The reactivity of 4′-substituted terpy platinum(II) complexes with bio-relevant azole nucleophiles. A kinetic and mechanistic study

Abstract

The rate of Chloride substitution from [Pt{(4′-ethylglycoxyl)-2,2′:6′,2″-terpyridine}Cl]Cl([PtCl(tpy)eg]Cl), [Pt{(4′-diethylglycoxyl)-2,2′:6′,2″-terpyridine}Cl]Cl([PtCl(tpy)deg]Cl) and [Pt{(4′-triethylglycoxyl)-2,2′:6′,2″-terpyridine}Cl]Cl([PtCl(tpy)teg]Cl), by a series of biological nitrogen donor nucleophiles, viz. pyrazole (Pz), triazole (Tz), imidazole (Im), 1-methylimidazole (MIm) and 1,2-dimethylimidazole (DIm) under pseudo first-order conditions as a function of concentration and temperature in methanol using UV/Visible spectrophotometry were investigated. The analysis of kinetic trend on the candidate complexes show that only the first carbon-oxygen pendant bond plays a crucial role in regulating the electron density donated by the polyethylenegycoxyl fragment. This is reflected in the insignificant change in the reactivity as the polyethyleneglycoxyl chain increases. The obtained kinetic data are supported by the DFT calculations that reveal a less electrophilic Pt(II) metal centre for complexes bearing the 4′-substituent. The temperature dependent studies support an associative mode of activation where bond formation in the transition state is favoured.