The hydrogenation of α-methylstyrene by tricarbonyl(cyclopentadienyl)hydride compounds of tungsten and molybdenum; support for a radical mechanism - L. Sweany, R.; S. Comberrel, D.; F. Dombourian, M.; A. Peters, N. (Elsevier)
Rates of reaction of the hydrides of tungsten and molybdenum of the form HM(η5-C"5H"5(CO)"3, with β-methylstyrene have been determined. The rate law is first order in olefin and in hydride. A mechanism involving a rate limiting step of hydrogen atom transfer to the olefin is consistent with the rate law, isotope effect and the absence of CO inhibition. The activation enthalpy for the reactions of HW(η5-C"5H"5)(CO)"3 and HMo(η5-C"5H"5)(CO)"3 are 97.5 +/- 4.2 and 89.1 +/- 3.3 kJ/mol, respectively. The rate constant for the reaction of styrene and HW(β5-C"5H"5)(CO)"3 is approximately that of β-methylstyrene, while β-methylstyrene was not observed to react under the conditions of the previous determinations. This suggests that attack by the hydride occurs at the β-carbon and this process is inhibited by substituents at that location.
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