Chelating N-Heterocyclic Carbene Alkoxide as a Supporting Ligand for Pd~(ll/Iv) C-H Bond Functionalization Catalysis

摘要

Palladium(IV) complexes have been proposed as key intermediates in the catalytic ligand-directed functionalization of arene and alkane C-H bonds.1 The best current methods for CH halogenation reactions of this type employ Pd(OAc)_2 as a catalyst in conjunction with a terminal oxidant such as Phia_2 or an N-halosuccinimide. In the proposed Pd~(II)/Pd~(IV) cycle for these transformations, ligand-directed C-H activation (step a in Scheme 1) is followed by oxidation of Pd~(II) to Pd~(IV)in the presence of a strong oxidant (step b). The resulting Pd~(IV) complex can then undergo C-Cl bond-forming reductive elimination (step c) to generate the product.