Our research aims to discover, develop and understand new transition metal-catalyzed reactions. The scope of our studies ranges from catalytic aromatic substitution to the functionalization of alkanes to the enantioselective formation of C-N and C-O bonds in amines and ethers. The discovery of fundamentally new transition metal chemistry and its development into practical, catalytic synthetic methods is a theme of our research. We reach these goals by obtaining insight from detailed mechanistic studies. The following classes of metal-catalyzed reactions are currently being investigated in my group:

Catalytic Formation of Amines, Ethers and Sulfides.

We developed a palladium-catalyzed process that forms arylamines, aryl sulfides, and arylethers. The catalytic chemistry resulted from our detailed mechanistic experiments on transition metal amide, alkoxo and thiolato complexes. Our most recently developed catalyst leads to the formation of arylamines and aryl sulfides with turnover numbers exceeding 10,000 in many cases and ppm levels of palladium in others.

This catalysis is useful for total synthesis, combinatorial synthesis, and the preparation of electronically important organic materials. At the same time, the catalysis involves unprecedented reactions of transition metal compounds. Thus, some students focus on novel inorganic chemistry while others use this reaction as a modular route to nitrogen heterocycles and polyanilines.

See our publications on methodology development and reaction mechanism of catalytic C-X bond formation.

Catalytic Alpha Arylation of Carbonyl Compounds.

We have developed a simple method to convert aryl halides and ketones, esters, amides, cyanoesters, malonates, nitriles, and related compounds to alpha aryl carbonyl compounds and nitriles in the presence of base and a palladium catalyst. Familiar compounds that can be generated from these products include Ibuprofen, Naproxin and Tamoxifen. The reaction occurs in a general fashion and in many cases with low catalyst loadings.

As part of our studies to understand this process, we have generated both O-bound and C-bound palladium enolate complexes. These complexes undergo reductive elimination of the alpha-aryl ketone, ester, or amide product in good yields. Studies on the effects of changing the enolate electronics on reductive elimination rate are in progress.

See our publications on methodology development and reaction mechanism of catalytic C-C bond formation.

Transition Metal Boryl- and Borane Complexes. Catalytic, Regiospecific Functionalization of Alkanes

The chemistry of compounds with covalent transition metals and main group bonds is unexplored. While studying this fundamental reactivity, we discovered that metal boryl compounds react with arenes and alkanes to form functionalized products. Most recently, we have developed a regiospecific functionalization of alkanes using borane or diboron reagents in the presence of a rhodium catalyst and a sterecally controlled, iridium-catalyzed functionalization of arenes using the same boron reagents. We are currently exploring improved catalysts, as well as the scope and applications of the functionalization process.

Our mechanistic work on this process has intersected with our fundamental work in the group on borane sigma complexes. These complexes have unusual bonding between a metal hydride and the boryl ligand. In these complexes a partial, intact B-H bond accompanies an M-H and M-B bond. Recently, we have found that complexes of this type are similar to those involved in the alkane functionalization process.

See our publications on main group-transition metal organometallics and catalytic C-H bond activation.

Olefin Hydroamination

The hydroamination of olefins is a long-standing goal for transition metal catalysis. We have recently discovered catalysts for the addition of aromatic and aliphatic amines to dienes and vinylarenes. We have shown that the proper selection of catalysts allows for the selective formation of either Markovnikov or anti-Markovnikov products. In addition to observing faster rates, higher turnover frequencies, and broader scope for such reactions than had been obtained previously, we have uncovered conditions to catalyze examples of these reactions with good enantioselectivity. We are currently striving to expand the scope of these reactions and to conduct detailed mechanistic studies on both processes.

See our publications on amination of olefins .

Enantioselective Allylic Amination and Etherification

We have recently reported a method to form chiral allylic amines and ethers in high enantiomeric excess from terminal allylic carbonates with an iridium catalyst. Most recently, we have begun to undertake mechanistic studies to determine the identity of the true catalyst. These studies have led to an iridium complex that catalyzes the reactions of a variety of heteroatom nucleophiles with broad scope to form amines and ethers rapidly at room temperature with high regio and enantioselectivity. Further, these studies led to a simplified version of this catalyst that contains one phenethyl group as the only resolved stereochemical element of the catalyst.

See our publications on iridium-catalyzed allylic substitution.

Combinatorial Catalyst Discovery

We have been developing alternative approaches to the conventional methods for catalyst discovery and development. In particular, we have been using fluorescent and colorimetric assays to evaluate catalysts for carbon-carbon and carbon-nitrogen bond forming processes catalyzed by transition metal complexes. With this approach, we recently discovered the catalysts for hydroamination of substrates with C=C bonds discussed above and for several types of room temperature cross-coupling reactions.

See our publications on high-throughput screening.