Nucleophilic discrimination and the trans effect. The kinetics of displacement of X from trans-[Pt(L)(X)Cl2]n–(L = Me2SO, Et2S, PMe3, PEt3, PPh3, or AsEt3; X = Cl, n= 1; X = MeOH, n= 0) by neutral and anionic nucleophiles

Abstract

The kinetics of the reaction trans-[Pt(L)(X)Cl₂]^n–+ L′→trans-[Pt(L)(L′)Cl₂]^n′–+ X (X = Cl^–, n= 1, L = Me₂SO, Et₂S, PMe₃, PEt₃, PPh₃, or AsEt₃, L′= pyridine (py), Me₂S, Et₂S, PPh₃, Me₂SO, thiourea (tu), or NNN′N′-tetramethylthiourea (tmtu), n′= 0; L′= Cl^–, Br^–, I^–, or SCN^–, n′= 1; X = MeOH, n= 0, L′= Cl^–, Br^–, I^–, or SCN^–, n′= 1) have been studied in 95% methanol + 5% water at 25 °C. The second-order rate constants, k₂, for the anionic substrates do not follow the usual dependence upon n⁰_Pt′ the anionic nucleophiles being much less reactive than predicted. A new nucleophilicity scale, based on [Pt(Et₃As)Cl₃]^– as standard substrate, does give linear relationships for all the anionic substrates. The relationship between the nucleophilic discrimination and the nature of the trans ligand is discussed.