Mechanism of Silver-Promoted Ligand Metathesis in Square-Planar Complexes of d⁸ Ions. Kinetics of Formation and Molecular Structures of a Trinuclear Intermediate [(Me)(N−N)Pt(μ-Cl)Ag(μ-Cl)Pt(N−N)(Me)]⁺ and Its Dinuclear Evolution Product [(Me)(N−N)Pt(μ-Cl)Pt(N−N)(Me)]⁺ (N−N = ArNC(Me)C(Me)NAr, Ar = 2,6-(<i>i</i>-Pr)₂C₆H₃)

Abstract

The silver-assisted ligand methatesis reaction involving a platinum(II) complex of formula [PtClMe(N,N-chelate)] with acetonitrile has been investigated. By using a suitably hindered N,N-chelate, an otherwise hardly detectable trinuclear species has been isolated and characterized through X-ray diffractometry. The trinuclear cation consists of two nearly orthogonal [PtCl(Me)(N,N-chelate)] square-planar units entrapping an Ag+ cation through the chloride ligands that, acting as bidentate, form a linear AgCl2 unit with two nonequivalent Ag−Cl bonds. The residual acidity of the silver cation is satisfied by one secondary Ag−Pt interaction [Ag−Pt(1) = 2.82 Å] in which the platinum atom acts as a donor. Kinetic studies have demonstrated that the silver assistance operates both through a simple associative step and through a pathway in which the above trinuclear complex is an active intermediate. In a noncoordinating solvent the latter species evolves with AgCl loss and formation of a dinuclear Pt,Pt complex showing a rare single chloride bridge