cs8b02632_si_001.pdf (1.83 MB)
Mechanism of Regioselective Ring-Opening Reactions of 1,2-Epoxyoctane Catalyzed by Tris(pentafluorophenyl)borane: A Combined Experimental, Density Functional Theory, and Microkinetic Study
journal contribution
posted on 2018-10-09, 00:00 authored by Ying Yu, Youlong Zhu, Mihir N. Bhagat, Arjun Raghuraman, Kurt F. Hirsekorn, Justin M. Notestein, SonBinh T. Nguyen, Linda J. BroadbeltA nonconventional,
water-mediated catalytic mechanism was proposed
to explain the effects of residual water on the reactivity and regioselectivity
of tris(pentafluorophenyl)borane catalyst in the ring-opening reaction
of 1,2-epoxyoctane by 2-propanol. This nonconventional mechanism was
proposed to operate in parallel with conventional Lewis acid-catalyzed
ring-opening. Microkinetic modeling was conducted to validate the
proposed reaction mechanism, with all kinetic and thermodynamic parameters
derived from density functional theory (DFT) calculations. Experimental
data at a variety of temperatures and water contents were captured
by the model after adjustments within reasonable limits set by experimental
benchmarking and accuracy of theory of a small subset of parameters.
In addition, the microkinetic model was able to generate accurate
predictions at reaction conditions that were not used for parameter
estimation. Detailed analysis of the net reaction rates showed that
>95% of the reaction flux passed through conventional Lewis-acid
pathways
at water levels <500 ppm, even though the borane-epoxide adduct
never accounted for more than 30% of the catalyst speciation under
reaction conditions. With increasing water, as much as 80% of the
reaction flux utilized water-mediated reaction intermediates. Within
the water-mediated mechanisms, different hydrogen bond acceptors (HBAs)
influenced the reaction regioselectivity. Overall, this validated
mechanism and microkinetic model provided better understanding of
industrially important ring-opening catalysis with this catalyst in
the presence of water and could facilitate future improvement of catalyst
regioselectivity and reactivity.