite hydrogen-bonded chain colinear with the a axis.
Unlike most triarylborane compounds which require dimesitylborolyl moieties for the enhancement of their stability, 2arylbenzo-1,3,2-diazaborole compounds have been reported to be water and air stable without any additional dimesityl groups (Weber et al., 2009). To gain insight into the intriguing characteristics exhibited by these compounds, we (Sithebe et al., 2011) and other researchers (Maruyama et al., 2002 andWeber et al. 2011) have directed our reseach focus towards the investigation of the photophysical studies as well as the determination of the crystal structures of 1,3,2-benzodiazaborolyl compounds.
The molecule features a 1,3,2-benzodiazaborolyl backbone with a five-membered diazaborole ring substituted with hydrogen atoms at the 1-and 3-positions, and a 3-methoxyphenyl ring at the 2-position. The 1,3,2-benzodiazaborolyl backbone of the molecule is essentially planar, however, the 3-methoxyphenyl ring at the 2-position, is rotated out of plane with a dihedral angle of 21.5 (1)°. The two N-B bonds are approximately equal (averaged to 1.433 (2) Å). The N1 -B-N2 bond angle is 105.2 (1)°, the N1-B-C1 and N2-B-C1 bond angles are slighly different, measuring 125.4 (1)° and 129.3 (1)°, respectively (refer to Figure 1 for the atom numbering scheme). These bond lengths and angles compare favourably to those of previously reported diazaborolyl systems (Weber et al., 2009). The molecules are linked through hydrogen bonding forming infinite, one-dimensional chains co-linear with the a-axis (Figure 2). The amine NH acts as the hydrogen bond donor and the etheryl oxygen atom the H-bond acceptor. The hydrogen bond lengths and bond angles are summarized in Table 1.
Experimental 3-Methoxyphenylboronic acid (1.00 g, 5.18 mmol) and o-phenylenediamine (0.56 g, 5.18 mmol) were dissolved in toluene (80 ml) in a two neck flask equipped with a Dean and Stark Apparatus, magnetic stirrer bar and reflux condenser.
The mixture was heated under reflux overnight and the solvent was removed in vacuo, affording 2-{3-methoxyphenyl}benzo-1,3,2-diazaborole as an off-white solid. The desired product was purified using a flash column and radial chromatography using Hexane: Ethyl acetate (8:2) as the eluent. Crystals suitable for X-ray difraction were grown by slow evaporation of a n-hexane:dicloromethane (6:4) solution.

Refinement
All non-hydrogen atoms were located in the difference Fourier map and refined anisotropically. and U iso = 1.2 U eq , and C-H(methyl) distances of 0.96 Å and U iso = 1.5 U eq . The amine hydrogen atoms were located in the difference Fourier map and allowed to refine isotropically. In the absence of significant anomalous scattering, Friedel pairs were merged.

Figure 1
Displacement ellipsoid plot of (1) at the 50% probability level.    Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H atoms treated by a mixture of independent and constrained refinement w = 1/[σ 2 (F o 2 ) + (0.0725P) 2 ] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.32 e Å −3 Δρ min = −0.20 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.058 (6) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 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.