NICKEL- AND COBALT-CATALYZED ASYMMETRIC HYDROFUNCTIONALIZATIONS OF ALKENES UTILIZING N-DONOR LIGANDS

Abstract

Hydrofunctionalizations are some of the most widely-used reactions and are highly applicable to the synthesis of commodity, fine, and pharmaceutical chemicals, among others. While the field is currently dominated by precious metals, namely iridium, ruthenium, and rhodium, they are costly and toxic. Earth-abundant metals, on the other hand, are cheap, non-toxic, and offer the potential for new reactivity. N-donor ligands also offer an inexpensive, easily accessible alternative to the popular phosphine ligands. In this work, four C2-symmetric diimines, one C1-symmetric diimine, and two chiral N-heterocyclic carbenes (NHCs) were successfully synthesized along with five indenes and two dialins as substrates. As the diimines initially showed low enantioselectivities in both the hydroboration and hydrogenation reactions, a library of N-donor ligands was obtained to be evaluated. Reactions were run from stock solution the asymmetric hydroboration of styrene, 3-phenyl-1H-indene, and 2,3-dimethyl-1-butene and analyzed by GC and chiral GC. With 0.5 mmol scale reactions, low yields to 3-phenylindane and percent conversions of styrene were found along with a best enantioselectivity of 10. Attempts to improve activity by changing reaction conditions such as solvent, temperature, and molarity only gave modest improvements. The diimine ligands were also evaluated for the asymmetric hydrogenation of 4-methyl-1,2-dihydronaphthalene for which they gave excellent NMR yields upwards of 95%, however, enantioinduction was again low. Stoichiometric experiments to identify the catalytically active species or form crystalline samples for X-ray crystallography were unsuccessful. Overall, though the reactivity shown by ligands is scattered, this thesis identifies cobalt as a favored metal precursor for styrene hydroboration and nickel for 3-phenyl-1H-indene hydroboration.