2,4-Bis(dimethylamino)-1,3,5-trimethyl-6-(nitrooxy)borazine

In the title compound, C7H21B3N6O3, the r.m.s. deviation of the borazine ring atoms is 0.019 Å. The dimethylamino groups are orientated at 41.80 (7) and 36.43 (7)° with respect to the borazine ring. The nitrooxy group is almost normal to the borazine ring [dihedral angle = 85.33 (14)°]. The methyl C atom trans to the NO3 group is displaced by −0.512 (3) Å from the ring plane, whereas the two ortho-methyl C atoms are displaced by 0.239 (3) and 0.178 (3) Å.

Sandia is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94 A L85000.

Comment
The 2,4-bis(dimethylamino)-6-nitrooxy-1,3,5-trimethylborazine (I) is a buff-colored solid that has not been previously reported. Figure 1 shows the molecule for this compound as an atomic displacement ellipsoid plot. Bond lengths for the dimethylamine (DMA) ligands, B-N, N-O, and B-O bonds are consistent with expected values. This molecule is very similar to that the previously reported 2,4-Bis(dimethylamino)-6-chloro-1,3,5-trimethylborazine (II); see Rodriguez and Borek, (2013). The difference is merely the exchange of Cl in (II) for a nitrooxy group shown here in (I). The steric nature of the DMA ligands and their proximity to methyl groups bound to the nitrogen atoms of the borazine ring appears to create conditions in the molecule that drive these borazine-bound methyl groups away from the plane created by the borazine ring. Figure 2 shows the molecule of (I) bisected by the plane defined by the borazine ring; the plane is extended through the bound ligands. The view in Figure 2 shows how the C3 methyl, bracketed by the rotated DMA molecules, is displaced upward, out-of-the-plane of the borazine ring (in terms of the molecule orientation in the figure) by an angle of 20.9 (1)°. Likewise, C1 and C2 methyls are displaced downward from the borazine plane by tilt angles of 8.80 (9)° and 7.24 (9)°, respectively. The rotation of the DMA ligands from the borazine plane generates dihedral angles of 41.80 (7)° and 36.43 (7)° for the B2/N4/C4/C5 and B3/N5/C6/C7 DMA groups, respectively. The counter-rotation of the two DMA ligands relative to the C3 methyl is the likely steric mechanism to displace the C3 methyl at a much larger angle compared to the C1 and C2 methyl groups (which are each bracketed by a DMA and the nitrooxy group). The plane defined by the nitrooxy group is nearly perpendicular to the borazine ring, having a dihedral angle of 85.0 (1)° as shown in Figure 2. The O2 and O3 O atoms are terminal and no detection of H atoms was observed in the difference-fourier maps. The molecule is charge balanced as shown. Figure 3 shows the packing arrangement of the two molecules of (I) within the triclinic unit cell. Additional molecules extending beyond the defined cell are also shown so as to give the viewer a sense of the packing arrangement as it extends in space. Observation of Figure 3 with an eye for symmetry reveals the inversion center present in the unit cell, generating the two formula units per cell (Z=2). Based on the absence of any clearly defined donor-acceptor pairs within the structure, there did not appear to be strong hydrogen-bonding interactions within this structure. This was supported by software tests (HTAB) that also indicated the absence of any donor-acceptor pairs. Careful visual inspection of the packing of (I) molecules indicated that the positioning of the terminal O atoms (O2 and O3) were such that they pointed toward H atoms of neighboring methyl groups. Therefore, some weak C-H···O interactions are likely present. However, the distances between the nitrooxy O atoms and neighboring protons exceeded 2.6 Å for C-H···O interactions and the estimated C-H···O bond angles were atypical of hydrogen bonds. Therefore, the packing appears to be dictated by Van der Waals interactions coupled with perhaps weak nitrooxy-methyl interactions. Experimental Compound (I) was obtained using a modification of the published procedure of Brennan, et al. (1960). One equivalent of 2,4-Bis(dimethylamino)-6-chloro-1,3,5-trimethylborazine was reacted with one equivalent of silver nitrate in acetonitrile.
After stirring the reaction mixture, the solution was filtered to remove precipitated silver chloride, and the solvent was removed using vacuum techniques. This product was then recrystallized from anhydrous hexanes, and then was vacuum distilled (bp 114-116°C at 800 mTorr). The liquid distillate slowly crystallized upon standing at room temperature resulting in a buff-colored solid with a melting point of 68 to 72°C. Crystals formed in this manner were of sufficient quality for single-crystal structure analysis. The product purity was determined by nuclear magnetic resonance (1H, 11B, 13C).  The molecular structure of (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms.  View of molecule (I) with superimposed borazine plane to illustrate devaitions of methyl, dimethylamine, and nitrooxy ligands from the borazine plane. H atoms have been removed for clarity. See text for details.

Figure 3
Packing diagram for (I) showing relative orientation of molecules in unit cell. H atoms have been removed for clarity. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq B1 0.4283 (