An investigation of the homolytic dissociation of [η5-C5Me5Cr(CO)3]2 and related complexes. The role of ligand substitution on the solution thermochemistry of metal-metal bond cleavage

W. Carl Watkins, Tilman Jaeger, Colleen E. Kidd, Suzanne Fortier, Michael C. Baird, Gabor Kiss, Gerald C. Roper, Carl Hoff

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Abstract

Thermodynamic parameters for dissociation of the metal-metal bonded dimers [η5-C5R5Cr(CO)2(L)]2 (R = H, L = CO, P(OMe)3; R = Me, L = CO) have been studied by several techniques including variable-temperature FTIR spectroscopy, magnetic susceptibility, NMR spectroscopy, and solution calorimetry. Values for the Cr-Cr bond strength are in the range 11-15 kcal/mol. Results obtained via NMR techniques in this system disagree with all other results probably due to a multiplicity of populated states for the radical monomers. For the radicals {η5-C5H5Cr(CO)2(PR3)} (R = Ph, Et), no sign of dimer formation is found even at -80°C, indicating that the Cr-Cr bond strength is <8 kcal/mol for these compounds. Calorimetric measurements of the heats of reaction of Hg and [η5-C5R5Cr(CO)3]2 forming Hg[η5-C5R5Cr(CO)3]2 have been measured for R = H, Me and indicate average Hg-Cr bond strengths of 20.3 and 20.7 kcal/mol, respectively. Synthetic and spectroscopic details are described for [η5-C5Me5Cr(CO)3]2 as well as its structure as determined by X-ray crystallography. The Cr-Cr distance, 3.3107 (7) Å, is longer than that reported for [η5-C5H5Cr(CO)3]2; however, the increased tendency to form radicals for this complex is due more to entropic than enthalpic factors.

Original languageEnglish
Pages (from-to)907-914
Number of pages8
JournalJournal of the American Chemical Society
Volume114
Issue number3
StatePublished - Dec 1 1992

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Thermochemistry
Carbon Monoxide
Dimers
Substitution reactions
Metals
Ligands
X ray crystallography
Calorimetry
Magnetic susceptibility
Nuclear magnetic resonance spectroscopy
Monomers
Nuclear magnetic resonance
Spectroscopy
Thermodynamics
Temperature
X Ray Crystallography
Fourier Transform Infrared Spectroscopy
Spectrum Analysis
Magnetic Resonance Spectroscopy
Hot Temperature

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

An investigation of the homolytic dissociation of [η5-C5Me5Cr(CO)3]2 and related complexes. The role of ligand substitution on the solution thermochemistry of metal-metal bond cleavage. / Carl Watkins, W.; Jaeger, Tilman; Kidd, Colleen E.; Fortier, Suzanne; Baird, Michael C.; Kiss, Gabor; Roper, Gerald C.; Hoff, Carl.

In: Journal of the American Chemical Society, Vol. 114, No. 3, 01.12.1992, p. 907-914.

Research output: Contribution to journalArticle

Carl Watkins, W. ; Jaeger, Tilman ; Kidd, Colleen E. ; Fortier, Suzanne ; Baird, Michael C. ; Kiss, Gabor ; Roper, Gerald C. ; Hoff, Carl. / An investigation of the homolytic dissociation of [η5-C5Me5Cr(CO)3]2 and related complexes. The role of ligand substitution on the solution thermochemistry of metal-metal bond cleavage. In: Journal of the American Chemical Society. 1992 ; Vol. 114, No. 3. pp. 907-914.
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AU - Carl Watkins, W.

AU - Jaeger, Tilman

AU - Kidd, Colleen E.

AU - Fortier, Suzanne

AU - Baird, Michael C.

AU - Kiss, Gabor

AU - Roper, Gerald C.

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