Reactions of the dirhenium(II) complexes Re2X4(mu-dppm)(2) (X = Cl, Br; dppm = Ph2PCH2PPh2) with isocyanides. 21.(1) A comparison with the complexes Re2Cl4(mu-dppE)(2) and Re2Cl4(mu-dcpm)(2) (dppE = Ph2PC(=CH2)PPh2; dcpm = Cy2PCH2PCy2) and the structural characterization of complexes of the types Re2Cl4(mu-LL)(2)(CNR), Re2Cl4(mu-LL)(2)(CNR)(2), and [Re2Cl3(mu-LL)(2)(CNR)(3)](+) (LL = dppm, dppE, dcpm; R = t-Bu, Xyl)

A study of the reactions between the triply bonded dirhenium(II) complexes Re2Cl4(mu-LL)(2), where LL = Ph-2-PCH2PPh2 (dppm), Ph2PC(=CH2)PPh2 (dppE), or Cy2PCH2PCy2 (dcpm), with the isocyanides t-BuNC and XyINC (Xyl = 2,6-dim ethylphenyl) show that complexes of the type Re2C4(mu-LL)(2)(CNR), Re2Cl4(m u-LL)(2)(CNR)(2), and [Re2Cl3(mu-LL)(2)(CNR)(3)](+) are formed sequentially . Several of these have been structurally characterized by X-ray crystallog raphy: Re2Cl4(mu-dppm)(2)(CNXyl) (2), Re2Cl4(mu-dcpm)(2)(CNXyl) (11), Re2Cl 4(mu-dppE)(2)(CN-t-Bu)(2) (6), Re2Cl4(mu-dcpm)(2)(CN-r-BU)(2) (12), and [Re 2Cl3(mu-dpFE)(2)(CN-t-Bu)(3)]Cl (7). Complex 2 has an A-frame-like structur e with a single mu-Cl bridging ligand, whereas for 11 the structure is like that of 2 but without this bridge, viz., Cl2Re(mu-dppm)(2)ReCl2(CNXyl) wit h a Re-Cl bond approximately collinear with Re drop Re. The symmetrical com plexes 6 and 12 are essentially isostructural and have an anti-arrangement of the two t-BuNC ligands. Complex 7 has the open bioctahedral structure [( t-BuNC)(2)ClRe(mu-dppE)(2)ReCl2(CN-t-Bu)](+), which is quite different from that of the edge-sharing bioctahedron found in salts of the [Re2Cl3(mu-dpp m)(2)(CNXyl)(3)](+) cation and its neutral congener Re2Cl3(mu-dppm)(2)(CNXy l)(3); preliminary crystallographic data for the latter compound show the s tructure to be (XyINC)ClRe(mu-Cl)(mu-CNXyl)(mu-dppm)(2)ReCl(CNXyl) with an all-cis arrangement of XyINC ligands. The Re-Re bond distances of 2, 6, 7, 11, and 12 occur in the range 2.289-2.380 Angstrom and are consistent in al l instances with the retention of a Re drop Re bond, albeit weakened by som e degree of Re-->CNR(pi*) back-bonding.