Displacement of chelate ligands from four-co-ordinate complexes. Part IV. Reactions of (3-azapentane-1,5-diamine)- and (3-methyl-3-azapentane-1,5-diamine)-chlorogold(III) complexes

Abstract

The kinetics of nucleophilic displacement of the chelate ligands 3-azapentane-1,5-diamine(3NH-pd) and 3-methyl-3-azapentane-1,5-diamine (3NMe-pd) from the complexes [AuCl(N–N–N)]Cl₂(N–N–N = 3NH- or 3NMe-pd) have been studied in 5% water–methanol solution at 25 °C. Under the experimental conditions used for the kinetic runs the predominant species in solution are [AuCl₂(HN–N–N)]²⁺ and [AuCl₃(H₂N–N–N)]²⁺ in which the polydentate ligand acts as bi- and uni-dentate. The observed rate equation in both cases is formally analogous to that found in displacement of NNN′N′-tetraethylethylenediamine (teen) and NNN′N′-tetramethylethylenediamine(tmen) from the complexes [AuCl₂(N–N)][ClO₄](N–N = teen or tmen) and is in accord with the mech-, [AuCl₂(HN–N–N)]²⁺ [graphic omitted] [AuCl₃(HN–N–N)]⁺ [graphic omitted] [AuCl₃(H₂N–N–N)]²⁺ [graphic omitted] [AuCl₄]^–+[H₃N–N–N]³⁺(i) anism in equation (i). From the kinetic data the values of K₁K₂ and k₃′ have been determined, and the, [AuCl(N–N–N)]²⁺ [graphic omitted] [AuCl₂(HN–N–N)]²⁺(ii) constant for equilibrium (ii) has been measured spectrophotometrically. The complex [AuCl(3NMe-pd)]²⁺ undergoes deprotonation of one of the two co-ordinated primary amine groups and the pK_a values, determined in 0.5 mol dm^–3 Na[ClO₄] and in 0.5 mol dm^–a NaCl, are reported.