The Chemistry Department is located in the Merkert Chemistry Center, a 109,000 square foot structure designed to empower the dynamic, cutting-edge research for which the department is internationally recognized. The Merkert Chemistry Center contains faculty research laboratories in organic chemistry, chemical biology, and physical chemistry; specialized research facilities and shared instrumentation; and classrooms and teaching laboratories.
08.01.2018 Masayuki Wasa: C–H Functionalization of Amines via Alkene-Derived Nucleophiles through Cooperative Action of Chiral and Achiral Lewis Acid Catalysts: Applications in Enantioselective Synthesis
07.27.2017 Amir Hoveyda: “In Situ Methylene Capping: A General Strategy for Efficient Stereoretentive Catalytic Olefin Metathesis. The Concept, Methodological Implications, and Applications to Synthesis of Biologically Active Compounds”
By means of quantum chemical calculations Professor Haeffner has examined the molecular mechanisms underlying a novel transition-metal- free diboration reaction of olefins. The computational study shows that the reaction can proceed via four distinctively different non-concerted pathways A, B, C and D depending on which diboration reagent is being used. These new insights may guide further method development of this important chemical transformation. Shown below are the energetically favored transition structures along these pathways controlling the stereochemistry of the highly stereoselective SYN-diboration reaction between B 2 pin 2 and propene.
Read the article in Computational and Theoretical Chemistry.
As an electrochemical energy storage technology that holds the highest theoretical energy density, Li-O 2 batteries have been studied for over two decades. Its reported performance, however, remains much lower than expected. An important reason for the slow progress is the lack of stable electrolytes. Because of the high reactivity of oxygen species in the system, no known organic electrolytes meet the stability requirements. The search for a suitable electrolyte system remains an outstanding challenge in Li-O 2 battery research. To correct the deficiency, Professor Dunwei Wang and his team show that the issue can be solved with the use of a water-in-salt electrolyte system that involves no organic solvents. In essence, the electrolyte consists of super-concentrated LiTFSI (21 molality of lithium bis(trifluoromethanesulfonyl)imide), in which H 2 O molecules are locked to the ions and exhibit little reactivity toward the desired discharge product Li 2 O 2 or other oxygen species. Both qualitative and quantitative product analyses support that no measurable by-products form in the WiS system. With a carbon cathode, greatly improved cyclability of over 70 cycles can be obtained with WiS electrolyte in comparison with organic electrolytes. When the carbon cathode is replaced with a stable carbon-free material Ru/TiSi 2 , up to 300 cycles of Li-O 2 battery operations are obtained. This result sets a new benchmark in Li-O 2 battery performance with quantitative product detection. It also sets the stage for future optimizations to realize the full potential held by Li-O 2 batteries as a stable, high-capacity electrochemical energy storage technology.
Featured in Chem, Volume 4.
Radical cyclization represents a powerful strategy for construction of ring structures. Traditional radical cyclization, which is based on radical addition as the key step, necessitates the use of unsaturated substrates. As the latest synthetic application of metalloradical catalysis (MRC), the research laboratory of Professor Peter Zhang, led by graduate students Yong Wang and Xin Wen, has demonstrated a different mode of radical cyclization that can employ saturated C–H substrates. They have developed a new Co(II)-based metalloradical system that can catalytically activate aliphatic diazo compounds for enantioselective radical alkylation of various C(sp 3 )–H bonds, allowing for efficient construction of chiral pyrrolidines and other valuable 5-membered compounds. In addition to chemoselectivity and regioselectivity, this new radical cyclization features functional group tolerance and heteroarene compatibility. This alternative strategy of radical cyclization provides a new retrosynthetic paradigm to prepare five-membered cyclic molecules from readily available linear aldehydes through the union of C–H and C=O elements for C–C bond formation.
Read the article in Journal of the American Chemical Society.
The Wang group has led an international collaboration in the development of a new heterogeneous catalyst for solar water splitting applications. The catalyst consists of two Ir atoms as the active site. It represents one of the first examples of such catalysts with well-defined atomic structures. Most other high-performance heterogeneous catalysts are poorly defined in their active centers. To correct the deficiency, graduate student Yanyan Zhao from the Wang group started from an Ir molecular catalyst ([Ir(pyalc)(H2O)2(μ-O)]22+ homo-dimer) and immobilize it onto Fe2O3 surface. A subsequent photochemical treatment was found to strip off all organic ligands to yield the Ir-O- Ir dimer that are stabilized by only H2O, OH - and surface O. To study the structures, the authors employed a suite of characterization tools, including aberration-corrected TEM, X-ray absorption spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy. The unique structure was unambiguously confirmed. Importantly, the Ir-O- Ir catalyst exhibited high activity toward solar water oxidation. The well-defined structure allowed the authors to propose the reaction mechanisms, which were confirmed by DFT calculations. A new door to heterogeneous catalyst preparation and study that can directly benefit from knowledge gained on homogeneous catalysis is opened up. The study also involved Yale University, Tufts University, University of California Irvine, the Advanced Light Source, Tsinghua University and Nanjing University.
Efficient catalytic reactions that generate C–C bonds enantioselectively and those that produce trisubstituted alkenes diastereoselectively are central to research in modern chemistry. Transformations that accomplish these tasks simultaneously in a single operation are scarce and highly prized; this is particularly the case if the catalysts, substrates and reagents are easily accessed at low cost and reactions are simple to set and conditions are conditions are mild. In an Article in this week’s issue of Nature, Professor Amir Hoveyda and graduate students Fanke Meng and Kevin McGrath report a facile multicomponent catalytic process that begins with a chemo-, site- and diastereoselective copper–boron addition to a monosubstituted allene. The resulting boron-substituted organocopper intermediates then participate in a chemo-, site- and enantioselective allylic substitution. Products, which contain a stereogenic carbon center, a mono-substituted alkene and an easily modifiable Z-trisubstituted alkenylboron group, are obtained in up to 89% yield, with >98% branch- and stereoselectivity and >99:1 enantiomeric ratio. The copper-based catalyst is derived from a robust heterocyclic salt that can be prepared in multi-gram quantities from inexpensive starting materials and without costly purification procedures. Utility of the approach is showcased through exceptionally concise enantioselective synthesis of gram quantities of natural products rottnestol (member of an antibiotic family) and herboxidiene (anti-tumor). In the case of rottnestol, the overall yield is seven times better than the best formerly reported approach, and herboxidiene is accessed in nearly twice the total yield of the most efficient previous route.
The transcription factor p53 commences arrest of the natural cell cycle in response to DNA damage. The p53 peptide, like other short peptide segments of a protein, is found to be in disordered states in solution and therefore is not able to maintain proper interactions for binding. Stabilization of the 16-residue helical domain in p53 was previously accomplished by introducing an all-hydrocarbon tether of different lengths and stereochemistry. This stapled version of the p53 peptide was shown to slow the growth of cancer cells in vivo by activating the p53-mediated apoptotic paths.