PROF. TIMOTHY B. CLARK

Research Interests 

My research interests are in the applications of organometallic chemistry to organic synthesis. Organometallic complexes are used as catalysts to mediate organic reactions that either cannot be achieved without a metal, or are much more efficient and practical with the metal present. The goals of my research are to develop new catalysts that are synthetically useful and ultimately to apply the newly developed reaction to a synthetic target. Projects in my group range from synthetic organometallic chemistry (design of new transition metal complexes) to new organic reaction development using transition metal catalysts.
 

Directed C-H Functionalization

The development of methods that convert carbon-hydrogen bonds to carbon-carbon, or carbon-heteroatom bonds, is currently a major synthetic challenge. Arene and alkane terminal C-H functionalization (C-H bond to C-X bond) with metal boryl complexes is one solution to this ongoing problem. The newly formed carbonboron bond in the product is easily converted into synthetically relevant substrates through coupling reactions, oxidation/amination, and several other transformations. This research project is directed toward expanding C-H functionalization with metal boryl complexes using boron analogs of the Shvo hydrogenation catalyst (Scheme 1, 1). The acidic proton of the hydroxycyclopentadienyl ligand is used to direct C-H borylation of heteroatom-substituted organic substrates. Simple directing groups, such as those present in ethers, thioethers, amines, and carbonyl compounds should lead to high selectivity in directed C-H functionalization. Ultimately, conditions for catalytic C-H borylation will be investigated.

Asymmetric Dearomatization Reactions Utilizing h²-Rhenium p-bases to Provide Highly Functionalized Carbocycles

Metal-mediated dearomatization reactions, using a metal p-base, constitute a powerful strategy for the conversion of common aromatic starting materials to synthetically valuable carbocycles and heterocycles. The current methodology is limited due to the use of highly electrophilic reagents for the initial dearomatization step. Our group is developing a method to obviate the use of strongly electrophilic reagents by inducing the initial dearomatization step with the displacement of an exocyclic benzylic leaving group. The interaction of a rhenium p-base with the remaining p-system of the arene will facilitate the elimination of the leaving group. The reactivity of the resulting p-quinone methide-type intermediate will be exploited through a number of tandem addition reactions. Ultimately, kinetic resolutions and dynamic kinetic asymmetric transformations will be used to provide enantioenriched carbocycles and heterocycles from racemic aromatic substrates.