Homogeneous Catalysis

NHC elimination

NHCs as Non-innocent Ligands

The unprecedented activity of cross-coupling catalysts based on N-heterocyclic carbenes (NHCs) is usually ascribed to electronic properties; NHCs are otherwise regarded as mere spectator ligands. However, Cavell has shown that in solution they can readily undergo reductive elimination as imidazolium derivatives. Thus, low-coordinate transition-metal species are produced, which may alternatively explain the high activity of such catalyst systems. Using advanced ESI-MS/MS techniques, I measured the gas-phase barriers for reductive elimination vs ligand dissociation from a cationic NHC−palladium complex, as well as for fragmentation of the resulting π-complex. This system was quite challenging because it features competitive and sequential reaction channels that lead to the same final product (see right).

This research was published in Chemistry − A European Journal

Zirconocenium Polymerization

Industrial olefin polymerization often uses zirconocene precatalysts that are activated with aluminum or boron reagents. The resulting catalyst mixtures are generally ill-defined, although their composition critically determines polymerization activity and regioselectivity. I advised Déborah Mathis on part of her systematic investigations on the nature of the generated zirconocenium ion pairs, their dynamic interconversion, and their catalytic activity in ethylene polymerization.

Structure, Dynamics, and Polymerization Activity of Zirconocenium Ion Pairs Generated with Boron-C<SUB>6</SUB>F<SUB>5</SUB> Compounds and Al<SUB>2</SUB>R<SUB>6</SUB>

This research was published in Organometallics

Platinum C–C coupling and C–H activation

Platinum complexes exhibit promising reactivity for mild activation of methane to produce industrially more useful chemicals. The principal processes in such conversions are oxidative C–H bond activation and reductive C–C bond formation. Together with Ilia Kobylianskii, I combined advanced ESI-MS/MS techniques and high-level quantum-chemical calculations to determine the gas-phase barriers and accessible pathways for the formation of methane, ethane, and ethylene from a trimethylplatinum(IV) complex.

Gas-Phase Thermochemistry for Alkane Reductive Elimination from Pt(IV)

This research was recently published in Organometallics