The alcoholysis of terminal epoxides is an industrially important reaction that yields monoether alcohols with either a primary alcohol (denoted P1) or a secondary alcohol (P2) as the product. Aliphatic epoxides typically give P2 due to the favorable sterics of alcohol attack at the less hindered terminal carbon, regardless of the catalyst. Here, we discuss the mechanism of the homogeneous Lewis acid catalyst tris(pentafluorophenyl)borane, B(C6F5)3, also known as BCF, for the selective alcoholysis of terminal aliphatic epoxides to the unexpected P1 regioisomer. Our joint academic and industrial team has seen that alcoholysis regioselectivity over BCF and related species is strongly dependent on nucleophile identity, residual water concentration, temperature, conversion, and external additives in ways that are inconsistent with simple Lewis acid mechanisms being the sole reaction pathway. Therefore, we sought out other potentially relevant catalytic species. BCF is known to form strong H-bound complexes of the type BCF(H2O)(HBA)2, where HBA is any H-bound adduct such as residual water, the alcohol nucleophile, the products, or the epoxide, and microkinetic modeling indicated that such complexes participate in kinetically relevant pathways under reaction conditions.[1] The general structure of the model has proven capable of explaining results over a wide set of conditions,[2] including the pronounced increase in selectivity induced by catalytic amounts of cis-1,2 and 1,3 diols as HBAs.[3] This talk will discuss findings specific to this catalytic system but will also broadly address topics such as the often-overlooked complexity of ‘molecularly-precise’ catalysts such as this one, and the utility of expansive microkinetic models such as employed here.

Understanding B(C6F5)3-catalyzed epoxide alcoholysis

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.