Mechanism of Regioselective Ring-Opening Reactions of 1,2-Epoxyoctane Catalyzed by Tris(pentafluorophenyl)borane: A Combined Experimental, Density Functional Theory, and Microkinetic Study

Abstract

A 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.

Mechanistic insight into B(C6F5)3 catalyzed imine reduction with PhSiH3 under stoichiometric water conditions

“…7 Broadbelt et al proposed a transition state in which (C 6 F 5 ) 3 B-OH 2 donates a proton in ring-opening reactions of epoxyoctane. 8 Our group recently conrmed that B(C 6 F 5 ) 3 catalyzed reductive amination of aldehydes with alkoxyamines can proceed under moist conditions with hydridosilanes as reducing agents. 9…”

Chemoselective Dual Functionalization of Phenols via Relay Catalysis of Borane with Different Forms

“…[10][11][12] Unlike other Lewis acids, the borane is not only water-tolerant but its hydrate is also a powerful Brønsted acid that has been employed in diverse organic reactions. [13][14][15][16][17][18] Even so, the area of relay catalysis with B(C 6 F 5 ) 3 and its hydrate is still underdeveloped. [19][20][21][22][23][24][25][26] Organic compounds that contain phenol motifs are not only fundamental chemical feedstocks, but also have many impressive biological activities.…”

Synthesis of complex unnatural fluorine-containing amino acids

“…Due to their highly electron deficient nature, perfluoroaromatics can have significant effects on the electronics of molecular systems [ 60 ]. Perfluoroaromatic moieties have therefore seen use in materials [ 61 ], catalysis [ 62 , 63 ] and organic synthesis [ 64 , 65 ], and have been exploited in peptide [ 66 , 67 ] and peptoid chemistry [ 68 ]. Access to highly fluorinated amino acids is therefore an area of much research, with several reports detailing the synthesis of aromatic perfluorinated amino acids.…”