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Amanda Jones' Research
Much of the power of chemistry lies in our ability to efficiently manipulate reagents to construct complex molecules with desired structural features. Such synthetic molecules are sought for a variety of reasons including novel drug and materials development. Mechanistic chemistry itself relies on the ability to prepare substrates for analysis. Synthetic targets serve as a driving force for the continued improvement of current methodologies, and in turn, synthetic methodologies often find application in targets for which they were not specifically designed. At the heart of this synergy, is a mechanistic understanding of reactions, which facilitates reaction optimization and application. NMR spectroscopy is a powerful tool, because of the breadth of detailed structural information it can provide and its conceptual simplicity. In addition to standard kinetics experiments, research in my lab will focus on the use of heteronuclear (e.g. 19F, 31P, 6Li, 7Li), variable temperature NMR spectroscopy to elucidate the structure and reactivity of reagents used in synthetic chemistry. Three areas of initial study are outlined below. Additionally, rapid-injection NMR (RINMR) spectroscopy has proven to be a highly useful technology for observing fast reactions, and I foresee opportunities in each project to use RINMR. We will work to design an appropriate RINMR apparatus for use with the Wake Forest department’s 500 MHz spectrometer.
Homogeneous Gold Catalysis. Homogeneous gold catalysis is emerging as an exciting method for the activation of double and triple bonds. Methodology publications are emerging at an astonishing rate, whereas studies specifically aimed at elucidating the mechanism of these processes lags behind. An understanding of the distinct roles of gold and proton catalysis is still developing. Work in this area will seek to explore the dynamic and kinetic aspects of elementary steps in gold catalyzed reactions that have found use in organic synthesis. Conditions will be explored that are proposed to allow gold intermediates to be observed in situ. The evolution of organic and inorganic intermediates will be monitored to determine the differing contributions from gold and proton catalysis. As models of the postulated individual steps, discrete alkyl and vinyl gold complexes will be prepared and their reactivity toward protons examined. These studies will aid in the understanding of factors that govern selectivity and efficiency in gold-catalyzed transformations.
Reactivity Studies and Solution Characterization of Mixed Organolithium / Organozinc Reagents. There has been a recent increase in interest in bimetallic reagents due to a “mixed metal synergy” that leads to enhanced reactivity and selectivity compared to either monometallic reagent acting alone. Representative of this type of reagent are the “lithium organozincates” resulting from a combination of organolithium and organozinc reagents. Although they are frequently depicted as separated ion pairs, the solution structures of these reagents are not fully understood, nor is the reason for their unique observed reactivity. The very polar lithium–coordinating co-solvent hexamethylphosphoramide (HMPA) [O=P(NMe2)3] will be used as a structure probe to determine the extent of ion pairing in solution. It will also be used as a reactivity probe, since the presence of HMPA has been shown to have kinetic effects on carbanion reactivity that can be correlated with its effect on the extent of ion-pairing in solution.
Reactivity and Structural Studies of Conjugated Titanium Carbenes. To appreciate the importance of metal carbene complexes in chemistry, one need look no further than the advancement and understanding of olefin metathesis. The introduction of a double bond “in conjugation” with the metal-carbon double bond results in an increase in the available modes of bonding and reactivity. For example, vinyl titanium carbenes exhibit reactivity that can be rationalized based on either ring-opened carbene structures or closed titanacyclobutene structures. We will use low-temperature NMR spectroscopy to explore the structure and formation of vinyl titanium carbenes. An additional structural aspect that will be explored using titanium benzylidene complexes is the extent of conjugation between the titanium-carbon double bond and a carbon-carbon double bond. Results from these studies may lead to improvements in selectivity and the utility of these reagents as synthetic tools. They may also provide fundamental and general insight into the structure and reactivity of vinyl metal carbenes.
Reich, H. J.; Sikorski, W. H.; Sanders, A. W.; Jones, A. C.; Plessel, K. N. Multinuclear NMR Study of the Solution Structure and Reactivity of Tris(trimethylsilyl)methyllithium and its Iodine Ate Complex. J. Org. Chem. 2009, 74, 719–729.
Jones, A. C.; Sanders, A. W.; Sikorski, W. H.; Jansen, K. L.; Reich, H. J. Reactivity of the Triple Ion and Separated Ion Pair of Tris(trimethylsilyl)methyllithium with Aldehydes: A RINMR Study. J. Am. Chem. Soc. 2008, 130, 6060–6061.
Jones, A. C.; Sanders, A. W.; Bevan, M. J., Reich, H. J. Reactivity of Individual Organolithium Aggregates – a RINMR Study of n-Butyllithium and 2-Methoxy-6-(methoxymethyl)phenyllithium. J. Am. Chem. Soc. 2007, 129, 3492–3493.
Reich, H. J.; Sikorski, W. H.; Thompson, J. L.; Sanders, A. W.; Jones, A. C. Interconversion of Contact and Separated Ion Pairs in Silyl- and Arylthio-Substituted Alkyllithium Reagents. Org. Lett. 2006, 8, 4003–4006.
Bradley, A. Z.; Cohen, A. D.; Jones, A. C.; Ho, D. M.; Jones, M., Jr. Photolysis of Naphthocarborane and Benzocarborane in Oxygen. Tetrahedron Lett. 2000, 41, 8695–8698.