Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.
Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea.
Nat Chem. 2018 Feb;10(2):218-224. doi: 10.1038/nchem.2900. Epub 2017 Dec 11.
Direct arylation of C-H bonds is in principle a powerful way of preparing value-added molecules that contain carbon-aryl fragments. Unfortunately, currently available synthetic methods are not sufficiently effective to be practical alternatives to conventional cross-coupling reactions. We propose that the main problem lies in the late portion of the catalytic cycle where reductive elimination gives the desired carbon-aryl bond. Accordingly, we have developed a strategy where the Ir(III) centre of the key intermediate is first oxidized to Ir(IV). Density functional theory calculations indicate that the barrier to reductive elimination is reduced by nearly 19 kcal mol for this oxidized complex compared with that of its Ir(III) counterpart. Various experiments confirm this prediction, affording a new methodology capable of directly arylating C-H bonds at room temperature with a broad substrate scope and in good yields. This work highlights how the oxidation states of intermediates can be targeted deliberately to catalyse an otherwise impossible reaction.
直接 C-H 芳基化从原则上讲是一种制备含碳芳基片段的增值分子的有效方法。不幸的是，目前可用的合成方法效率不够高，无法替代传统的交叉偶联反应。我们认为主要问题在于催化循环的后期部分，其中还原消除生成所需的碳-芳基键。因此，我们提出了一种策略，其中关键中间体的 Ir(III) 中心首先被氧化为 Ir(IV)。密度泛函理论计算表明，与 Ir(III) 对应物相比，该氧化配合物的还原消除势垒降低了近 19 kcal/mol。各种实验证实了这一预测，提供了一种新的方法，能够在室温下直接芳基化 C-H 键，具有广泛的底物范围和良好的收率。这项工作强调了如何有目的地针对中间体的氧化态来催化原本不可能的反应。
