4-[(Z)-Allylamino(phenyl)methylene]-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one

The title compound, C20H19N3O, exists in a keto–enamine tautomeric form. The pyrazolone ring makes dihedral angles of 20.52 (10) and 77.73 (5)° with the two phenyl rings and an intramolecular N—H⋯O hydrogen bond occurs. A weak intermolecular C—H⋯O hydrogen bond is observed in the crystal structure. The allyl group is disordered over two positions, with site-occupancy factors of 0.533 (5) and 0.467 (5).

The title compound, C 20 H 19 N 3 O, exists in a keto-enamine tautomeric form. The pyrazolone ring makes dihedral angles of 20.52 (10) and 77.73 (5) with the two phenyl rings and an intramolecular N-HÁ Á ÁO hydrogen bond occurs. A weak intermolecular C-HÁ Á ÁO hydrogen bond is observed in the crystal structure. The allyl group is disordered over two positions, with site-occupancy factors of 0.533 (5) and 0.467 (5).
The structure of (I) is shown in Fig. 1. The dihedral angles formed by the pyrazolone ring with the two phenyl rings C5-C10 and C12-C17 are 20.52 (10) and 77.73 (5)°, respectively. The O atom of the 3-methyl-1-phenylpyrazol-5-one moiety and the N atom of the allylamino group are available for coordination with metals. The pyrazole ring is planar and atoms O1, C1, C2, C11 and N3 are almost coplanar, the largest deviation being 0.0195 (11) Å for atom C11. The dihedral angle between this mean plane and the pyrazoline ring of PMBP is 2.01 (12)°. The bond lengths within this part of the molecule lie between classical single-and double-bond lengths, indicating extensive conjugation. A strong intramolecular N3-H3···O1 hydrogen bond (Table 1) is observed, leading to a keto-enamine form. The crystal structure includes intermolecular C-H···O hydrogen bonds (Table 1 and Fig. 2).

Experimental
Compound (I) was synthesized by refluxing a mixture of 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (10 mmol) and allylamine (10 mmol) in ethanol (80 ml) over a steam bath for about 10 h. Excess solvent was removed by evaporation and the solution was cooled to room temperature. After 4 d, a colorless solid was obtained and this was dried in air. The product was recrystallized from ethanol, to afford colorless crystals of (I) suitable for X-ray analysis.

Refinement
C-bound H atoms were positioned geometrically, with C-H = 0.95-0.96 Å and were refined as riding, with U iso (H) = 1.2U eq (C). The amine H atom (H3) found in a difference map was refined freely. The allyl group shows positional disorder.
supplementary materials sup-2 Figures Fig. 1. View of the title compound, with displacement ellipsoids drawn at the 50% probability level.

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 > σ(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 Occ. (