Kinetics and mechanism of reaction of α-picolinic acid with dichloro-{2-(arylazo)- heterocycle}palladium(II) complexes

Abstract

Abstract The reaction between Pd(N,N')Cl2 [(N,N'= l-methyl-2-(arylazo)imidazole (RaaiMe), p-RC6H4- N=N-C3H2NN-1 -Me; 2-(arylazo)pyridine (Raap), p-C6H4-N=N-C5H4N; 2- (arylazo)pyrimidine (Raapm), p-C6H4-N=N-C4H3N2; where R=H (a), Me (b), CI (c)] and apicolinic acid (α-picH) have been examined spectrophotometrically in MeCN solution at 298K. The product is Pd(a-pic)2 which has been supported by pure compound synthesis from Na2[PdCl4] and α-picH. The kinetics of the nucleophilic substitution reaction has been studied under pseudo-first-order condition. The reaction proceeds in a biphasic manner. The kinetic analysis confirms the nucleophilic association path. External addition of CI- (LiCl) suppresses the rate. On considering the consecutive reaction A-> B-> C the rate data have been evaluated. Each phase shows first-order dependence on [α-picH]. Rate-1 = {a1+k1[(α-picH]}[ Pd(N,N')Cl2]; rate-2 = {a1+k2[(α-picH]}[Pd(N,N')Cl2], with the k1 (first phase rate constant) > k2 (second phase rate constant). Increase in π-acidity of the ligand N,N' increases the rate and follows the order: Pd(RaaiMe)Cl2 < Pd(Raap)Cl2 < Pd(Raapm)Cl2 .