Professor Greg A. Slough of Kalamazoo College is supported by the Chemical Catalysis Program in the Division of Chemistry to investigate the catalytic properties of diastereomeric Mn-salen complexes, to be prepared through a combinatorial library approach and immobilized within polystyrene/divinyl benzene resin beads. The effect of the salen complex, the resin type and solvent swelling on the microenvironment of the immobilized salen catalysts will be probed by infrared spectroscopy, and the epoxidation of alkenes on immobilized salens having differing structures will be investigated. The goal of this research is to understand the effect of confinement within organic polymer networks on organic chemical catalysis. Understanding the effects of confinement could potentially render metal catalysts recyclable and less of an environmental burden. Undergraduate students at Kalamazoo College will be exposed to a valuable research experience involving instrumentation, synthesis, and catalysis.
The term catalytic has nearly reached the common vernacular in modern society. We buy commercial products based upon whether this item or that item has a catalytic finish or whether its operation involves a catalytic process. This grant investigated how the properties of a catalyst or a reactive chemical are affected when they are immobilized or encapsulated within a polymer network. The polymer used in this study has many of the same characteristics as the white styroform used for hot beverage cups. The motivation for encapsulating a catalyst within polystyrene/styroform is easy to understand. The polymeric bead, as seen in a beverage cup, can be filtered at the end of a reaction thus presumably removing the catalyst from the product(s). Immobilized catalysts have been explored repeatedly over the past three decades, however, their performance is quite lacking when compared to similar catalysts in solution. In this study we utilized infrared spectroscopy and chemical recognition method in examine the differences within different samples of polystyrene. The infrared allowed us to see differences in bond stretches between non-mirror image stereoisomers. The chemical recognition method allowed us to selectively hydrogen-bond one enantiomer of benzoin to a complementary chiral compound encapsulated within the polymer. This study identified two simple tests based on bond stretching and chemical recognition to evaluate polymers for their internal environmental features. We evaluated the internal features by installing the same chiral compound in three polymer samples from different manufacturers and then conducting the same chemical activity. For example, we mixed the polymer with racemic benzoin. Under identical conditions, we found a 22% difference among the three samples in their ability to hydrogen-bond to (+)-benzoin. The simplicity of these methods make them ideally suited as a pre-test of polymeric samples as they are chemically modified and turned into immobilized catalysts.
