With a rising global population and increasing industrialization, the need to establish new and energy-efficient chemical conversion schemes is vital. Investigations into the discovery and implementation of innovative conversion schemes could lead to new ways by which chemical feedstocks are processed and recycled with minimal energy input. However, many aspects of the underlying science behind such strategies must be developed prior to large-scale implementation. To address these issues, our research program is uncovering new strategies to develop catalytic methods for energy recycling and delivery. The Szymczak group uses synthetic inorganic and organometallic chemistry to develop new catalytic methods for energy delivery, storage and recycling. We currently have two main foci: (1) the regeneration of spent hydrogen storage materials, (2) and the design of new synthetic catalysts for small molecule activation.
Regeneration of chemical hydrogen-storage materials by (electro)catalytic hydrogenation. Hydrogen storage in boron-nitrogen containing molecules is particularly attractive because of the high achievable gravimetric densities of H2. However, while the dehydrogenation of B-N materials (such as ammonia borane) to afford H2 is highly studied, the regeneration of spent B-N fuels remains a coveted goal that needs to be addressed before B-N compounds have any possible utility as hydrogen storage materials. We are targeting the catalytic re-hydrogenation of a high wt% B-N material with low-energy reactants. Current regeneration protocols utilize unfavorable reaction conditions, including high-energy reductants, therefore, a regeneration cycle incorporating a low-energy reduction pathway, or one that uses stoichiometric hydrogen, will change the paradigm for B-N materials, and allow for a truly reversible hydrogen storage material to be realized.
Using Secondary Coordination Sphere Interactions to Modulate Substrate Binding and Activation Another avenue of our research program focuses on establishing new ways by which molecular catalysts can be tuned by the incorporation of pendent functional groups within a metal's secondary coordination sphere environment. We are using these appended functional groups (hydrogen bond donor/acceptors, or Lewis acid/bases) to augment reactivity of the central transition metal in order to promote the activation/delivery of small molecules to appropriate substrates.
In addition to using these functional group appended ligands for substrate activation/reactivity chemistry, we are exploring how ground-state stabilization of substrates can be achieved by utilizing appropriately-designed ligand architectures through metal-ligand cooperativity. A large synthetic effort is required to develop these alternative energy recycling strategies. Therefore, our group uses a variety of inorganic synthetic air-free techniques (Schlenk, glovebox, high pressure reactivity) to prepare the new molecular constructs and use a battery of physical methods (e.g. NMR and IR spectroscopy, X-ray crystallography, electrochemistry) in order to assess their catalytic efficacy. When successful, our efforts will change the way that we think about energy-recycling/storage strategies.
Tseng, K-N T.; Rizzi, A. M.; Szymczak, N. K.*; Oxidant-Free Conversion of Primary Amines to Nitriles, J. Am. Chem. Soc., 2013, 135, 16352–16355
Tseng, K-N T.; Kampf, J. W.; Szymczak, N. K.*; Base-Free, Acceptorless, and Chemoselective Alcohol Dehydrogenation Catalyzed by an Amide-Derived NNN-Ruthenium(II) Hydride Complex. Organometallics, 2013, 32, 2046-2049
Tutusaus, O.; Ni, C.; Szymczak, N. K.*; A Transition Metal Lewis Acid-Base Triad System for Cooperative Substrate Binding. J. Am. Chem. Soc., 2013, 135, 3403-3406. *Featured in Chemical & Engineering News, 2013, 91, 29.
Moore, C. M.; Szymczak, N. K.*. 6,6'-Dihydroxy Terpyridine: A Proton-Responsive Bifunctional Ligand and its Application in Catalytic Transfer Hydrogenation of Ketones. Chem. Comm., 2013, 49 (4), 400 - 402
Carter, T. J.; Kampf, J. W.; Szymczak, N. K.*. Reduction of Borazines Mediated by Low-Valent Chromium Species. Angew. Ch., Int. Ed., 2012, 51, 13168-13172. *Featured in Advances in Engineering
Moore, C. M.; Szymczak, N. K.*. A tris(2-quinolylmethyl)amine Scaffold that Promotes Hydrogen Bonding within the Secondary Coordination Sphere. Dalton Trans., 2012, 41, 7886-7889. Invited contribution for ?New Talent: The Americas.?- *Top ten most accessed articles in May 2012