This review analyzes recent mechanistic studies that have provided new insights into how the structure of a metal complex influences the rate and selectivity of base-assisted C−H cleavage. Partitioning a broader mechanistic continuum into classes delimited by the polarization between catalyst and substrate during C−H cleavage is postulated as a method to identify catalysts favoring electrophilic or nucleophilic reactivity patterns, which may be predictive based on structural features of the metal complex (i. e., oxidation state, d-electron count, charge). Multi-metallic cooperativity and polynuclear speciation also provide new avenues to affect energy barriers for C−H cleavage and site selectivity beyond the limitations of single metal catalysts. An improved understanding of mechanistic nuances and structure-activity relationships on this important bond activation step carries important implications for efficiency and controllable site selectivity in non-directed C−H functionalization.
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