Mixed carbonyl–nitrile complexes of dirhenium(II). The structural characterization and reactivity of salts of the [Re2Cl3(μ-dppm)2(CO)(NCMe)n]+ cations (dppm=Ph2PCH2PPh2, n=1 or 2)

The monocarbonyl complexes Re2X4(μ-dppm)2(CO) (X=Cl or Br) react with stoichiometric quantities of the nitriles RCN (R=Me or Ph) in the presence of TlY (Y=PF6 or O3SCF3) to afford complexes of the type [Re2X3(μ-dppm)2(CO)(NCR)]Y and [Re2X3(μ-dppm)2(CO)(NCR)2]Y in high yield. Crystal structure determinations on the salts [Re2Cl3(μ-dppm)2(CO)(NCMe)]O3SCF3 and [Re2Cl3(μ-dppm)2(CO)(NCMe)2]ReO4 have shown that the former has the unsymmetrical structure [(MeCN)(CO)ClRe(μ-dppm)2ReCl2]+ with a ReRe bond (ReRe distance 2.2881(7) Å), while the bis-nitrile complex is the edge-sharing bioctahedron [(MeCN)ClRe(μ-Cl)(μ-CO)(μ-dppm)2ReCl(NCMe)]+, with an all-cis arrangement of the μ-CO and two MeCN ligands and a ReRe bond (ReRe distance 2.5669(4) Å). The species [Re2X3(μ-dppm)2(CO)(NCMe)]+ and [Re2X3(μ-dppm)2(CO)(NCMe)2]+ readily interconvert upon the addition or loss of an acetonitrile ligand and, along with their benzonitrile analogues, they react with halide, XylNC and acetylene to afford Re2X4(μ-dppm)2(CO), [Re2X3(μ-dppm)2(CO)(CNXyl)2]Y and [Re2X3(μ-dppm)2(CO)(η2-C2H2)]Y, respectively.