Our group applies mechanistic principles to develop new concepts in catalysis. A particular focus is the development of organometallic and organic catalysts for the synthesis of complex macromolecular architectures. In organometallic catalysis, we investigate catalysts that can access multiple kinetic states during a polymerization reaction in order to control sequence distribution. We have devised a novel strategy for the synthesis of elastomeric polypropylene utilizing a metallocene catalyst whose structure was designed to interconvert between chiral and achiral coordination geometries on the timescale of the synthesis of a single polymer chain. We have also developed a novel method for the synthesis of alternating copolymers of ethylene and propylene by exploiting catalysts that can access multiple coordination sites that exhibit different kinetic selectivities towards the two monomers. In collaboration with Jim Hedrick of IBM laboratories, we have developed an extensive platform of organic catalysts for the controlled ring-opening polymerization of lactones. Mechanistic studies of nucleophilic N-heterocyclic carbene catalysts revealed an unusual zwitterionic mechanism which enabled the synthesis of high molecular weight cyclic polyesters, a novel topology for these biodegradable and biocompatible macromolecules. These efforts combine elements of mechanistic organic and organometallic chemistry, polymer synthesis, and homogeneous catalysis to rationally design new macromolecular structures.

1) "Zwitterionic Polymerization of Lactide to Cyclic Poly(lactide)s by using N-Heterocyclic Carbene Organocatalysts," D.A. Culkin, W. Jeong, S. Csihony, E.D. Gomez, J.L. Hedrick, N.P. Balsara, R.M. Waymouth Angew. Chem., Int. Ed.., 46 2627-2630 (2007).

2 "A Distinctive Organocatalytic Approach to Macromolecular Architectures,"O. Coulembier, M. Kiesewetter, A. Mason, P. Dubois, J.L. Hedrick, R.M. Waymouth, Angew. Chem., Int. Ed., 46, 4719-4721 (2007).

3 "Homolysis of Weak Ti-O Bonds: Experimental and Theoretical Studies of Titanium Oxygen Bonds Derived from Stable Nitroxyl Radicals," K-W Huang, J.H. Han, A.P. Cole, C.B. Musgrave, R.M. Waymouth, J. Am. Chem. Soc., 127, 3807-3816 (2005).

4"2-ArylIndene Metallocenes: Conformationally Dynamic Catalysts to Control the Structure and Properties of Polypropylene," S. Lin and R.M. Waymouth, Acc. Chem. Res., 35 (9), 765-773 (2002).

5 "Cyclocopolymerization: A Mechanistic Probe for Dual-Site Alternating Copolymerization of Ethylene and alpha-Olefins," T.N. Choo and R.M. Waymouth, J. Am. Chem. Soc., 124, 4188-4189 (2002).