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.