Principal Investigator: David A. Bruce
Institution: Clemson University
Analysis (rationale for decision):
The efficient synthesis of chiral fine chemicals is essential to the development and production of advanced pharmaceutical and agricultural products. Currently, most chiral chemicals are produced via homogeneous asymmetric catalysis or achiral synthesis coupled with chiral separations. Though homogeneous catalysis has historically provided the highest levels of enantioselectivity, heterogeneous catalysis offers the advantages of catalyst reuse and simplified product purification. Thus, the purview of this activity is the synthesis and modeling of a robust heterogeneous catalyst that exhibits high enantioselectivity for the epoxidation of unfunctionalized olefins. Specifically, helical polymer supports will be used to heterogenize salen metal complexes, which are highly selective asymmetric, homogeneous epoxidation catalysts. The helical polymer supports are amine functionalized phenylene ethynylene oligomers that when combined with inexpensive asymmetric structure directing agents (e.g., -pinene) form helical secondary structures, which have been previously shown to exhibit chiral selectivity in adsorption experiments. The amine functional groups on the exterior of the asymmetric helical polymers will be used as bidentate ligands for the salen metal complexes. Unlike prior polymer supported catalysts, which suffered from reduced enantioselectivity and metal leaching, these catalysts derive their chirality from the asymmetric polymer support and the active metal species are bound via two functional groups to the support, thus, reducing the extent of metal leaching. A further advantage of the proposed catalyst synthesis approach is that molecular modeling studies will be used to guide the design of the optimal catalyst material. The molecular interactions affecting polymer secondary structure formation and reactant adsorption will be studied using molecular dynamics (MD) and replica exchange MD techniques that employ a modified version of the GROMACS simulation code, which we have optimized for studies of these materials. The proposed asymmetric polymer-supported epoxidation catalysts offer the possibility of high enantioselectivity and easy catalyst reuse for the production of chiral epoxides, which are important building blocks for many pharmaceuticals and asymmetric fine chemicals.
Currently, methods to produce chiral products using heterogeneous catalysts are few in number. With the melding of modeling and experimentation, this research will lead to the development of new enantioselective epoxidation catalysts that will help to reduce the cost of producing pharmaceuticals and asymmetric fine chemicals. The research program has also been designed to involve graduate and undergraduate students in all phases of the research. A particular educational advantage of this research effort is that each student will gain experience in molecular modeling and then have the opportunity to apply the results from those studies to the synthesis of novel catalyst materials. The ultimate educational outcomes will be highly motivated undergraduates who will hopefully be inspired to seek out opportunities at the graduate level and doctoral researchers who will be capable of leading a research effort in catalysis or modeling in either industry or academia. Thus, these efforts will lead to both novel catalytic materials and highly educated graduates who will be capable of leading further advances in science and engineering.
