Catalytic Functionalization of Unsaturated Hydrocarbons

The focus of research in the Schmidt Group is the design and investigation of improved homogeneous catalysts for the functionalization of alkenes and alkynes. Specifically, three reaction classes are targeted: the hydroamination and hydrosilylation of alkenes and alkynes, olefin metathesis of alkenes with pendant reactive functionality, and the polymerization of functionalized alkenes. Through the development of enhanced organometallic catalysts for these reactions, we are working towards expanding substrate amenability, as well as providing useful synthetic pathways applicable to pharmaceutical and fine-chemicals production.

Ligand Design

An important aspect of organometallic catalyst development is the design of new ligand systems to support active metal centers. Our research focuses on ligands that can be synthesized using short (1 - 3 step), high-yielding, and large-scale synthetic schemes. We are also targeting ligand scaffolds that allow for the incorporation of a wide array of steric and electronic modifications. This enables the reactivity of the subsequent metal complexes to be easily tuned. Large ligand libraries provide for a plethora of metal complexes, which can then be combinatorially screened for catalytic activity. In addition, we are incorporating chiral components into ligand frameworks for pursuits in asymmetric catalysis.

Early Metal Catalysis

The use of early metal organometallic complexes as catalysts for reactions with alkenes is well documented. For example, the polymerization of ethylene and propylene can be achieved using titanium and zirconium metallocene catalysts. Additionally, early metal species have shown limited utility in the hydrosilylation and hydroamination of alkenes. These reactions are desired industrially as a means for the inexpensive functionalization of vast stores of ethylene and propylene. Hydroamination of selected alkenes can also lead to pharmaceutical derivatives, as amines are frequently the active functionality in these compounds. Our goal is to develop highly active and selective hydroamination catalysts capable of both the functionalization of commodity chemicals and the synthesis of natural products and pharmaceuticals.

To date, vinyl esters, amides, and ethers have proven to be difficult substrates for olefin metathesis catalysts. In an effort to achieve functionalized alkenes via this reaction pathway, early metal alkylidenes tailored to these substrates are being screened in our group as olefin metathesis catalysts. These complexes offer an alternative to the molybdenum and ruthenium catalysts that show little or no activity with these challenging substrates. The product functionalized alkenes can then be applied as substrates for hydroamination or hydrosilylation, yielding a multi-step catalytic synthesis of complex molecules.

Late Metal Catalysis
Complexation of a-diimine ligands with late metals has resulted in the discovery of ethylene polymerization catalysts capable of making highly branched polyethylene. Although numerous alkene polymerization catalysts are known, few are capable of tolerating functionalized olefins, with most catalysts limited to only ethylene and propylene as substrates. We are investigating late metal complexes using ligand sets designed specifically for the goal of polymerization of alkenes with pendant reactive functionality. Additionally, these catalysts are being employed in the ring-opening polymerization of halogenated lactones, substrates that have proven difficult for present zinc-based systems. Polyesters formed from these compounds are desirable due to their low permeability, high strength, and biodegradability.