Rational Design of Polymer-Supported Cobalt (III) Salen Catalysts for the Hydrolytic Kinetic Resolution of Terminal Epoxides

Catalyst activity and productivity can be optimized through the use of rationally designed catalyst supports. This thesis reports such a case by using rational designed polymer supports to increase the local concentration of cobalt salen units through proximity control thereby enhancing the bimetallic mechanism of the cobalt salen-catalyzed hydrolytic kinetic resolution (HKR) of terminal. Cyclic supported catalysts based on cyclooctene, reported previously in the Weck group, show a correlation between ring size and catalytic activity, with larger macrocycles being the most active. Unfortunately, the yield of the most active species is only 3%. The first project in this thesis describes a method to overcome this low yield and produce a more active catalyst by using a cross-linkable monomer resulting in the formation of fully crosslinked cyclic supports that increase the yield of the high molecular weight species to 33%. This results in faster catalytic transformations than the original homogeneous cyclic oligomeric catalyst mixture.;The second project is based on grafting the original cyclic oligomeric salen catlysts from poly(styrene) resins. The resulting resin-supported catalysts were shown to be excellent catalysts. When a ten molar excess of water was added to the reaction, a significant rate increase was observed that was attributed to the diol product partitioning into the aqueous phase, maintaining the concentration of the epoxides in the organic phase, where the catalyst is present. This catalyst can be recycled seven times with total turnover numbers exceeding 37,000 while maintaining excellent enantioselectivities.;The third project is based on hydrogenating the oligomeric backbone. According to computational modeling, the activity of the cyclooligomeric cobalt salen catalyst is limited by the restricted rotation of olefins contained in the support. Hydrogenation of the olefins should increase the number of freely rotating bonds, thus, increasing the flexibility of the support. Upon metallation of the hydrogenated cyclooligomeric support, rate enhancements of 5% were observed for the HKR of epichlorohydrin and allyl glycidyl ether. These three rationally designed polymer supported HKR catalysts reported in this dissertation enabled the most active catalysts reported thus far.