Carbon-hydrogen (C-H) bond activation at PdIV: a Frontier in C-H functionalization catalysis

The direct functionalization of carbon-hydrogen (C-H) bonds has emerged as a versatile strategy for the synthesis and derivatization of organic molecules. Among the methods for C-H bond activation, catalytic processes that utilize a Pd-II/Pd-IV redox cycle are increasingly common. The C-H activation step in most of these catalytic cycles is thought to occur at a Pd-II centre. However, a number of recent reports have suggested the feasibility of C-H cleavage occurring at Pd-IV complexes. Importantly, these latter processes often result in complementary reactivity and selectivity relative to analogous transformations at Pd-II. This mini review highlights proposed examples of C-H activation at Pd-IV centres. Applications of this transformation in catalysis as well as mechanistic details obtained from stoichiometric model studies are discussed. Furthermore, challenges and future perspectives for the field are reviewed.