The heats of reaction of arene, cycloheptatriene, and cyclooctatetraene complexes of molybdenum tricarbonyl with pyridine yielding (py)3Mo(CO)3 have been measured by solution calorimetry. Reaction of toluene molybdenum tricarbonyl with cyclopentadiene yielding HMo(CO)3C5H5 and with tetrahydrofuran yielding (THF)3Mo(CO)3 have also been studied thermochemically. These measurements yield accurate values for the enthalpy of arene exchange in methylene chloride solution for a number of organomolybdenum complexes. The order of stability: benzene < toluene < cyclooctatetraene < mesitylene < hexamethylbenzene < cycloheptatriene < (tris)-tetrahydrofuran < η5-cyclopentadienylhydrido < (tris)-pyridine spans a range of 31 kcal/mol. The enthalpy of isomerization of cycloheptatriene to toluene is reduced by 7.1 ± 1.2 kcal/mol upon coordination to molybdenum tricarbonyl, indicative of a loss of "resonance" energy for the complexed arene. The MoH bond strength in HMo(CO)3C5H5 is estimated as 66 ± 8 kcal/mol. The importance of entropic factors in arene exchange is discussed.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry
- Materials Chemistry