The heats of hydrogenation of the metal-metal bonded complexes [M(CO)3C5H5]2 (M = Cr, Mo, W)

John T. Landrum, Carl Hoff

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Abstract

Direct measurement of the enthalpy of decomposition of HCr(CO)3C5H5 to [Cr(CO)3C5H5]2 and H2 was made by differential scanning calorimetry. The heat of hydrogenation of 1,3-cyclohexadiene by HM(CO)3C5H5 for M = Cr, Mo, and W was measured by solution calorimetry. The enthalpies of iodination of [M(CO)3C5H5]2 and HM(CO)3C5H5 were measured for M = Mo and W. These data have been used to calculate the heats of hydrogenation for each of the metal-metal bonded dimers, [M(CO)3C5H5]2 (M = Cr, Mo, and W). C5H5(CO)3M-M(CO)3C5H5(s) + H2(g) → 2HM(CO)3C5H5(s). Addition of hydrogen has been found to be exothermic for M = Cr, W (-3.3 kcal/mol and -1.5 kcal/mole, respectively) but endothermic for M = Mo (+6.3 kcal/mol). These results are consistent with the trend of increasing MH bond strengths upon descending Group VI. Addition of H2 to [Cr(CO)3C5H5]2 is favored by the unusually weak chromium-chromium bond.

Original languageEnglish
Pages (from-to)215-224
Number of pages10
JournalJournal of Organometallic Chemistry
Volume282
Issue number2
DOIs
StatePublished - Mar 5 1985

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Hydrogenation
Coordination Complexes
Carbon Monoxide
Metal complexes
hydrogenation
Enthalpy
chromium
Chromium
heat measurement
Hot Temperature
enthalpy
Metals
heat
Calorimetry
Dimers
metals
Differential scanning calorimetry
dimers
Decomposition
trends

ASJC Scopus subject areas

  • Biochemistry
  • Chemical Engineering (miscellaneous)
  • Inorganic Chemistry
  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Materials Science (miscellaneous)
  • Materials Chemistry

Cite this

The heats of hydrogenation of the metal-metal bonded complexes [M(CO)3C5H5]2 (M = Cr, Mo, W). / Landrum, John T.; Hoff, Carl.

In: Journal of Organometallic Chemistry, Vol. 282, No. 2, 05.03.1985, p. 215-224.

Research output: Contribution to journalArticle

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AB - Direct measurement of the enthalpy of decomposition of HCr(CO)3C5H5 to [Cr(CO)3C5H5]2 and H2 was made by differential scanning calorimetry. The heat of hydrogenation of 1,3-cyclohexadiene by HM(CO)3C5H5 for M = Cr, Mo, and W was measured by solution calorimetry. The enthalpies of iodination of [M(CO)3C5H5]2 and HM(CO)3C5H5 were measured for M = Mo and W. These data have been used to calculate the heats of hydrogenation for each of the metal-metal bonded dimers, [M(CO)3C5H5]2 (M = Cr, Mo, and W). C5H5(CO)3M-M(CO)3C5H5(s) + H2(g) → 2HM(CO)3C5H5(s). Addition of hydrogen has been found to be exothermic for M = Cr, W (-3.3 kcal/mol and -1.5 kcal/mole, respectively) but endothermic for M = Mo (+6.3 kcal/mol). These results are consistent with the trend of increasing MH bond strengths upon descending Group VI. Addition of H2 to [Cr(CO)3C5H5]2 is favored by the unusually weak chromium-chromium bond.

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