SYNTHESIS AND X-RAY CRYSTAL-STRUCTURES OF DIMERIC NICKEL(0) AND TETRAMERIC COPPER(I) IODIDE COMPLEXES OF 2-DIPHENYLPHOSPHINO-3-METHYLPHOSPHININE

The dimer [Ni-2(mu-CO)(CO)(2)(mu-1)(2)] 2 has been prepared by two dif ferent procedures which involve the reaction of the 2-diphenyl-phosphi no-3-methylphosphinine ligand 1 with either Ni(COD)(2) or NiBr2 . DME/ Zn under CO atmosphere. The crystal structure of 2 has been determined by X-ray crystallography. As the analogous dppm complex, 2 adopts a W -frame structure with two bridging ligands 1, two terminal carbonyl li gands and one bridging carbonyl ligand. An electrochemical study revea ls that the electron density in the Ni-2 core is considerably reduced in 2 compared to the dppm complex. The reaction of 1 with two equivale nts of copper iodide yields the tetranuclear complex [Cu-4(mu-I)(2)(mu (4)-I)(2)(mu-1)(2)] 3 which has been identified by an X-ray diffractio n study. The structure of 3 consists of an octahedron having a square planar Cu-4 base bridged by two ligands 1 and two mu(2)-iodo atoms. Th e most surprising feature of this structure concerns the coordination of the two other iodide atoms respectively located at each apex of the octahedron, which display a face mu(4)-face-bridging bonding mode. (C ) 1997 Elsevier Science S.A.