Gorgas Nikolaus, Stadler Benedek, White Andrew J P, Crimmin Mark R
Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, 82 Wood Lane, Shepherds Bush, London W12 0BZ, U.K.
Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria.
J Am Chem Soc. 2024 Feb 14;146(6):4252-4259. doi: 10.1021/jacs.3c14281. Epub 2024 Feb 1.
The oxidative addition of sp 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 ()-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 an intramolecular sp 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 ()-selective phosphination of the employed styrenes.
烯烃的sp C-H键与单中心过渡金属配合物的氧化加成反应因C═C双键的竞争性π配位而变得复杂，限制了这类反应活性及后续应用的实例。在此，我们报道了一种结构明确的双金属Fe-Al配合物对苯乙烯的C-H活化反应。这些反应具有高度选择性，生成烯烃的（）-β-金属化产物。对于这个双金属体系，烯烃配位似乎是反应发生的必要条件。实验和计算结果表明了一种不寻常的反应途径，即（2 + 2）环加成中间体直接转化为氢化乙烯基产物——一种跨越两种金属的分子内sp C-H键活化反应。关键的C-H裂解步骤通过一个高度非同步的过渡态进行，该过渡态接近协同和分步机理边界，受芳基取代基的共振稳定能力影响。金属化烯烃可进一步官能化，这已通过所使用苯乙烯的（）-选择性膦化反应得到证明。
