Diethyl 2-[phenyl(pyrazol-1-yl)methyl]propanedioate

There are two independent molecules in the asymmetric unit of the title compound, C17H20N2O4, which differ slightly in the orientation of the phenyl ring and carbonyl groups with respect to the pyrazole unit. In the first molecule, the dihedral angle between the phenyl and pyrazole rings is 68.99 (13)° while the two carbonyl groups make a dihedral angle of 72.1 (4)°. The corresponding values in the second molecule are 68.54 (14) and 71.5 (4)°, respectively.

There are two independent molecules in the asymmetric unit of the title compound, C 17 H 20 N 2 O 4 , which differ slightly in the orientation of the phenyl ring and carbonyl groups with respect to the pyrazole unit. In the first molecule, the dihedral angle between the phenyl and pyrazole rings is 68.99 (13) while the two carbonyl groups make a dihedral angle of 72.1 (4) . The corresponding values in the second molecule are 68.54 (14) and 71.5 (4) , respectively.
Therefore several bimetallic metal complexes, in many cases exploring the well-known polydentate ligands, appear in this scenario as the most promising concept to employ in either enzyme / drug interaction or electron transfer process, in the last case involving biological oxygen transfer (Sechi et al., 2009b;Ramkumar et al., 2008). Another exciting example of the application of such polydentate ligands involves the synergic water activation, that occurs via the so-called remote metallic atoms. Such organometallic compounds are expected to promote or block the H-I activity [Zeng et al. (2008b)]. The examples given above clearly demonstrate that polydentate ligands are of special interest in the field of bioorganometallic chemistry [Patil et al. (2007)].
The structure of the title compound was established by 1 H and 13 C NMR and confirmed by its elemental analyses and single-crystal X-ray structure. Crystals of the title compound contain two molecules in the asymmetric unit. The difference between the molecules lies in the orientation of the phenyl and pyrazol rings and carbonyl planes in each molecule as shown in the fitting drawing (Fig. 2). Thus in the first molecule (C11 to C143) the dihedral angles between the phenyl and pyrazol rings is 68.99 (13)° and between the two carbonyl groups is 72.1 (4)°. Whereas in the second molecule (C21 to C243), equivalent angles have as values 68.54 (14)° and 71.5 (4)°, respectively. The conformational difference between the independent molecules, as shown in Fig. 2, can also be described by torsion angles: N11-C11···C131-C132 = 79.71 (15), C11-C12···O11O12 = 46.54 (9) and C11-C12···O13-O14 = 47.02 (9) in the first molecule. In the second molecule, the corresponding values are 54.31 (14), 41.77 (9) and 47.44 (9), respectively. The bond lengths and angles in the title compound ( Fig. 1) are found to have normal values [Allen et al., 1987].

Experimental
To a solution of diethyl benzylpropanedioate (5 mmol) in water (25 ml) was added 1H-pyrazol (6 mmol) in the presence of acetic acid (0.1% mol). The mixture was stirred continuously at room temperature until the starting material was completely consumed. After removing the solvent, the crude products were dissolved in diethyl ether (2 x 40 ml) and washed with water until the pH became neutral. The organic solvent was dried with sodium sulphate and then evaporated. The residue was purified by recrystallization from a mixture ether/hexane (1:1) to give a white solid in 74% yield. R f = 0.45 (ether/hexane: All H atoms were fixed geometrically and treated as riding with C-H = 0.95 Å (aromatic), 0.99 Å (methylene), 0.98 Å (methyl) and 1.00 Å (methine) with Uiso(H) = 1.2Ueq (aromatic, methine, methylene) and Uiso(H) = 1.5Ueq (methyl). Fig. 1. Molecular structure of the title compound with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.  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.

Figures
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 > 2sigma(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.