Diethyl [(4-nitrobenzamido)(phenyl)methyl]phosphonate

In the title compound, C18H21N2O6P, the dihedral angle between the benzene and phenyl rings is 85.1 (2)°. In the crystal, molecules are linked via pairs of N—H⋯O(=P) hydrogen bonds, forming inversion dimers with graph-set notation R 2 2(10). One of the ethyl groups is disordered over two sets of sites, with occupancies 0.746 (11) and 0.254 (11).

In the title compound, C 18 H 21 N 2 O 6 P, the dihedral angle between the benzene and phenyl rings is 85.1 (2) . In the crystal, molecules are linked via pairs of N-HÁ Á ÁO( P) hydrogen bonds, forming inversion dimers with graph-set notation R 2 2 (10). One of the ethyl groups is disordered over two sets of sites, with occupancies 0.746 (11) and 0.254 (11).

Comment
The title compound (I) was synthesized for a study of its antimicrobial activity against Bacillus subtilis. This aminophosphonate derivative was found to have weak antimicrobial activity (inhibition zone = 7 mm). The molecular structure of the title compound is shown in Fig. 1. The dihedral angle between the benzene (C2-C7) ring and phenyl (C9-C14) ring is 85.1 (2)°. In the crystal, molecules are linked via pairs of N-H···O(═P) hydrogen bonds forming inversion dimers with with graph-set notation R 2 2 (10) (Bernstein et al., 1995). One of the ethyl groups (C17/C18) is disordered over two sets of sites with occupancies 0.746 (11) and 0.254 (11). Bond lenths and angles in (I) are in agreement with the values reported for a similar structure (Fang et al., 2004).

Experimental
The hydrochloride of diethyl amino(phenyl)methylphosphonate was prepared according to the literature procedure (Takahashi et al., 1994). This ester (1.08 g, 5 mmol) was dissolved in dry tetrahydrofuran (20 ml) to which triethylamine (0.7 ml) was added, and the solution was added dropwise to 4-nitrobenzoyl chloride (0.9 g, 5 mmol) in the same solvent (10 ml) (see Fig. 1). After completion of the reaction, the precipitate was separated and the filtrate was extracted with ethyl acetate, dried over anhydrous MgSO 4 and concentrated under vacuum. The residual liquid was purified by column chromatography to give the title compound. Single crystals suitable for X-ray analysis were obtained by slow evaporation of a petroleum ether -ethyl acetate solution (3:1 v/v) of the title compound.

Refinement
The H atoms were positioned geometrically (C-H = 0.93-0.98 Å) and were included in the refinement in the ridingmodel approximation with U iso (H) = 1.2U eq (C) or 1.5U eq (C methyl ). The H atom bonded to the N atom was refined independently with U iso (H) = 1.2U eq (N).

Figure 1
The reaction scheme.  The molecular structure of the title compound with displacement ellipsoids drawn at the 30% probability level. H atoms are drawn as spheres of arbitrary radii and the open bonds indicate the minor component of disorder.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > 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 Occ. (