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.

双膦配体N,N′-双(2-二苯基膦乙基)间苯二甲酰胺（dpipa）含有两个酰胺基团，可形成顺式或反式螯合配合物，以及顺,顺或反,反式桥联配合物。该配体的酰胺基团易参与分子内或分子间氢键作用。

dpipa的上述特性使其配合物具备极不寻常的结构特征：这类配合物在溶液中通常以单体与二聚体的混合物形式存在。

在配合物[Au₂(μ-dpipa)₂]Cl₂中，配体采取反,反式桥联模式，金(I)中心呈线性配位构型，酰胺基团与氯离子形成氢键。在配合物[Pt₂Cl₄(μ-dpipa)₂]中，配体采取顺,顺式桥联模式，铂(II)中心呈平面四配位构型，酰胺基团通过与氯配体形成分子间氢键，构筑得到超分子一维聚合物。

单核配合物[PtMe₂(dpipa)]与双核配合物[Pt₂Me₄(μ-dpipa)₂]均含有顺式PtMe₂结构单元，分别对应顺式螯合dpipa配体与顺,顺式桥联dpipa配体；二者均通过酰胺基团间的氢键作用形成超分子二聚体，且均存在罕见的NH···Pt相互作用。

尝试与碘甲烷进行氧化加成反应，得到配合物[PtIMe(dpipa)]，其中dpipa采取反式螯合配位模式；而与溴的反应则得到组成为近似[Pt₂Me₃Br₅(μ-dpipa)₂]的无序配合物，其中dpipa配体采取反,反式桥联配位模式。