The wide usage of N-heterocyclic carbenes (NHCs) has raised the quest for their deuterated molecules. Effective synthesis method to obtain them, however, has remained elusive. We present here a catalytic method for the preparation of deuterated NHCs, namely, the catalytic hydrogen–deuterium exchange reaction between NHCs and deuterated benzene using a coordinatively unsaturated Ru NHC catalyst. The catalytic system enables selective deuteration of the C(sp³)–H bonds of the alkyl groups on N-substituents, as well as the sterically nonhindered C(sp²)–H bonds of NHCs as demonstrated by the preparation of 16 deuterium-labeled NHCs that have a deuteration ratio on specified sites higher than 90%. The gram-scale synthesis of deuterated IMes indicated the applicability of this catalytic method. Mechanistic studies revealed that the high regio-selectivity toward those C(sp³)–H bonds on NHCs originates from the regio-selectivity of cyclometalation reactions of coordinatively unsaturated Ru NHC species.

中文翻译：

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配位不饱和钌 N-杂环卡宾催化剂合成氘标记 N-杂环卡宾的催化方法

N-杂环卡宾 (NHC)的广泛使用引发了对其氘化分子的探索。然而，获得它们的有效合成方法仍然难以捉摸。我们在这里提出了一种制备氘化 NHC 的催化方法，即使用配位不饱和 Ru NHC 催化剂在 NHC 和氘化苯之间进行催化氢-氘交换反应。该催化系统能够选择性地氘化N 取代基上烷基的 C(sp ³ )–H 键，以及空间位阻的 C(sp ²)–NHCs 的 H 键，如制备 16 个氘标记 NHCs 所证明的，这些 NHCs 在指定位点上的氘化率高于 90%。氘代 IMes 的克级合成表明该催化方法的适用性。机理研究表明，对NHC 上那些 C(sp ³ )-H 键的高区域选择性源于配位不饱和 Ru NHC 物种的环金属化反应的区域选择性。