Dinuclear palladium(ii) complexes with bridging amidate ligands

Abstract

New homonuclear dimeric Pd(II) complexes have been synthesized by the reaction of Pd(en)²⁺ or Pd(bipy)²⁺ (where en = ethylenediamine and bipy = 2,2′-bipyridine) units with acetamide or by the Pd(II) mediated hydrolysis of CH₃CN. In these dimers the two metal centers are bridged by either two amidates or by the combination of one hydroxo group and one amidate ligand. The crystal structures of complexes {[Pd(bipy)]₂(µ-1,3-CH₃CONH)₂}(NO₃)₂·H₂O·1/2(CH₃)₂CO·1/2CH₃CN (3) and {[Pd(bipy)]₂(µ-1,3-CH₃CONH)₂}(OTf)₂ (4) showed intrametallic Pd–Pd distances of 2.8480(8) Å (3) and 2.8384(7) Å (4), respectively, in accordance with the accepted values for a strong Pd–Pd interaction. The presence of π⋯π interactions between the bipyridine ligands on the di-µ-amidate complexes of Pd(bipy)²⁺ shortens the distance between the two Pd centers and allows the formation of the metal–metal interaction. By contrast, the crystal structure of complex {[Pd(en)]₂(µ-1,3-CH₃CONH)₂}(OTf)₂·H₂O (6), (where OTf = triflate) where there is no π⋯π interaction between the ligands on the metal centers, is also reported, and no Pd–Pd interaction is observed. Additionally, one of the complexes, {[Pd(en)]₂(µ-OH)(µ-CH₃CONH)}(NO₃)₂ (5), presents an interesting hydrogen bonded 3-D network formed by nitrate ions and water molecules. All complexes have been characterized by infrared and ¹H NMR spectroscopy.