Mission statement:

To explore the application of transition metal catalysts in organic synthesis through mechanistic studies of important catalytic reactions, through the utilization of catalysts in selective transformations, and through the design of new ligands.

Research Interests

Transition metal catalysis plays a major role in organic synthesis. Catalysis enables the construction of important chemical bonds under mild conditions and in ways not possible using non-catalytic reactions. My research program is interested in developing a better understanding of the role of transition metal catalysts in chemo, regio and stereoselective organic transformations. This is accomplished in three ways: a) through mechanistic studies of important catalytic reactions, b) through utilization of catalysts in organic transformations and c) through synthesis of new ligands. The purpose for engaging in these studies is to improve the state of knowledge of the field of homogeneous catalysis. My efforts and those of my group will lead to the general improvement of important reactions as well as discovery of new catalytic applications. The project summaries below describe some of the exciting ongoing research projects in my group.

Asymmetric hydrogenation is one of the most important and most selective transition metal catalyzed reactions. However it is important to understand the factors that effect enantioselectivity. Recently we discovered a novel competing isomerization reaction that occurs during the hydrogenation of allylic alcohols. Our studies revealed that at low pressures of hydrogen gas, the allylic alcohol, geraniol, can isomerize to the homoallylic alcohol, gamma-geraniol.

We have shown that this isomerization directly affects enantioselectivity because with [(S)-BinapRuCl2]2NEt3 catalyst the gamma-geraniol intermediate is hydrogenated to the (S)-citronellol whereas (R)-citronellol is the major enantiomer obtained from geraniol. Thus, competition from the isomerization pathway directly affects the enantioselectivity of the asymmetric hydrogenation of geraniol. Currently, we are interested in studying the general affect of isomerization on enantioselectivity with other substrates and catalysts.

The above isomerization of an allylic alcohol to a homoallylic alcohol is an unusual transformation as the reaction product is less thermodynamically stable than the starting material. In addition, the reaction is highly regioselective. We are interested in learning more about the mechanism of this reaction. Preliminary investigations show that the structure of the BinapRuII catalyst and the methanol solvent is essential to the reaction. Moreover, we are interested in developing a way to make this reaction synthetically useful.

Our efforts in studying other metal catalyzed organic reactions include a Rh catalyzed asymmetric hydroboration of styrenes using a catalyst mixture that we have developed in our laboratory: IndenylRh(COD)/Binap/Catecholborane. We have shown that this catalyst mixture is effective for the regio and enantioselective hydroboration of styrenes. We have also developed a palladium catalyzed amination reaction for the selective synthesis of fluoroaniline derivatives.

In this reaction, we are able to substitute the halosubstituent (X = Cl, Br, I) in fluorohaloarenes with extremely high chemoselectivity. Future studies will involve the application of this reaction to prepare pharmaceutically important products.

To broaden the field of transition metal catalysis, it is important to develop new ligands with unique steric and electronic properties that will contribute to the reactivity and function of transition metal catalysis in new and novel ways. We have developed two new classes of ligands. The first set of ligands are the perfluoroalkyl cyclopentadiene and indene ligands. These contain the highly electron withdrawing perfluoroalkyl substituents and when the ligands are coordinated to a transition metal center, they dramatically increase the electrophilicity of the transition metal complex. Our goal is to use these ligands in catalytic transformations that traditionally require electophilic catalysts such as olefin polymerization.

The second set of ligands are a new class of chiral ligands called chiral annulated indenes. These are specially designed to incorporated three different structural units that can be systematically modified in order to fine-tune the reactivity of the catalyst. The ligands are prepared from enantiomerically pure bicyclic terpenes in 5 steps as shown for the verbenone derivative. The final step involves a novel application of the Nazarov cyclization reaction which is a stereospecific cyclization between a bicyclic terpene and an aromatic ring. Currently, we are developing methods to coordinate these ligands to transition metal centers in order to explore their application in asymmetric catalysis.