The Bercaw Group is investigating the general area of organotransition metal chemistry. In particular, the research is focused on the edges of the transition metal block of the Periodic Table: the early transition metal chemistry (complexes of Sc, Y, Zr, Hf, Nb and Ta) and its applications to the Ziegler-Natta olefin polymerization and the late transition metal chemistry (complexes of Pd and Pt) relevant to alkane oxidation catalysis. New compounds are prepared using specialized vacuum line, Schlenk, and glove box techniques, and they are commonly characterized by multinuclear NMR spectrometry and by single crystal X-ray diffraction methods. Reaction mechanisms are studied by isotopic labeling, characterization of intermediates, dynamic NMR techniques, and monitoring of reaction kinetics and stereochemistry. These studies are ultimately directed toward assessing the roles of transition metals in catalysis and developing new stoichiometric and catalytic reactions for converting readily available molecules such as olefins and alkanes into more valuable products.

Early Transition Metal Chemistry

We have recently prepared a series of highly active Cs-symmetric olefin polymerization catalysts that polymerize propylene with unprecedented stereospecificities. The research in this area has been focused on the elucidation of the mechanism of olefin polymerization as well as on the use of the metallocene catalysts for stereoselective catalysis.

Several cationic alkyl-olefin zirconocene complexes were prepared as models of Ziegler-Natta polymerization catalysts. Two important steps of the olefin polymerization catalysis can be studied with the help of these and related models: olefin dissociation/coordination equilibria and olefin insertion into zirconium-carbon bond.

In view of the amazingly high activity of the doubly-bridged ansa-metallocene catalysts towards a-olefins, we anticipated that they might also ehxibit high reactivity towards 3-substitutes a-olefins with possible implications for the kinetic resolution of racemic 3- and 4-substituted a-olefins.

Late Transition Metal Chemistry

The activation of alkanes by organometallic species has attracted a lot of interest, since many examples of rapid reactions even at low temperatures have been found, with selectivity patterns quite different from those observed in free-radical reactions. We are investigating a promising organometallic system, one based on aqueous platinum halides originally reported by Shilov, that appears to escape the common constraints of incompatibility with oxidants and prohibitively large metal-oxygen bond strengths. We are pursuing the synthesis of robust electrophilic platinum(II) complexes capable of C–H activation reactions.

We are interested in studying the mechanism of the C–H activation step. In particular, we are investigating the influence of the steric and electronic factors on the reactivity and selectivity of electrophilic C–H activation in a-diimine-ligated platinum(II) complexes.

Attempts to introduce dioxygen as a stoichiometric oxidant into Shilov-type alkane oxidation processes is another area of research in the group. We have recently discovered that dialkylplatinum(II) complexes are oxidized by dioxygen to the platinum(IV) products. We are now trying to couple this step with the C–H activation reaction.

Last updated April 30, 2008. Questions? Suggestions? Raves? E-mail Web Czar