EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, UK.
Nat Protoc. 2011 Jan;6(1):69-77. doi: 10.1038/nprot.2010.177. Epub 2010 Dec 16.
We describe the synthesis of commonly used free N-heterocyclic carbenes (NHCs), 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr), and of the two corresponding ruthenium-based metathesis complexes. The complex containing IMes was found to be highly efficient in macrocyclizations involving ring-closing metatheses (RCM), whereas the complex featuring the IPr ligand shows excellent activity in both RCM and cross metathesis because of its greater stability. The free carbenes IMes and IPr are isolated in four steps, with an overall yield of ∼50%. They are then used to replace a labile phosphine in precatalysts belonging to two families of ruthenium-containing complexes, benzylidene and indenylidene types, respectively. Such complexes are isolated as analytically pure compounds with 77% and 95% yield. The total time for the synthesis of the free NHCs is 56 h, and incorporation in complexes requires an additional 4-5 h.
我们描述了常用的游离 N-杂环卡宾（NHC）的合成，1,3-双-(2,4,6-三甲基苯基)咪唑-2-亚基（IMes）和 1,3-双-(2,6-二异丙基苯基)咪唑-2-亚基（IPr），以及两种相应的钌基复分解配合物。含有 IMes 的配合物在涉及闭环复分解（RCM）的大环化反应中表现出很高的效率，而含有 IPr 配体的配合物由于其更高的稳定性，在 RCM 和交叉复分解中都表现出优异的活性。游离卡宾 IMes 和 IPr 经过四步分离，总收率约为 50%。然后，它们被用来取代分别属于两种类型的钌配合物，苄叉型和茚基型的前催化剂中不稳定的膦。这些配合物以分析纯化合物的形式分离出来，产率分别为 77%和 95%。游离 NHC 的总合成时间为 56 小时，而在配合物中的引入则需要额外的 4-5 小时。
