3-tert-Butyl-1-(3-nitrophenyl)-1H-pyrazol-5-amine

In the title compound, C13H16N4O2, the pyrazole ring forms a dihedral angle of 50.61 (6)° with the 3-nitro-phenyl ring. The plane of the nitro group is twisted by 6.8 (7)° out of the plane of the phenyl ring. In the crystal, the molecules are linked by N—H⋯N and N—H⋯O hydrogen bonds, forming sheets in the bc plane. In addition, a weak C—H⋯N interaction is observed.

In the title compound, C 13 H 16 N 4 O 2 , the pyrazole ring forms a dihedral angle of 50.61 (6) with the 3-nitro-phenyl ring. The plane of the nitro group is twisted by 6.8 (7) out of the plane of the phenyl ring. In the crystal, the molecules are linked by N-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonds, forming sheets in the bc plane. In addition, a weak C-HÁ Á ÁN interaction is observed.

Cabrera-Ortiz Comment
The recent past has evidenced an ever-increasing interest in pyrazole based ligands. The interest in such compounds is due, first of all, to their variety of coordination complexes with a great number of metal ions and, second, to their ability to provide an extensive variety of coordination geometries and significant structural nuclearity when introducing different kinds of heteroatoms (Ahmed et al. 2005;Schutznerová et al. 2012). The past few years have seen considerable rise in interest in the design of various pyrazole-based ligands for particular metal binding site (Guerrero et al. 2009).
As a part of our current research work focused on the development of new bioactive heterocyclic compounds and continuing with the use of pyrazolic Schiff bases (Quiroga et al., 2008;Abonia et al. 2002Abonia et al. , 2004Abonia et al. , 2010, in the synthesis of pyrazolopyrimidines, we want to describe the compound 5-amino-3-tert-butyl-1-(3-nitro-phenyl)-1H-pyrazole (I), which is a structural isomer of a related compound previously reported by Low (Low et al., 2004).
The structure of the title compound is shown in Figure 1. The compound consists of a ring pyrazole substituted by 3nitro-phenyl ring bonded to N1, amino group in C5 and tertbutyl group in C3. The pyrazole and phenyl rings are not coplanar, they are forming a dihedral angle of 50.61 (6)°. The nitro group is rotated around C14-N3 bond by 6.8 (3)°.
These angle values are larger than those described for the isomeric compound 5-amino-3-tertbutyl-1-(4-nitro-phenyl)-1Hpyrazole (Low et al., 2004). In the crystal, the molecules are linked by N-H-N and N-H-O intermolecular hydrogen bonds forming sheets in the bc plane. In additon, a weak intermolecular C-H···N interaction is observed ( Figure 2, Table   1).

Experimental
To a solution of conc hydrochloric acid (3.8 ml) in water (33 ml), 3-nitrophenylhydrazine (1.5001 g, 9.87 mmol) and 4,4dimethyl-3-oxopentanenitrile (1.8502 g, 14.80 mmol) were added. The mixture was heated at 70 °C for 1 h. Then, conc hydrochloric acid (3.8 ml) was added and the mixture was heated for 1 h more. After cooling, crushed ice was added and neutralized with conc ammonium hydroxide. The resulting solid was filtered under reduced pressure, washed with cold water (3 X 5 ml) and dried at ambient temperature affording the title compound (I) as a yellow solid [ N 21.52%, found C 60.36; H 6.42; N 21.88%. Crystals of the title compound suitable for single-crystal X-ray diffraction were grown by slow diffusion of pentane into a CH 2 Cl 2 solution of the title compound.

Refinement
The positional parameters of the amino H atom were refined with a distance restraint of 0.90 (1)Å while those of the other H atoms were calculated geometrically (C-H = 0.93-0.98 Å). All H atoms were refined with U iso (H) = 1.2U eq of the parent atom.

Figure 1
Structure of (I), with the numbering scheme. The displacement ellipsoids are drawn to 40% of probability.  The crystal packing of (I), only the H atoms involved in intermolecular interaction were drawn.

Special details
Geometry. All e.s.d.'s (except the those 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.