Studies Directed toward the Improvement and Mechanistic Understanding of Several Transition Metal-Catalyzed Organic Reactions

Transition metals can be used to catalyze chemical reactions, allowing rapid and selective access to fine chemicals. The discovery of new reactions, as well as the improvement and understanding of existing reactions is thus a highly important task for organic chemists. Herein, work toward the improvement of a new transition metal-catalyzed reaction as well as work toward improving and understanding some existing transition metal-catalyzed transformations is described.

The mechanism of the Ir-catalyzed asymmetric hydrogenation of prochiral imines has been investigated for an experimentally relevant ligand-substrate combination using DFT calculations. The hydrogenation was found to proceed by an outer sphere pathway with an iridacyclic active catalyst species. Studies on the optimization, scope, and mechanism of a Ni-catalyzed α,β’-coupling of ketone enolates are also described. While the method does not appear to be very general or high yielding, an awareness of the conditions under which it occurs and the nuances of mechanism which lead to the ketone coupling product over the expected α-alkenylation product are important. These studies have been backed up by a more detailed study of the mechanism of the Ni-catalyzed α-alkenylation of ketone enolates using both experiments and calculations. A complementary study of the mechanism of a related Ni-catalyzed halogen exchange, proposed to accompany the alkenylation, is also described. While no specific mechanism can be concluded on as being operative at this time for either of these two reactions, significant progress has been made toward ruling out classical monometallic Ni-catalyzed pathways for both. Finally, computational work on understanding the rate acceleration and the role of a Rh catalyst in an asymmetric Giese radical addition to an alkene as well as work explaining the origin of stereoselectivity in a redox-relay Heck reaction is described.