Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA.
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan.
Nat Chem. 2020 Mar;12(3):276-283. doi: 10.1038/s41557-019-0409-4. Epub 2020 Feb 10.
Anti-Markovnikov additions to alkenes have been a longstanding goal of catalysis, and anti-Markovnikov addition of arenes to alkenes would produce alkylarenes that are distinct from those formed by acid-catalysed processes. Existing hydroarylations are either directed or occur with low reactivity and low regioselectivity for the n-alkylarene. Herein, we report the first undirected hydroarylation of unactivated alkenes with unactivated arenes that occurs with high regioselectivity for the anti-Markovnikov product. The reaction occurs with a nickel catalyst ligated by a highly sterically hindered N-heterocyclic carbene. Catalytically relevant arene- and alkene-bound nickel complexes have been characterized, and the rate-limiting step was shown to be reductive elimination to form the C-C bond. Density functional theory calculations, combined with second-generation absolutely localized molecular orbital energy decomposition analysis, suggest that the difference in activity between catalysts containing large and small carbenes results more from stabilizing intramolecular non-covalent interactions in the secondary coordination sphere than from steric hindrance.
反马氏加成一直是催化领域的一个长期目标，而芳烃与烯烃的反马氏加成将产生不同于酸催化过程形成的烷基芳烃。现有的氢芳基化反应要么是定向的，要么是活性低，对位烷基芳烃的区域选择性低。本文报道了首例未活化烯烃与未活化芳烃的无定向氢芳基化反应，该反应对位烷基芳烃的反马氏加成产物具有高区域选择性。该反应使用镍催化剂，由高度空间位阻的 N-杂环卡宾配位。已对与催化相关的芳烃和烯烃配位镍配合物进行了表征，反应的速控步骤被证明是还原消除形成 C-C 键。密度泛函理论计算结合第二代绝对局域分子轨道能量分解分析表明，大位阻和小位阻卡宾配体的催化剂之间的活性差异主要来自于次级配位球中稳定的分子内非共价相互作用，而不是空间位阻。
