Multiple Bonds between Main-Group Elements and Transition Metals. 86.1 Methyltrioxorhenium(VII) and Trioxo(η5-pentamethylcyclopentadienyl)rhenium(VII): Structures, Spectroscopy, and Electrochemistry

Wolfgang A. Herrmann, Paul Kiprof, Kristin Rypdal, Janos Tremmel, Richard Blom, Roger Alberto, Joachim Behm, Rolf W. Albach, Hans Bock, Bahmann Solouki, Janos Mink, Dennis Lichtenberger, Nadine E. Gruhn

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Two key compounds of organometal oxides, methyltrioxorhenium(VII) (1) and trioxo(η 5-pentamethylcyclopentadienyl)rhenium(VII) (2), have been structurally characterized by means of electron diffraction techniques, showing that the ReO3 fragments of these compounds have trigonal-pyramidal structures in the gas phase. The rhenium-carbon distance of the 14e complex 1 amounts to 206.0 (9) pm, which is the shortest Re-C(sp3) bond so far recorded. The pentamethyl-cyclopentadienyl derivative 2 has the longest known rhenium-carbon bond (240.5 (6) pm) due to the size of this particular ir-bonded ligand and the σ/π-donor properties of the oxo ligands (“trans influence”). Infrared and Raman spectra show a much higher triple-bond contribution in the rhenium-oxygen bonds of 1 (force constant k = 8.16 mdyn/Å) compared with 2 (k = 6.99 mdyn/Å). The π-donor qualities of the ring ligand of 2 are considered the major effect to reduce the rhenium-oxygen bond order of this 18e compound since the σ-aryl complex (σ-C6H2Me3)ReO3 (3) has a force constant of k = 8.08 mdyn/Å. According to cyclovoltammetric data, the methyl derivative 1 is more easily reduced (Epc = −0.84 V vs Ag/AgCl, THF, 20 °C) than the half-sandwich congener 2 (Epc = −1.72 V), again reflecting the electronic situation of the two compounds (14e vs 18e, respectively). The first vertical PE ionization energies of 1 and 2, 11.8 and 8.6 eV, differ by 3.2 eV due to their different radical-cation ground states, X(a2n) and X(e,πCp*). The equivalent oxygen lone pair type ionization of 2, IE2v(a2,n0) = 9.9 eV, is lower by 1.9 eV and gives proof of the electron donation from the η5-bonded π-ligand C5Me5. In addition, the PE spectrum of trioxo(η1-mesityl)rhenium(VII) (3) has been recorded: Its first ionization energy of 9.00 eV exceeds the corresponding one of mesitylene by 0.6 eV, thus demonstrating the considerable acceptor effect of the ReO3 substituent group toward an η1-bonded π ligand. The high electric dipole moment of 2 (µ = 6.2 D; benzene, 25 °C) appears reasonable in light of the high polarizability of the C5Me5-Re bond (approximately 4 D); the ReO3 unit has a dipole increment of ca. 2.2 D in 1 and 2. NMR and PE spectra clearly show that the ReO3 functionality is a strong electron-withdrawing substituent, stereoelectronically comparable with the SO3H substituent in organic compounds.

Original languageEnglish (US)
Pages (from-to)6527-6537
Number of pages11
JournalJournal of the American Chemical Society
Issue number17
StatePublished - Aug 1 1991
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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