Mixed Carbonyl-Isocyanide and Carbonyl-Nitrile Complexes Derived from the Reactions of the Multiply Bonded Dirhenium(II) Complexes Re2X4(dppm)2(CO) (X=Cl or Br; dppm=Ph2PCH2PPh2). The Structural Characterization of Cl2Re(μ-dppm)2ReCl(CO) and Cl2Re(μ-Cl)(μ-CO)(μ-dppm)2ReCl(CNxylyl)

Article abstract of DOI:10.1021/ja00276a023

Reactions of the triply bonded dirhenium(II) complexes Re2X4(dppm)2 (X=Cl or Br; dppm=bis(diphenylphosphino)methane) with carbon monoxide yielded the monocarbonyls X2Re(μ-X)(μ-dppm)2ReX(CO).The chloride derivative Re2Cl4(dppm)2(CO) (1), which has been characterized by X-ray diffraction, cocrystallizes with three independent benzene molecules in the hexagonal space group P6₃/m (No. 176).The cell dimensions are a=28.469(4) Angstroem, c=14.301(2) Angstroem, V=10037(4) Angstroem³, and Z=6.The Re-Re bond distance is 2.338(1) Angstroem and the molecule has a novel A-frame-like structure.The crystal structure was refined to R=0.048 (unit weights).Reactions of this molecule with 1 equiv of an isocyanide (RNC) generate complexes of stoichiometry Re2Cl4(dppm)2(CO)(CNR) (R=i-Pr, t-Bu, xylyl, or mesityl) in which the CO ligand is in either a terminal or bridging position, depending on the isocyanide used.The xylylNC derivative Cl2Re(μ-Cl)(μ-CO)(μ-dppm)2ReCl(CNxylyl) (2) has been characterized by X-ray crystallography.Compound 2 crystallizes in the monoclinic system, space group P2₁/n, with a=18.211(4) Angstroem, b=15.907(2) Angstroem, c=20.887(6) Angstroem, β=93.63(3) deg, V=6048(1) Angstroem³, and Z=4.The crystal structure was refined to residuals of R=0.0650, R_w=0.0691.The Re-Re bond distance is 2.581(2) Angstroem, and the molecule comprises a pair of distorted, edge-sharing octahedra.The monocarbonyl reacts readily with an excess of nitrile R'CN in the presence of TlPF6 to yielded the PF6^- salts of stoichiometry PF6 (R'=CH3, C2H5, or C6H5).The IR and NMR (1H and 31P<1H>) spectral properties of these particular complexes suggest that there is an all-cis arrangement of chloride ligands on one side of the molecule.