N-Heterocyclic carbenes: deducing σ- and π-contributions in Rh-catalyzed hydroboration and Pd-catalyzed coupling reactions

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• 作者：Dimitri M. Khramov ; Evelyn L. Rosen ; Joyce A.V. Er ; Peter D. Vu ; Vincent M. Lynch ; Christopher W. Bielawski
• 关键词：Helicenes ; Heck reaction ; Enantiomeric resolution ; Photodehydrocyclisation ; Azahelicenes
• 刊名：Tetrahedron
• 出版年：2008
• 出版时间：14 July 2008
• 年：2008
• 卷：64
• 期：29
• 页码：6853-6862
• 全文大小：506 K

文摘

The effect of tuning the electronic properties of N-heterocyclic carbene (NHC) ligands was evaluated in multiple, mechanistically distinct, metal-mediated reactions. Hydroboration and Heck reactions, catalyzed by Rh–NHC and Pd–NHC complexes, respectively, were found to result in yields that were up to ten times lower when π-withdrawing substituents were incorporated into the NHC backbone relative to analogues bearing σ-withdrawing groups.