Nickel(II), palladium(II), and platinum(II) complexes containing cis- or trans-1,2-bis(diphenylphosphino)ethene: isomorphous crystal structures in the cyanide case

Abstract

Mono- and binuclear NiII, PdII, and PtII complexes of cis- or trans-1,2-bis(diphenylphosphino)ethene (cis- or trans-dppen) have been prepared and characterized by X-ray diffraction methods, 19;Pt 1H and 31P 1H NMR spectroscopy, FAB mass spectrometry, IR spectroscopy, elemental analyses and melting points. The X-ray structures of some rare examples of cis-dicyanide complexes of the type [M(CN)2(cis-dppen)] (MNi (1), MPd (2), MPt (3)) are given for the first time. All three crystal lattices are isomorphous and allow comparison of the radii of Ni, Pd, and Pt atoms. In 1–3 the coordination is square planar. In all cases the ethene bridges are nearly coplanar with the coordination planes, which can be explained by π-bonding interactions. Due to the isomorphous crystal lattices, 1–3 show analogous shortest intermolecular repulsive C–H···M contact approaches leading to small deviations from coplanarity.The removal of one coordinated chloride in [NiCl2(cis-dppen)] by AgBF4 followed by subsequent treatment with bis(diphenylphosphino)amine, NH(PPh2)2 (dppam), leads to the novel complex [NiCl(cis-dppen) (dppam)](BF4) (4). However, the analogous abstraction of both chlorides in [MCl2(cis-dppen)] (MPd, Pt) and reaction with dppam produces [M(cis-dppen)(dppam)](BF4)2 (MPd (5), MPt (6)). In the case of trans-dppen, the reaction with Pd(CN)2 leads to another novel cis-dicyanide complex of the type [Pd2(CN)4(μ-trans-dppen)2] (7). Substitution of chloride in [Pt2Cl4(μ-trans-dppen)2] by cyanide leads to the analogous PtII compound [Pt2(CN)4(μ-trans-dppen)2] (8). It is believed, that the unsaturated nature of cis- or trans-dppen leading to π-bonding interactions with the metal-ligand bonds, is responsible for the unusual stability of cis-dicyanide complexes. For dppam the presence of electronic delocalization is well-known. These effects are discussed in view of the X-ray structures of 1–3 and related compounds.