Kinetic and mechanistic studies on the Pd-Cl cleavage of dichloro- [1-alkyl-2-(naphthylazo)imidazole]palladium(II) complexes by 2,2′-bipyridine

Abstract

The interaction of 2,2′-bipyridine 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] complexes {where alkyl R′ = Me (a), Et (b) or Bz (c)} in acetonitrile medium to yield [{1-alkyl-2-(α-naphthylazo) imidazole} (bipyridine)] palladium(II)diperchlorate (3a, 3b, 3c) and [{1-alkyl-2-(β-naphthylazo) imidazole}(bipyridine)] palladium(II) diperchlorate (4a, 4b, 4c) was studied. The products were characterized by microanalytical data and spectroscopic techniques (FT-IR, UV–vis, and NMR). The nucleophilic substitution reaction shows a first-order dependence of rate on each of the Pd(II) complex and 2,2′-bipyridine. Addition of LiCl to the reaction decreases the rate of reaction and has proved the cleavage of Pd–Cl bond at the rate-determining step. Thermodynamic parameters standard enthalpy of activation (Δ‡H°), and standard entropy of activation (Δ‡S°) were determined. The second-order rate constant k2 corroborates with the experimental Δ‡H° values. The negative values of Δ‡S° indicate that the reaction proceeds through an associative inner sphere mechanism. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 130–140, 2011