This award in the Division of Chemistry to Alan Goldman at Rutgers University centers on the oxidative addition and reductive elimination of C-H bonds by late transition metal complexes. The factors that govern the thermodynamics, kinetics and selectivity of C-H, C-C, C-X and X-H bond addition and elimination with such complexes will be elucidated. As the insertion of unsaturated substrates into M-C, M-H, and M-X bonds is likely the most difficult step in many potential catalytic cycles related to C-H activation, these insertions will also be investigated. The approach will be based on the extensive integration of: 1) The synthesis of new late metal complexes, particularly pincer-ligated metal complexes, which offer high stability together with the ability to explore variation of ancillary coordinating groups in a well controlled fashion, while leaving open coordination sites for substrate activation and subsequent steps. 2) Mechanistic studies of addition/eliminations and insertion/de-insertions. 3) Screening new complexes for a broad array of stoichiometric and catalytic reactions. The latter will include additions of CH and X-H to unsaturates (olefins, alkynes, CO), and dehydrocoupling. When the potential for asymmetric catalysis exists, chiral pincer complexes will be investigated. The reactivity of C-H addition products will be investigated with respect to functionalization of the resulting M-C and M-H bonds (e.g. insertions) and for the effect of C-H addition on remote sites (e.g. increased susceptibility toward nucleophilic attack on homo- and heteroaromatics as a result of metallation). 4) Computational (DFT) studies will be used to provide leads for synthesis. Computational methods will be tested and calibrated by mechanistic and screening studies. New functionals and basis sets will be investigated to increase predictive value, and thus the ability to design and improve new catalysts.
The development of catalytic C-H bond transformations, as well as reactions in which C-O and C-F bonds are broken or formed, has vast potential impact in areas ranging from the synthesis of fuels to pharmaceuticals. Students and postdoctoral associates will receive broad training in synthesis, analysis, and in the principles and strategy of catalyst design and development, including the use of computational methods. Graduate students, postdoctoral associates and undergraduates will gain industrial perspectives through collaboration with Chevron. Every summer, through the Project SEED program, high school students from under-represented backgrounds are exposed to research in this area and come to view of science as a portal to opportunity rather than a body of knowledge to be received.
Catalysis accounts for nearly 20% of United States GDP and contributes indirectly to an even larger fraction. Our work under the auspices of NSF funding has contributed at multiple levels to the development of this important area of science. The project has comprised a strong interplay between elucidating understanding at a fundamental level, and the design and synthesis of new catalytic systems with actual or potential practical value. With respect to new catalytic systems, we have been particularly successful in the development of catalysts for the cleavage and formation of carbon-oxygen (C-O) bonds. Such reactions have great potential in organic synthesis, most obviously in the context of pharmaceutical candidates, but also for new materials, agrochemicals and many other products of chemistry-related industries. In addition, there is great interest in C-O cleavage reactions for the conversion of biomass to fuels and high-value chemicals. Specifically, we have reported (J. Am. Chem. Soc. 2013, 135, 5127) the stoichiometric cleavage of a wide range of C-O bonds by iridium-pincer complexes, and have determined that these reactions proceed via the initial addition (cleavage) of C-H bonds. This unanticipated pathway opens a new strategy for the development of catalysts for C-O bond cleavage. Based on this result we developed a catalytic system for the reverse reaction, C-O bond formation, which was shown to proceed via (i) O-H addition, (ii) olefin insertion into the resulting metal-O bond, and (iii) elimination (formation) of a C-H bond (J. Am. Chem. Soc. 2013, 135, 15062). Following that work, we found that with the correct catalyst and choice of reaction conditions, we could adapt this system for catalytic C-O bond cleavage. Specifically we were able to effect dehydroaryloxylation, a rare fully atom-economical (i.e. requiring no additional reagents) method for the cleavage of ether C-O bonds (Angew. Chem., Intl. Ed. 2014, 53, 10160). A provisional patent application covering some of this work has been filed. Carbon-hydrogen (C-H) bonds are the most common bonds in organic chemistry; accordingly, the ability to manipulate them selectively is one of the most important targets in catalysis. Our fundamental work has contributed significantly to our understanding of the kinetics and thermodynamics of cleavage of C-H bonds. We have also developed a new class of C-H activation (bond cleavage) reaction: acid-catalyzed oxidative addition (J. Am. Chem. Soc. 2014, 136, 8891). This approach indicates promise as a first step toward development of catalysts for carbonylation (the incorporation of carbon monoxide) of hydrocarbons. This has broad potential for the more efficient use of fossil resources, particularly natural gas, as well as potential applicability for the production of liquid fuels from CO2 and sustainable energy sources. Additionally we have recently found a novel system for the incorporation of olefins into arene C-H bonds (Abstracts of Papers, 247th ACS National Meeting & Exposition, Dallas, TX, 2014, INOR-895). Theoretical studies have increased our understanding of insertion of olefins into metal-carbon bonds (Organometallics 2012, 31, 4680). This has important implications for the development of catalysts for olefin polymerization or oligomerization, as well as catalysts for novel reactions such as hydrocarbylation. A combined theoretical-experimental study on C-C bond cleavage (Dalton Trans. 2014, 43, 16354) is highly relevant to the reverse reaction, C-C bond formation, which is one of the most important specific elementary steps in modern transition-metal catalyzed chemistry. The PI and many of the students and postdocs working on the project have also been strongly involved in communicating the excitement and importance of chemical research to those outside the profession. Former graduate students Katherine Field and David Laviska (both now Ph.D.â€™s) co-founded "Learning Enabled through Experimental Design and Analysis at Rutgers". This program enables high school students to design their own science experiments and thereby learn that science is, first and foremost, an active inquiry, rather than the passive accumulation of knowledge or even the entertainment of class demonstrations. Dr. Laviska and the Principal Investigator of this grant have also initiated, in collaboration with Prof. Abby Oâ€™Connor of TCNJ, and Dr. Jonn McCollum of the Liberty Science Center in Jersey City, the design of "Molecule Magic", now permanently featured at Liberty Science Center (the major science museum of New Jersey) as part of a larger exhibition, "Energy Quest". Molecule Magic is an interactive touch-table game that allows visitors to "virtually synthesize" common household materials such as aspirin and polyolefins (the latter with use of a "virtual catalyst"). Many thousands of children and adults have participated in this very enjoyable exposure to chemistry. Other science centers around the country have expressed interest in adopting Molecule Magic. Efforts to achieve even broader exposure of its key concepts, through translation to personal electronics platforms for formal or informal science education, are now underway.