Kinetics and mechanism of complex formation of 3-(2-thiazolylazo)-2,6-diaminopyridine with palladium(II)

The kinetics of complex formation of 3-(2-thiazolylazo)-2,6-diaminopyridine (TADAP) with palladium(II) was studied. The observed reaction rate constants with respect to palladium and TADAP were determined, and true second-order reaction rate constants corresponding to the formation of [PdH3L](3+) and [PdH2L](2+), in 15 associated solvents with a spatial structure and to the formation of PdL in 26 aprotic nonstructured and nonassociated solvents were calculated. Different variants of nucleophilic substitution in palladium(II) complexes were considered, and, based on this consideration, the rate constants of substitution (direct or with participation of a solvent molecule) of a TADAP molecule for the leaving group were calculated. The relationship between these rate constants and the dielectric constant, as well as the polarizability of molecules (molecular refraction of a medium), was established. The mechanisms of complex formation of palladium(II) with TADAP in associated and nonassociated solvents were proposed.