Vinylic C–H Activation of Styrenes by an Iron–Aluminum Complex

The oxidative addition of sp2 C–H bonds of alkenes to single-site transition metal complexes is complicated by the compet-ing π-coordination of the C=C double bond, limiting the examples of this type of reactivity and onwards applications. Here we report the C–H activation of styrenes by a well-defined bimetallic Fe–Al complex. These reactions are highly selective resulting in the (E)-β-metalation of the alkene. For this bimetallic system, alkene binding appears to be essential for the reaction to occur. Experimental and computational insight suggests an unusual reaction pathway in which a (2+2) cycloaddi-tion intermediate is directly converted into the hydrido vinyl product via an intramolecular sp2 C–H bond activation across the two metals. The key C–H cleavage step proceeds through a highly asynchronous transition state near the boundary be-tween a concerted/stepwise mechanism influenced by the resonance stabilization ability of the aryl substituent.