Bimolecular homolytic substitution (S_H2) is an open-shell mechanism that is implicated across a host of biochemical alkylation pathways. Surprisingly, however, this radical substitution manifold has not been generally deployed as a design element in synthetic C–C bond formation. Here, we demonstrate that the S_H2 mechanism can be leveraged to enable a biomimetic sp³-sp³ cross-coupling platform that furnishes quaternary sp³-carbon centers, a longstanding challenge in organic molecule construction. This heteroselective radical-radical coupling combines the capacity of iron porphyrin to readily distinguish between the S_H2 bond-forming roles of open-shell primary and tertiary carbons, and photocatalysis to generate both radical classes simultaneously from widely abundant functional groups. Mechanistic studies confirm the intermediacy of a primary alkyl–Fe(III) species prior to coupling and provide evidence for the S_H2 displacement pathway in the critical quaternary sp³-carbon bond formation step.

中文翻译：

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用于四元 sp3-碳形成的仿生 SH2 交叉偶联机制

双分子均裂取代 (S _H 2) 是一种开壳机制，涉及许多生化烷基化途径。然而，令人惊讶的是，这种自由基取代歧管通常没有被用作合成 C-C 键形成的设计元素。在这里，我们证明可以利用 S _H 2 机制来实现仿生 sp ³ -sp ³交叉偶联平台，该平台提供四元 sp ³ -碳中心，这是有机分子构建中的长期挑战。这种异质选择性自由基-自由基偶联结合了铁卟啉的能力，可以轻松区分 S _H2 开壳伯碳和叔碳的成键作用，以及从广泛丰富的官能团同时产生两种自由基的光催化作用。机理研究证实了初级烷基-Fe(III) 物质在偶联之前的中间体，并为关键的四元 sp ³ -碳键形成步骤中的 S _H 2 置换途径提供了证据。