Ligand Control in Selective C-H Oxidative Functionalization Using Pd-PEPPSI-Type Complexes

To achieve high selectivity in directed C-H activation, an NHC ligand was introduced to a palladium catalyst. A range of Pd-PEPPSI complexes were applied in the direct acetoxylation of 2-phenylpyridine. The best catalyst was found to be the one based on a diisopropylphenyl-substituted NHC ligand, and this was successfully used for the functionalization of sp(2) as well as more challenging sp(3) bonds for a broad variety of substrates. The explored method showed a highly improved selectivity compared to previously reported results with up to 96 % yield for the monoacetoxylated product. Kinetic studies show that sterics of the catalyst is less important in dictating conversion and selectivity; despite an induction period, it was shown that the catalyst is molecular in nature.