Novel water soluble palladium(II) complexes featuring tetrazolylacetic acids and their esters

Abstract

2-R-2H-Tetrazol-5-ylacetic acids (R=iso-Pr, tert-Bu, CH2COOH) (1a–c) react with PdCl2 in 5% (w/w) MeOH in 1M HCl furnishing the palladium(II) water soluble complexes trans-[PdCl2L2] (2a–c). In the presence of EtOH in the reaction mixture, esterification of the tetrazolylacetoxy groups occurs leading to trans-[PdCl2(ethyl 2-R-2H-tetrazol-5-ylacetate)2] (3a–c). In the case of reaction of 2-tert-butyl-tetrazol-5-ylacetic acid 1b with PdCl2 increasing of the proportion of methanol up to 50% (w/w) led to the esterification to give trans-[PdCl2(methyl 2-tert-butyl-tetrazol-5-ylacetate)2] 4b. Complexation of isomeric 5-methyl-1H-tetrazol-1-ylacetic acid 5 with PdCl2 at the same conditions leads to trans-[PdCl2(5-methyl-1H-tetrazol-1-ylacetic acid)2] 6 and trans-[PdCl2(ethyl 2-(5-methyl-1H-tetrazol-1-yl)acetate)2] 7. The complexes obtained were characterized by HRESI+-MS, 1H, 13C{1H} NMR, and IR spectroscopies as well as by X-ray diffraction (for 2a, 3a, 3b, 4b and 6·H2O). According DSC/TG analysis the thermal decomposition of the complexes occurs by the same mechanism similar to that of the free ligands. In all cases it starts with evolution of molecular nitrogen from the tetrazole ligand which is accompanied by an exothermic effect.