Interaction of adenine with dichloro-[1-alkyl-2-(naphthylazo)-imidazole]palladium(II) complexes: kinetic and mechanistic studies

Interaction of adenine (A) with dichloro-1-alkyl-2-(α-naphthylazo)imidazole] palladium(II) Pd(α-NaiR)Cl₂], 1 and dichloro-1-alkyl-2-(β-naphthylazo)imidazole] palladium(II) Pd(β-NaiR)Cl₂], 2 {where R=Me (a), Et (b) or Bz (c)} in MeCN-water (50% v/v) medium to yield {1-alkyl-2-(α-naphthylazo)imidazole}(adenine)]palladium(II) perchlorates (3a, 3b, 3c) and {1-alkyl-2-(β-naphthylazo)imidazole}(adenine)]palladium(II) perchlorates (4a, 4b, 4c) was studied. The products were characterized by physico-chemical and spectroscopic methods. The reaction kinetics were second order overall, being first order in both the Pd(II) complex and adenine. The effect of adding chloride was consistent with rate-limiting dissociation of chloride from the complex. Thermodynamic parameters were determined from temperature variation experiments. The second-order rate constant k ₂ corroborates with the experimental Δ^‡H° values, while the negative values of Δ^‡S° indicate that the reaction proceeds through an associative inner sphere mechanism.