Catalysts of the form RuCp(PR2R'), with R' an N-heterocyclic pendant base, have been employed with striking efficacy in the isomerization of monoalkenes to transfer the double bond towards the thermodynamically favored endpoint.  In unsubstituted alkenes, this transfers a terminal double bond towards the interior.  We report the results of classical kinetics analysis to time- and temperature-dependent NMR measurements of concentrations in the reaction mix for a variety of substituted and unsubstituted alkenes, from butene to decenol.  Of particular interest are two aspects of the catalyst selectivity: the preferential formation of (E) configurations, and the distinct reaction profile when the Cp ring is replaced by Cp*, which selectively slows the reaction to allow effective isolation of intermediate alkenes.  Rate constants were determined by least squares analysis of the data, with the approach to equilibrium often allowing resolution of reverse rate constants.  Activation energies are reported for the reactions of the Cp catalyst with butene and pentene, where temperature-dependent data are available.  In other cases, relative activation energies have been estimated by assuming similar Arrhenius pre-exponential factors for the rate-determining steps at each stage of isomerization.

Kinetics analysis of selective organometallic catalysts for alkene isomerization

2019 Fall National Meeting

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