Nucleophilic displacement of halides from monocationic platinum(II) complexes containing neutral tridentate chelating ligands with sulfur and nitrogen donors: kinetics and equilibria

Abstract

Kinetic and equilibrium measurements on the displacement of halides from the substrates [Pt(L)X]⁺[L = diethylenetriamine, 2,6-bis(methylsulfanylmethyl)pyridine, bis(2-pyridylmethyl) sulfide or 2,2′ :6′,2″-terpyridine, X = Cl, Br or l] with the nucleophiles Cl^–, Br^– and l^– have been carried out in methanol at 25 °C and constant ionic strength. The results are discussed in terms of the relative stability of the planar ground and five-co-ordinate transition states. The significant differences in kinetic behaviour along the series are related to the presence of π-interacting pyridine rings as well as to the nature of the donor atoms trans and cis to the replaceable halogen. The equilibrium parameters, the leaving-group effect and the intimate mechanism are also discussed and compared with literature data.