Vinylic C–H Activation of Styrenes by an Iron–Aluminum Complex
Nikolaus Gorgas, Benedek Stadler, Andrew J. P. White, Mark R. Crimmin
Abstract
High Resolution Image Download MS PowerPoint Slide The oxidative addition of sp 2 C–H bonds of alkenes to single-site transition-metal complexes is complicated by the competing π-coordination of the C═C double bond, limiting the examples of this type of reactivity and onward 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 insights suggest an unusual reaction pathway in which a (2 + 2) cycloaddition intermediate is directly converted into the hydrido vinyl product via an intramolecular sp 2 C–H bond activation across the two metals. The key C–H cleavage step proceeds through a highly asynchronous transition state near the boundary between a concerted and a stepwise mechanism influenced by the resonance stabilization ability of the aryl substituent. The metalated alkenes can be further functionalized, which has been demonstrated by the ( E )-selective phosphination of the employed styrenes.