Dinuclear palladium(I) complexes with isocyanide and N-donor bidentate ligands

Abstract

Reactions of the dinuclear palladium(I) complex [Pd₂Cl₂(RNC)₄](R = 2,4,6-Me₃C₆H₂)1 with the N-donor compounds 2,2′-bipyridyl (bipy), 1,10-phenanthroline (phen), and 2,9-dimethyl-1,10-phenanthroline (dmphen) gave dipalladium(I) complexes with chelating N-donor ligands, [Pd₂(RNC)₂L₂][PF₆]₂(L = bipy 2, phen 3 or dmphen 4). The structures of 2 and 4 were characterized by X-ray crystallography. The cation of 2 is composed of two Pd atoms joined by a σ bond [2.518(3)Å] each of which has a square-planar co-ordination involving a terminal isocyanide and a chelating bipy ligand. Complex 3 is expected to have a structure similar to 2 on the basis of spectroscopic data. Complex 4 exhibits a distorted dinuclear structure due to the steric bulk of the N-donor ligand. The Pd–Pd bond length is 2.599(2)Å. Each dmphen ligand chelates to a Pd atom and the isocyanide acts as semibridging ligand. The similar reactions of complex 1 with 2,2′-biquinoline (bquin) and 1,8-naphthyridine (napy) afforded the isocyanide-bridged dipalladium(I) complexes, [Pd₂(µ-RNC)₂(bquin)₂][PF₆]₂5 and [Pd₂(µ-NRC)₂(napy)₄][PF₆]₂6, in 24–36% yields. Complex 6 comprises a dinuclear palladium(I) core bridged by two isocyanide ligands [Pd–Pd 2.747(4)Å] with four terminal napy ligands co-ordinated in a monodentate fashion.