Palladium(II) and platinum(II) complexes with polypyridylbenzene ligands

The ligands 1,3-bis(3-pyridyl)benzene (1), 1,3-bis(4-pyridyl)benzene (2) and 1,3,5-tris(4-pyridyl)benzene (3) have been prepared by Stille coupling of 3- or 4-trimethylstannylpyridine with the appropriate bromoarene. Ligands 1 and 2 react with [M(OTf)2(dppp)] (M=Pd, Pt) to produce the dipalladium- or diplatinum-containing macrocycles [M2(μ-1)2(dppp)2](OTf)4 or [M2(μ-2)2(dppp)2](OTf)4. These have been characterized by NMR spectroscopy and mass spectrometry and, in the case of [Pd2(μ-1)2(dppp)2](OTf)4, by X-ray crystallography. The molecular structure of the [Pd2(μ-1)2(dppp)2]4+ cation reveals a shallow arrangement of the aromatic rings, with the palladium atoms lying above and below. The tridentate ligand 3 reacts with [Pd(OTf)2(dppp)] to produce a trimetallic species of the form [Pd3(μ3-3)2(dppp)3](OTf)6.