Decomposition of aryl and unsubstituted diazo ester into Rh(II)‐carbenes by the [(IMes)Rh2(OAc)4] complex is shown to be slower than with Rh2(OAc)4. Diazo esters substituted by a second electron‐withdrawing group do not suffer nitrogen extrusion when exposed for several hours to this Rh(II)·NHC complex at room temperature. This chemoselective decomposition of diazo esters depending on their substituent (Ar, H, EWG) can furthermore be achieved on a mixture of substrates. The catalytic activity of [(IMes)Rh2(OAc)4] towards electron‐poor diazo compounds is restored by heating to reflux in chloroform, or after decomplexation of the NHC by addition of GaCl3. Following these findings, the [(IMes)Rh2(OAc)4] complex was used to induce a fully selective reaction cascade from a mixture of two diazo esters. First, a donor/acceptor diazo compound was decomposed selectively at room temperature to give an intermolecular O‐H insertion product without any decomposition of the electron poor diazo compound. Addition of GaGl3 then triggered nitrogen extrusion from the diazo malonate to give a 1,5‐C‐H insertion product. This transformation, where decomposition of diazo compounds catalyzed by Rh(II) complexes can be externally controlled, represents the first example of assisted tandem catalysis with two metal carbene precursors.

中文翻译：

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[(IMes)Rh2(OAc)4] 配合物对重氮酯的化学选择性和触发分解：重氮化合物混合物的辅助串联催化过程


[(IMes)Rh2(OAc)4] 络合物将芳基和未取代的重氮酯分解为 Rh(II)-卡宾，其分解速度比 Rh2(OAc)4 慢。当在室温下暴露于该 Rh(II)·NHC 络合物数小时时，被第二个吸电子基团取代的重氮酯不会受到氮挤出。此外，重氮酯的这种化学选择性分解取决于其取代基（Ar、H、EWG），可以在底物混合物上实现。 [(IMes)Rh2(OAc)4] 对缺电子重氮化合物的催化活性可以通过在氯仿中加热回流或通过添加 GaCl3 对 NHC 解络后恢复。根据这些发现，[(IMes)Rh2(OAc)4]复合物被用来诱导两种重氮酯的混合物发生完全选择性的级联反应。首先，供体/受体重氮化合物在室温下选择性分解，得到分子间 O-H 插入产物，而贫电子重氮化合物没有任何分解。添加 GaGl3 然后引发重氮丙二酸酯中的氮挤出，得到 1,5-C-H 插入产物。这种转化，其中由Rh(II)配合物催化的重氮化合物的分解可以从外部控制，代表了使用两种金属卡宾前体辅助串联催化的第一个例子。