Learning about Lewis Acid Catalysts using Epoxides

Over nearly 20 years, my research group and I have frequently returned to epoxides as a touchstone, especially for work on supported and homogeneous Lewis acid catalysts. This work has been enabled by many collaborations that will be mentioned throughout, but an especially important one has been a partnership with Dow Chemical Company researchers for more than a decade.

Lewis acidic oxides are used industrially as catalysts for epoxide synthesis from olefins and hydroperoxides. Supported oxides like titania-silica are relatively facile to produce but can be heterogeneous in structure. Over many years, we have developed ways to probe and control this heterogeneity to produce structurally-uniform M-SiO2 materials from bulky precursor molecules. These can give high selectivity and activity, and they serve as a platform for systematic scientific studies. For example, we have recently addressed the role of the support geometry and the solvent in setting activity and selectivity, and we have then designed new materials to tune these interactions.

In the above work, Lewis acid sites efficiently activate hydroperoxides, but they also open the resulting epoxide under a wide range of conditions. In a second set of studies, we have examined the regioselectivity of epoxide alcoholysis using strongly Lewis-acidic fluorinated arylborane catalysts. Presented with the interesting (and useful!) observation that B(C6F5)3 ring-opens terminal epoxides to give the primary alcohol ethers, we developed a microkinetic model that captured the unusually complex behavior of this seemingly-simple catalyst. This model then gave us the insight needed to develop new reaction conditions to further tune the activity of these catalysts.