Organic Chemistry Seminar
Nickel catalysts exhibit unique properties. Open-shell configurations are relatively stable and readily accessible, which lead to radical pathways. Moreover, the reduction potential of Ni is considerably lower than that of Pd. This reactivity is employed to functionalize alkenes. Enantioselective 1,2-dicarbofunctionalization of alkenes accesses molecules with intricate substitution patterns while introducing stereocenters. This method is readily applicable to prepare molecules with important bioactivity, such as a,a,b-triarylated ethane scaffolds. The use of reducing conditions with alkyl and aryl halides as the coupling partners avoids stoichiometric organometallic reagents and tolerates a broad range of functional groups. Mechanistic studies reveal that the use of Ni catalysts initiates radical formation and leads to unconventional enantio-determining steps. A two-electron redox pathway taking place on a Ni(I)/Ni(III) platform achieves trans-selective diene coupling to afford important cyclic structures.