A versatile diphosphine ligand: cis and trans chelation or bridging, with self association through hydrogen bonding

The diphosphine ligand, N,N'-bis(2-diphenylphosphinoethyl)isophthalamide, dpipa, contains two amide groups and can form cis or trans chelate complexes or cis,cis or trans,trans bridged complexes. The amide groups are likely to be involved in intramolecular or intermolecular hydrogen bonding. This combination of properties of the ligand dpipa leads to very unusual structural properties of its complexes, which often exist as mixtures of monomers and dimers in solution. In the complex [Au2(μ-dpipa)2]Cl2, the ligands adopt the trans,trans bridging mode, with linear gold(I) centers, and the amide groups hydrogen bond to the chloride anions. In [Pt2Cl4(μ-dpipa)2], the ligands adopt the cis,cis bridging mode, with square planar platinum(II) centers, and the amide groups form intermolecular hydrogen bonds to the chloride ligands to form a supramolecular one-dimensional polymer. Both the monomeric and dimeric complexes [PtMe2(dpipa)] and [Pt2Me4(μ-dpipa)2] have cis-PtMe2 units with cis chelating or cis,cis bridging dpipa ligands respectively; each forms a supramolecular dimer through hydrogen bonding between amide groups and each contains an unusual NH···Pt interaction. An attempted oxidative addition reaction with methyl iodide gave the complex [PtIMe(dpipa)], which contains trans chelating dpipa, while a reaction with bromine gave a disordered complex with approximate composition [Pt2Me3Br5(μ-dpipa)2], which contains trans,trans bridging dpipa ligands.