This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor Wenbin Lin at the University of North Carolina to develop rational synthetic strategies toward homochiral and highly porous metal-organic coordination networks (MOCNs) and to explore their applications in heterogeneous asymmetric catalysis and chiral separations. Three key issues concerning heterogeneous asymmetric catalysts based on homochiral porous MOCNs will be addressed: rational synthesis of homochiral MOCNs with permanent porosity and appropriate functionalities, development of novel strategies for the synthesis of highly porous homochiral MOCNs from typically unresolvable (achiral) building blocks, and the utilities of homochiral porous MOCNs in practical enantioselective catalysis and separations. Highly porous chiral MOCNs with desirable functional groups and appropriate metal linkers will result from the proposed research, which should possess tailorable chiral pockets and functionalities that are exploitable for enantioselective separations and catalysis.
The proposed research will develop new bottom-up approaches towards efficient heterogeneous asymmetric catalysts that can be readily recycled and re-used and can prevent the leaching of often toxic metals from the catalysts into the organic products. Graduate students and postdoctoral research associates participating in the proposed interdisciplinary research will be trained with the skills that are crucial to their future careers as Ph.D. chemists. The proposed research will also be integrated into the training of undergraduates and high school students.
Heterogeneous catalysis is responsible for the production of the majority of commodity chemicals. In contrast, many of value-added fine chemicals (particularly optically active ingredients for the pharmaceutical, agrochemical, and fragrance industries) are produced by homogeneous catalytic technologies primarily because of the lack of efficient heterogeneous catalysts. We have developed a number of chiral, porous materials based on metal-organic coordination networks (MOCNs) for catalyzing highly enantio- and stereo-selective organic transformations in this project. Specifically, we have accomplished the following: (1) we have developed new strategies to prepare highly porous chiral MOCNs as well as establishing novel techniques to characterize such porous materials; (2) we have established the first example of chirality-dependent catenation isomerism in MOCNs; (3) we have established a new strategy to stabilize porous MOCNs by using highly branched polycarboxylic acid bridging ligands; (4) we have designed a series of isoreticular chiral MOCNs containing metal-Salen building blocks and used them to catalyze asymmetric epoxidation of unfuntionalized alkenes with very high enantioselectivities (up to 99%) and activity (up to 4000 TON); (5) we have demonstrated the ability to synthesize isoreticular homochiral MOCNs with tunable channel sizes and determined the influences of channel sizes on their catalytic performances; (6) we have observed single-crystal to single-crystal crosslinking of two interpenetrating networks in chiral MOFs and correlated this structural findings with its catalytic performance; (7) we have discovered the first chiral MOF that can carry out multi-step organic transformations sequentially. This allows multi-step manipulations of the organic starting materials with a single solid catalyst; and (8) we have observed the actuation of asymmetric cyclopropanation catalysts via reversible single crystal-to-single crystal reduction. We have also observed the tuning of catalytic activities by framework interpenetration in this MOF series. In all, we have published twenty peer-reviewed papers and two book chapters that acknowledge the funding support from this NSF grant. Our work in this area has not only helped establish chiral, porous MOCNs as viable heterogeneous asymmetric catalysts but also uncovered a number of interesting phenomena that have not been observed before. Our work thus promises to lead to innovative MOCN-based chirotechnology that is competitive and profitable as well as has the ability to optimize health and safety and ensure environmental stewardship. In addition to its potential impact on our nation’s new chirotechnologies, our work also contributes to NSF’s mission on the promotion and integration of research and education. This funding support allows the PI to train a large number of personnel, including four postdoctoral fellows, one visiting professor, three graduate students, two visiting graduate students, and four undergraduate students. These personnel have been trained with the skills that are crucial to their future careers as chemists. Half of these personnel are female, and one of the undergraduate students is from the underrepresented minority group. The funding of this project thus has a significant impact on the PI’s efforts in not only training undergraduate students, graduate students, and postdoctoral research associates, but also helping diversifying the future chemical industry workforce by mentoring underrepresented populations (underrepresented minority and female students/postdoctoral fellows).
