Methyl group geometries, C–H bond properties and internal rotation in dicarbonyl(η5-cyclopentadienyl)methyl-iron(II) and -ruthenium(II), [MMe(η5-C5H5)(CO)2](M = Fe or Ru)
- 1 January 1995
- journal article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 24,p. 3955-3961
- https://doi.org/10.1039/dt9950003955
Abstract
Vibrational spectra have been recorded for the CH3, CD3 and CHD2 isotopomers of [MMe(cp)(CO)2](M = Fe or Ru; cp = cyclopentadienyl). The effects of Fermi resonance were considered in detail and the resonance-corrected CH and CD stretching frequencies used to predict methyl group geometries. Only one ‘isolated’ CH stretching absorption, νisCH, is observed in each CHD2 isotopomer. The results are not consistent with a model in which the methyl groups are subject to an effective barrier to internal rotation, with significant variation of CH bond length with orientation. The spectra are best interpreted in terms of an essentially freely rotating methyl group in which the individual CH bonds undergo a small variation in bond length with rotational angle. The larger barriers which occur in the tricarbonyl compounds [MMe(cp)(CO)3](M = Cr, Mo or W) are likely to be primarily steric in origin, whereas that in [TiMe(cp)Cl2] may arise from an interaction between a CH bonding pair and an unoccupied titanium orbital. The Ru–CH3 bond appears to be slightly weaker than the Fe–CH3 bond, in contrast with results for earlier groups in the d block, in which M–CH3 bond strengths increase down each group.Keywords
This publication has 25 references indexed in Scilit:
- Infrared Spectrum of Cyclopentadienyltrimethyltitanium(IV) and Investigation of the Methyl Group Geometry through Partial Deuteration StudiesOrganometallics, 1995
- Carbon-hydrogen stretching vibrations as a probe of the structure of unstable organometallic speciesOrganometallics, 1989
- Vibrational spectra of trimethyl gallium species in relation to the force field and methyl group internal rotationSpectrochimica Acta Part A: Molecular Spectroscopy, 1987
- Infrared spectra and methyl group properties in dicyclopentadienyldimethyl-titanium(IV), -zirconium(IV) and -hafnium(IV)Journal of Organometallic Chemistry, 1986
- Vibrational spectra and assignments of MeMn(CO)5 and MeRe(CO)5 species, energy-factored and A1 force fields, and a further effect of free internal rotationJournal of the American Chemical Society, 1986
- Isolated CH stretching frequencies, methyl group geometry, and methyl CH bond lengths and strengths in tricarbonyl(η5-cyclopentadienyl)methyl-chromium(II), -molybdenum(II), and -tungsten(II)J. Chem. Soc., Dalton Trans., 1985
- Infrared spectra of methylmanganese pentacarbonyl and methylrhenium pentacarbonyl species: methyl group geometry and the effects of internal rotationJournal of the American Chemical Society, 1984
- New light on the stretching vibrations, lengths and strengths of CH, SiH and GeH bondsJournal of Molecular Structure, 1984
- Isolated CH stretching frequencies, methyl group geometry and dissociation energies in dimethyl zinc, cadmium and mercurySpectrochimica Acta Part A: Molecular Spectroscopy, 1980
- Individual CH bond strengths in simple organic compounds: effects of conformation and substitutionChemical Society Reviews, 1978