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

• Published in: Journal of the American Chemical Society 2024-02, Vol.146 (6), p.4252-4259
• Main Authors: Gorgas, Nikolaus, Stadler, Benedek, White, Andrew J. P., Crimmin, Mark R.
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.3c14281

The oxidative addition of sp2 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 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 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.