Crystal Structure of N,N-bis-(3-Carbomethoxy-5-methyl-pyrazol-1-ylmethyl)aniline

The tripodal ligand N,N-bis-(3-carbomethoxy-5-methylpyrazol-1-yl)methyl aniline (2) has been prepared by the condensation of aniline with two equivalents of N-hydroxymethyl[3-carbomethoxy-5-methyl]pyrazole. The molecule consists of two structurally analogous 3-carbomethoxy-5-methylpyrazol-1-ylmethyl moieties, which adopt a transoidal conformation via a central aniline ring, suggesting that this tripodal ligand is highly flexible and could accommodate many metals by coordination.


Introduction
Polydentate pyrazole compounds are known and are particularly interesting as promising ligands for the building of polynuclear complexes as models for bioinorganic systems [1], as well as for the discovery of new catalyst precursors [2]. We are currently working on the synthesis and coordination of monotripodal nitrogen ligands, such as N,N-bis-[(3,5-dimethyl-1-pyrazolyl)methyl]alkylamines [3], to gain insight into the coordination behaviour of larger ligand systems containing both nitrogens of the pyrazolyl groups as potential N-donor atoms, and a delocalised π-conjugated spacer such as an aryldiamine. This research effort is directed towards the preparation of new mixed-valence transition metal complexes for catalysis, and the study of electronic communication [4,5]. The X-ray structure of the N,N-bis-(3-carbomethoxy-5-methylpyrazol-1-ylmethyl) aniline (2) was determined to establish its spatial conformation in the free state before coordination to metals.

Results and Discussion
Synthesis of the tripodal ligand 2.

Crystallographic study of tripodal ligand 2
The X-ray data for the crystal of the title molecule were collected using graphite-monochromatized Mo Kα radiation at 298 K. The structure was solved by direct methods and refined by full-matrix leastsquares with an anisotropic temperature factor for the non-hydrogen atoms. The hydrogen atoms are localised on the difference Fourier map and adjusted to 0.97 Å to bonded atoms. The molecular structure of the title compound is shown in Scheme 2, together with the atomic labelling scheme.
The molecule consists of two 3-carbomethoxy-5-methylpyrazol-1-ylmethyl moieties, which are structurally analogous, and which adopt a transoidal conformation via a central aniline ring suggesting that this tripodal ligand is highly flexible and could accommodate many metals for coordination.
Interestingly molecule 2 has one pseudo C 2 symmetry axis which is formed by the phenyl ring and amine nitrogen centres (N1-C15-C18), so each pyrazole ring is the symmetrical counterpart of the other one. The same observation can be made for the rest of molecule 2 (for example C1 and C2). The electrostatic spatial intermolecular repulsion between N4 and N5 is probably responsible of this general transoidal disposition. These data led us to note the basic character of N4 and N5. Scheme 2: Molecular structure of the title compound with atom labelling.
Thermal ellipsoids are drawn at the 50% probability level.
The N5-C8 bond length is 1.335(5) Å, suggesting that the 3-carbomethoxy-5-methylpyrazole group of compound 2 is less conjugated. This could be due to the electronic attraction of the CO 2 CH 3 group. The same observation is valid for the N=N bonds; for example the N2=N4 bond length is 1.353(4) Å. The refinement of the structure has been realized using suitable crystallography programs [11][12][13][14]. Table 1 summarises the crystal and experimental data. Selected bond distances and bond angles are listed in Tables 3 and 4, respectively.

Conclusions
We report the easy synthesis of tridentate pyrazolic derivative ligands to establish the structure of one tripodal ligand of this class. We are now investigating whether this mono-tripodal class could display some biological activity and we are extending this synthesis to some bis-tripodal class compounds which are suitable bridging ligands as models of molecular wires.

Acknowledgements
Part of the costs of this research was met by the "Programme Thématique d'Appui à la Recherche Scientifique PROTARS N° P1T2/27" Grant from the Ministry of National Education of Morocco, the "Wylaya d'Oujda", to which the authors' thanks are due.

General
The NMR spectrum was recorded for a CDCl 3 solution on a Bruker AM 200 spectrometer working at 200.13 MHz. The chemical shifts are reported in δ values. The melting point was measured on an Electrothermal apparatus and is uncorrected. Reagents and solvents were purchased from commercial suppliers.