Synthesis and structure of highly substituted pyrazole ligands and their complexes with platinum(II) and palladium(II) metal ions

Reaction of 3-methoxycarbonyl-2-methyl- or 3-dimethoxyphosphoryl-2-methyl-substituted 4-oxo-4H-chromones 1 with N-methylhydrazine resulted in the formation of isomeric, highly substituted pyrazoles 4 (major products) and 5 (minor products). Intramolecular transesterification of 4 and 5 under basic conditions led, respectively, to tricyclic derivatives 7 and 8. The structures of pyrazoles 4a (dimethyl 2-methyl-4-oxo-4H-chromen-3-yl-phosphonate) and 4b (methyl 4-oxo-2-methyl-4H-chromene-3-carboxylate) were confirmed by X-ray crystallography. Pyrazoles 4a and 4b were used as ligands (L) in the formation of ML2Cl2 complexes with platinum(II) or palladium(II) metal ions (M). Potassium tetrachloroplatinate(II), used as the metal ion reagent, gave both trans-[Pt(4a)(2)Cl-2] and cis[Pt(4a)(2)Cl-2], complexes with ligand 4a, and only cis-[Pt(4b)(2)Cl-2] isomer with ligand 4b. Palladium complexes were obtained by the reaction of bis(benzonitrile)dichloropalladium(II) with the test ligands. trans-[Pd(4a)(2)Cl-2] and trans- [Pd(4b)(2)Cl-2] were the exclusive products of these reactions. The structures of all the complexes were confirmed by IR, H-1 NMR and FAB MS spectral analysis, elemental analysis and Kurnakov tests. (C) 2004 Elsevier Ltd. All rights reserved.