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

The monocarbonyl complexes Re2X4(mu-dppm)(2)(CO) (X = Cl or Pr) react with stoichiometric quantities of the nitriles RCN (R = Me or Ph) in the presenc e of TlY (Y = PF6 or O3SCF3) to afford complexes of the type [Re2X3(mu-dppm )(2)(CO)(NCR)]Y and [Re2X3(mu-dppm)(2)(Co)(NCR)(2)]Y in high yield. Crystal structure determinations on the salts [Re2Cl3(mu-dppm)(2)(CO)(NCMe)]O3SCF3 and [Re2Cl3(mu-dppm)(2)(CO)(NCMe)(2)]ReO4 have shown that the former has t he unsymmetrical structure [(MeCN)(CO)ClRe(mu-dppm)(2)ReCl2](+) C with a Re drop Re bond (Re-Re distance 2.2881(7) Angstrom), while the bis-nitrile co mplex is the edge-sharing bioctahedron [(MeCN)ClRe(mu-Cl)(mu-CO)(mu-dppm),R eCl(NCMe)](+), with an all-cis arrangement of the mu-CO and two MeCN ligand s and a Re=Re bond (Re-Re distance 2.5669(4) Angstrom. The species [Re2X3(m u-dppm)(2)(CO)(NCMe)](+) and [Re2X3(mu-dppm)(2)(CO)(NCMe)(2)](+) readily in terconvert upon the addition or loss of an acetonitrile ligand and, along w ith their benzonitrile analogues, they react with halide, XylNC and acetyle ne to afford Re2X4(mu-dppm)(2)(CO), [Re2X3(mu-dppm)(2)(CO)(CNXyl)(2)]Y and [Re2X3(mu-dppm)(2)(CO)(eta(2)-C2H2)]Y, respectively. (C) 2000 Elsevier Scie nce S.A. All rights reserved.