Pd-Catalyzed Cross-Coupling of Alkylzirconocenes and Aryl Chlorides

Comprehensive Summary Alkylzirconocenes, readily prepared by hydrozirconation of alkenes with Schwartz's reagent, are perspective yet rarely exploited partners in transition-metal catalyzed cross-coupling reaction. The notoriously low nucleophilicity of alkylzirconocenes and the potential beta-H elimination restrict their application in cross-coupling. Herein, we report the first Pd-catalyzed aryl-alkyl cross-coupling of alkylzirconocenes and aryl halides. A commercially available N-heterocyclic carbene (IPr) as the ligand for palladium catalyst is critical to enable the challenging process. This mild protocol does not require base additives and tolerates a broad scope of both coupling partners bearing various functional groups and heterocycles. Moreover, both terminal and internal alkenes are applicable, and the latter undergo "chain walking", giving the terminal coupling product exclusively. Preliminary mechanistic studies reveal a precatalyst activation pathway and inhibited beta-H elimination due to steric bulk of NHC ligand.