Pd2Ag triangle supported by two µ3-amidopyridine ligands

Abstract

[Pd(tmeda)(Hampy-N¹)(H₂O)]²⁺ (tmeda = N,N,N′,N′-tetramethylethylenediamine; Hampy = 2-aminopyridine) forms in the presence of Ag⁺ at pH 8–9 a triangular Pd₂Ag complex containing two deprotonated ampy⁻ ligands. It has been crystallized and structurally characterized with nitrate anions and a second co-crystallized AgNO₃, [{Pd(ampy)(tmeda)}₂Ag(µ-NO₃)₂Ag(NO₃)₂] (5). The two amidopyridine ligands are triply bridging, binding to Ag⁺ in a monodentate fashion viaN¹, and to two Pd^II centres in a µ₂-bridging fashion via the monodeprotonated N² position. The resulting four-membered Pd(ampy)₂Pd metallacycle is syn-planar with Pd⋯Pd separations of 3.0878(13) Å. The Pd⋯Ag distances are 3.0879(14) Å in 5 (isosceles triangle). In solution (D₂O), the two ampy⁻ ligand in 5 are non-equivalent as concluded from a detailed ¹H NMR spectroscopic study and confirmed by a ¹³C NMR spectrum. Removal of Ag⁺ from 5, as achieved by addition of Cl⁻, causes cluster degradation and linkage isomerization of Pd^II(tmeda) from the exocyclic N² to the endocyclic N¹ position.