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-Pr)2C6H3)

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 Angstrom] 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.