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Fluorinated ligands play an important role in bilogical activity [i, ii]. Especially those containing trifluoromethyl groups, play an important role in medicines and agrochemicals [iii, iv].

In recent years, we have developed general synthesis of 1,3,5-substituted pyrazole derived ligands, and focussed the research on the development of methods for regioselective synthesis [v]. In particular, we have synthesized N-alkyl-3-pyridine-5-trifluoromethylpyrazole derived ligands substituted with different groups in N1 position. With these ligands we report the reaction front Pd(II). The reaction of the ligands with [PdCl₂(CH₃CN)₂] gives complexes [PdCl₂(L)] (Figure 1). The stoichiometries of all complexes are independent of the M:L molar ratio. These complexes were characterized by elemental analyses, spectroscopic techniques, mass spectrometry, and X-ray diffraction methods. The metal atom of each structure is surrounded by an identical core composed by one L coordinated via one pyrazole nitrogen and one pyridine nitrogen, finishing the coordination of the metal with two chlorine ligands in cis disposition (Figure 2). The spectroscopic techniques are IR, ¹H NMR, ¹³C{¹H} NMR and ¹⁹F{¹H} NMR. The ¹⁹F{¹H} NMR spectra show a signal between -60.2 and -61-7 ppm, for the CF₃ group, comparable to those found for other complexes described in the literature [vi].

Treatment of [PdCl₂(L)] with pyridine (py) and NaBF₄ or triphenylphosphine (PPh₃) and AgBF₄ yielded [Pd(L)(py)₂](BF₄)₂ and [Pd(L)(PPh₃)₂](BF₄)₂, respectively (Figure 1). The ¹H NMR and ¹³C{¹H} NMR spectra of both complexes show that the two monodentate ligands coordinated to Pd (py, PPh₃) are non-equivalent, and two signals can be observed.

The ³¹P{¹H} NMR spectra for [Pd(L)(PPh₃)₂](BF₄)₂ complexes consist of broad doublet signals with chemical shifts in the usual range for Pd(II) complexes (36.1-33.9 ppm), indicating that both PPh₃ groups are non-equivalent.

Finally, the reaction of the complex [PdCl₂(L⁴)] (L⁴ = 2-(3-pyridin-2-yl-5-trifluoromethylpyrazol-1-yl)ethanol) with 1 mol of AgBF₄ in CH₂Cl₂ yields [PdCl₂(L⁴)](BF₄). In this complex the ligand acts as tridentate, coordinated to Pd(II) by Npyrazole, Namino and Oalcohol finishing the coordination of the metal with one chlorine ligand.

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ii R. Filler, Y. Kabayashi, Biomedical Aspects of Fluorine Chemistry, Kodansha Ltd, Tokyo, Japan, 1982, p. 246.
iii C. Heidelberger, N.K. Chaudhuri, P. Danneberg, D. Mooren, L. Giesbachl, R. Duschinsky, R.J. Schnitzer, E. Pleven, J. Scheiner, Nature 179 (1957) 663.
iv A.V. Fokin, A.F. Kolomiyets, J. Fluorine Chem. 40 (1988) 247.
v V. Montoya, J. Pons, V. Branchadell, J. Ros, Tetrahedron 61 (2005) 12377.
vi S.P. Singh, D. Kumar, B.G. Jones, M.D. Threadgill, J. Fluorine Chem. 94 (1999) 199.