Fast reactions at planar four-co-ordinate complexes. Part I. Nucleophilicity towards palladium(II) complexes

Abstract

Rates of nucleophilic substitution reactions (i)[L = PPrⁿ₃, AsEt₃, or piperidine, C₅H₁₁N; Y^–= Cl^–, N₃^–, Br^–, I^–, SCN^–, or (NH₂)₂CS] have been measured in methanol at 25 °C. A set of nucleophilic reactivity constants, trans-[PdL₂(NO₂)₂]+ Y^–→trans-[PdL₂(NO₂)Y]+ NO₂^–(i)n_Pd⁰= log (k₂[MeOH]/k₁), have been calculated, k₁ and k₂ referring to rate constants for the solvolytic path and for direct nucleophilic attack on the complex trans-[Pd(PPrⁿ₃)₂(NO₂)₂]. All the complexes studied obey the linear free-energy relation log k₂=sn_Pd⁰+ log k₁, where s is a nucleophilic discrimination factor. The n_Pd⁰ sequence resembles that already found for platinum(II) complexes.