Ni/NHC catalysis in C–H functionalization using air-tolerant nickelocene and sodium formate for in situ catalyst generation

Abstract

C–H functionalization in the area of fine organic synthesis is dominated by noble metal catalysts, which represent the most expensive and least sustainable options. Sustainable C–H functionalization may involve Ni catalysts. However, Ni(0) complexes are unstable under regular conditions and are more difficult to obtain as compared to Pd(0) or Rh(I). In the present study, a facile method for Ni⁰/NHC-catalyzed C–H alkylation and alkenylation of heteroarenes with alkenes and internal alkynes is presented. This method relies on the in situ generation of Ni⁰/NHC complexes from air-tolerant bench-stable precursors, Ni(Cp)₂, NHC·HCl salts and sodium formate. The optimized catalytic system demonstrates broad substrate scope and high selectivity (>60 products were obtained in up to 99% isolated yield). The approach represents a user-friendly alternative for air-sensitive and labile (NHC)Ni⁰ and Ni(COD)₂ precatalysts or complexes. The intermediates involved in the catalytic system were investigated and possible decomposition routes were mapped with NMR and ESI-MS. Rational control over the catalyst decomposition pathways further strengthens the sustainability of the procedure.