Allenes for Versatile Iron-Catalyzed C–H Activation by Weak O‑Coordination: Mechanistic Insights by Kinetics, Intermediate Isolation, and Computation

The iron-catalyzed hydroarylation of allenes was accomplished by weak phenone assistance. The C–H activation proceeded with excellent efficacy and high ortho-regioselectivity in proximity to the weakly coordinating carbonyl group for a range of substituted phenones and allenes. Detailed mechanistic studies, including the isolation of key intermediates, the structural characterization of an iron–metallacycle, and kinetic analysis, allowed the sound elucidation of a plausible catalytic working mode. This mechanistic rationale is supported by detailed computational density functional theory studies, which fully address multi-spin-state reactivity. Furthermore, in operando nuclear magnetic resonance monitoring of the catalytic reaction provided detailed insights into the mode of action of the iron-catalyzed C–H alkylation with allenes.