A Trans-Spanning Diphosphine Ligand Based on a <i>m</i><i>-</i>Terphenyl Scaffold and Its Palladium and Nickel Complexes

The new diphosphine ligand 2,6-bis(2-((diphenylphosphino)methyl)phenyl)benzene (1) has been prepared for potential use as a terdentate pincer-type ligand. Upon examination of the coordination chemistry with representative palladium and nickel centers, however, it was discovered that it acts as a bidentate trans-spanning ligand upon coordination to form trans-[(1)PdCl2] (2) and trans-[(1)NiCl2] (3). Attempts to promote CH activation of the central benzene ring and produce a terdentate pincer binding mode for 1 were unsuccessful. Reaction of 2 and [Li(OEt2)][B(C6F5)4] led to formation of the dicationic bis(chloro)-bridged dimer [(1)2{Pd2(μ2-Cl)2}][B(C6F5)4]2 (4), in which two ligands 1 have rearranged to span across the dichlorodipalladium core. The structures of air- and moisture-stable 2−4 were confirmed by X-ray crystallography.