Substitution of ligands in dichloro-{2-(arylazo)heterocycle}palladium(II) by 8-quinolinol: kinetics and mechanistic studies

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Nucleophilic substitutions of Pd(N,N′)Cl2[(N,N′ = 1-methyl-2-(arylazo)imidazole (RaaiMe), p-RC6H4N=NC3H2NN-1-Me; 2-(arylazo)pyridine (Raap), p-RC6H4N=NC5H4N; 2-(arylazo)pyrimidine (Raapm), p-RC6H4N=NC4H3N2 where R = H (a), Me (b), Cl (c)] with 8-quinolinol (HQ) have been examined by spectrophotometry at 298 K in MeCN solution. The product, Pd(Q)2, has also been confirmed by independent synthesis from Na2[PdCl4] and HQ in EtOH. The kinetics of the reaction have been studied under pseudo-first-order conditions and the analyses support a nucleophilic association path. A single phase reaction has been observed and follows the rate law, rate = a + k [Pd(N,N′)Cl2] [HQ]2. Thus, the reaction is first order in [Pd(N,N′)Cl2] and second order in [HQ]. External addition of Cl−(LiCl) suppresses the rate. The rate increases as follows: Pd(RaaiMe)Cl2 < Pd(Raap)Cl2 < Pd(Raapm)Cl2.

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