Abstract
Currently accepted hydrogenation mechanisms of Shvo’s catalyst include an activation step in which the inactive ruthenium dimer undergoes scission to form two different catalytic species. In this study, two-dimensional infrared spectroscopy (2D-IR) of the metal carbonyl vibrations of Shvo’s catalyst was used to monitor early reaction dynamics for the inactive and activated catalyst. Kinetic analysis of exchange peaks in the 2D-IR spectra demonstrate that thermally activated intramolecular proton exchange occurs on the ultrafast time scale. The results indicate an activation barrier for proton transfer of 2.1 kcal/mol and an upper limit for the dimer scission rate constant of 1.3 × 1011 s–1, which is well above the previously reported value. Deprotonation of the dimer leads to a pseudo stable species that remains dimeric at the ruthenium–hydride bridge for several hours. 2D-IR spectroscopy of this species shows that proton transfer is turned off, as expected. The data reveal new mechanistic details of the ...
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