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

摘要

Mono- and binuclear Ni-II, Pd-II, and Pt-II complexes of cis- or trans- 1,2-bis(diphenylphosphino)ethene (cis- or trans-dppen) have been prepared and characterized by X-ray diffraction methods, Pt-195 H-1 and P-31 H-1 NMR spectroscopy, FAB mass spectrometry, IR spectroscopy, elemental analyses and melting points. The Xray structures of some rare examples of cis-dicyanide complexes of the type [M(CN)(2)(cis-dppen)] (M=Ni (I), M=Pd (2), M=Pt (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 pi-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)] (M=Pd, Pt) and reaction with dppam produces [M(cis-dppen)(dppam)](BF4)(2) (M-pd (5), M=Pt (6)). In the case of trans dppen, the reaction with Pd(CN)(2) leads to another novel cis-dicyanide complex of the type [Pd-2(CN)(4)(mu-trans-dppen)(2)] (7). Substitution of chloride in [Pt2Cl4(mu-trans-dppen)(2)] by cyanide leads to the analogous Pt-II compound [Pt-2(CN)(4)(mu-trans-dppen)(2)] (8). It is believed, that the unsaturated nature of cis- or trans-dppen leading to pi-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. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 49]