We report an unexpected rearrangement of a deprotonated picolyl-functionalized N-heterocyclic carbene (NHC) ligand from N,C-chelate to N,N-chelate in three-legged piano-stool Fe(II) and Ru(II) complexes. The reaction mechanism has been explored for one of the Fe(II) complexes. Experimental and computational studies suggest an unusual intermediate featuring a four-membered chelate ring, where the NHC and the α-carbon of one of the N-substituents coordinate to the Fe(II) center. A possible Fe-alkylidene intermediate has also been predicted by computations.

中文翻译：

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N-供体官能化的 N-杂环卡宾配体在第 8 族金属上的异常重排

我们报告了去质子化甲基吡啶官能化 N-杂环卡宾 (NHC) 配体在三足钢琴凳 Fe(II) 和 Ru(II) 复合物中从 N,C-螯合物到 N,N-螯合物的意外重排。已经探索了其中一种 Fe(II) 配合物的反应机理。实验和计算研究表明，一种不寻常的中间体具有四元螯合环，其中 NHC 和其中一个 N 取代基的 α-碳与 Fe(II) 中心配位。还通过计算预测了可能的 Fe-亚烷基中间体。