Homogeneous, Supramolecular and Bio-Inspired Catalysis (HomKat) group, Van 't Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Amsterdam, The Netherlands.
Nat Chem. 2022 May;14(5):550-557. doi: 10.1038/s41557-022-00905-4. Epub 2022 Mar 24.
Square-planar cobalt(II) systems have emerged as powerful carbene transfer catalysts for the synthesis of numerous (hetero)cyclic compounds via cobalt(III)-carbene radical intermediates. Spectroscopic detection and characterization of reactive carbene radical intermediates is limited to a few scattered experiments, centered around monosubstituted carbenes. Here, we reveal the formation of disubstituted cobalt(III)-carbene radicals derived from a cobalt(II)-tetraphenylporphyrin complex and acceptor-acceptor λ-iodaneylidenes (iodonium ylides) as carbene precursors and their catalytic application. Iodonium ylides generate biscarbenoid species via reversible ligand modification of the paramagnetic cobalt(II)-tetraphenylporphyrin complex catalyst. Two interconnected catalytic cycles are involved in the overall mechanism, with a monocarbene radical and an N-enolate-carbene radical intermediate at the heart of each respective cycle. Notably, N-enolate formation is not a deactivation pathway but a reversible process, enabling transfer of two carbene moieties from a single N-enolate-carbene radical intermediate. The findings are supported by extensive experimental and computational studies.
平面正方形钴(II)配合物已成为通过钴(III)-卡宾自由基中间体合成众多（杂）环化合物的有力卡宾转移催化剂。活性卡宾自由基中间体的光谱检测和表征仅限于少数分散的实验，主要集中在单取代卡宾上。在这里，我们揭示了由钴(II)-四苯基卟啉配合物和受体-受体 λ-碘酰基（碘翁）作为卡宾前体制备的双取代钴(III)-卡宾自由基的形成及其催化应用。碘翁通过顺磁钴(II)-四苯基卟啉配合物催化剂的可逆配体修饰生成双卡宾物种。整个机理涉及两个相互关联的催化循环，每个循环的核心都是单卡宾自由基和 N-烯醇化物-卡宾自由基中间体。值得注意的是，N-烯醇化物的形成不是失活途径，而是一个可逆过程，能够从单个 N-烯醇化物-卡宾自由基中间体中转移两个卡宾部分。这些发现得到了广泛的实验和计算研究的支持。
