The Chemical Catalysis Program supports Professor David E. Bergbreiter at Texas A&M University for a research project that will use phase-selectively soluble polymer-bound catalysts in immiscible solvent mixtures to address important challenges in synthesis and catalysis and will have an effect on the areas of catalysis, synthesis, Green chemistry and polymer chemistry. The proposed research will extend the PI's past discoveries on the use of polymer-bound catalysts in homogeneous solutions to conduct reactions in oil-in-oil emulsions. The catalyst immobilization chemistry proposed is based principally on the properties of the soluble polymer support. Using chemistry developed in prior work will allow the preparation of a variety of homogeneous catalysts, and phase segregate and concentrate them in the discontinuous phase of oil-in-oil emulsions. Transesterification catalysts, organometallic catalysts and organocatalysts will all be studied. The reactions to be studied are macrocyclizations using several different methods such as transesterification, olefin metathesis, Baylis-Hilman reactions, and carboxylic acid additions to epoxides.
With the support of the Chemical Catalysis Program in the Chemistry Division at the National Science Foundation, Dr. Bergbreiter will perform research that will not only apply to multiple types of macrocyclizations (lactones, epoxides, Baylis-Hilmman), but also include careful and clever studies designed to optimize reaction rates, catalyst recovery, and removal of catalysts from products. Professor Bergbreiter?s work has also had an impact in the technology arena where earlier work was the basis of a recently described process by DuPont for a commercially viable route to clearcoats containing low volatile organic compounds (VOC) for automotive finishing applications. Broader impacts of this work include the training of undergraduate, PhD, and postdoctoral students. Professor Bergbreiter has had success introducing undergraduates both from Texas A&M and elsewhere to research. His research program is expected to continue to involve a significant percentage of students from underrepresented groups. The current program included 34% women and 38% students from underrepresented groups among the undergraduates or graduate students who worked on the project. These percentages will increase to 50% in the future by targeting schools in Texas that serve underrepresented groups. International outreach will be achieved by working with an undergraduate institution in Qatar, and with universities in Japan and Thailand, which will broaden the cultural experiences of his students.
Our NSF-supported work was directed toward exploring how soluble polymers could be used to facilitate homogeneous catalysis. Homgeneous catalysis is a fundamental process that is widely used to prepare modern polymers, chemical intermediates, basic chemicals and pharmaceuticals. These processes often use expensive or toxic prescious metals like palladium as catalysts with complicated ligands that optimize catalyst performance. Recycling these ligands and catalysts and separating their residues from products is thus both econimically and environmetally important. Such existing separation processes however often are complicated and produce chemical waste. Such processes would be much greener processes if these catalysts could more easily be separated from products and/or reused. Our proposal was aimed at exploring basic chemistry using soluble polymers as supports that could serve as a platform for solutions to these problems . As shown in a graphical summary in Figure 1, we made significant strides in meeting these goals. We showed that physical separations involving little or no added solvent could be effected in important catalytic transformations using many examples of soluble polymer bound catalysts. We explored new catalysts, new more environmentaly benign solvents, and designed and synthesized new types polymers that simplify catalyst/product separation. We then demonstrated the applicability of these general approaches using important homogeneous catalysis reactions. Specific examples of the intellectual impact of our work include the description of ways to encapsulate and sequester a catalyst in solid hydrocarbon waxes that both easily separate from products but also protect catalysts from some types of adventitious decompositon in workup of batch type reactors. We showed that very inexpensive and nontoxic oligomers of polyisobutylene and polyethylene are easily modified with sophisticated catalyst ligands and that these polyolefins can serve as phase anchors to reduce catalyst residues in products to <1% of the charged catalyst. This allows stable catalysts to be reused dozens of times decreasing costs for reactions and increasing the sustainability of precious metal catalysts. Seminal studies that compared ligands on soluble oligomers with conventional low molecular weight ligands showed the two had equivalent reactivity in coordination to metals - an important result that shows that these sorts of catalysts will accurately mimic existing catalysts. We showed that unfunctionalized hydrocarbon oligomers that resemble candle wax can be used in place of volatile and toxic hydrocarbonsolvents. Finally, we showed that polymers with thermoresponsive properties can not only separate catalysts from products but also affect pH of aqueous solutions, leading to a potential way to make smart general acid and base catalysts that could affect biocatalysis. The results of these studies had a a variety of broader impacts. First, we communicated our results to the broader community through peer-reviewed publications. Second, outreach activities including demonstration of these separation chemistry to the general public at annual university open houses led to an experiment that we are now incorporating in our Department's road show for K-12 students. Third, personnel on the project described these results publically in poster and oral presentations at local, regional, national, and international meetings. Fourth, we successfully incorporated our studies in undergraduate courses and subsequently published an article detailing how we used these examples to illustrate important precepts of polymer chemistry in sophomore organic chemistry courses. Finally, these studies provided training to a diverse group of undergraduate, graduate, and postdoctoral students who have subsequently gone on to professional school, to industrial positions or to academic positions.
