Organisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.uni-heidelberg.de/fakultaeten/chemgeo/oci/akstraub.
Angew Chem Int Ed Engl. 2015 Jun 15;54(25):7431-5. doi: 10.1002/anie.201502368. Epub 2015 Apr 29.
A molecularly defined copper acetylide cluster with ancillary N-heterocyclic carbene (NHC) ligands was prepared under acidic reaction conditions. This cluster is the first molecular copper acetylide complex that features high activity in copper-catalyzed azide-alkyne cycloadditions (CuAAC) with added acetic acid even at -5 °C. Ethyl propiolate protonates the acetate ligands of the dinuclear precursor complex to release acetic acid and replaces one out of four ancillary ligands. Two copper(I) ions are thereby liberated to form the core of a yellow dicationic C2-symmetric hexa-NHC octacopper hexaacetylide cluster. Coalescence phenomena in low-temperature NMR experiments reveal fluxionality that leads to the facile interconversion of all of the NHC and acetylide positions. Kinetic investigations provide insight into the influence of copper acetylide coordination modes and the acetic acid on catalytic activity. The interdependence of "click" activity and copper acetylide aggregation beyond dinuclear intermediates adds a new dimension of complexity to our mechanistic understanding of the CuAAC reaction.
在酸性反应条件下制备了具有辅助 N-杂环卡宾 (NHC) 配体的分子定义的铜乙炔化物簇。该簇是第一个分子铜乙炔化物配合物，即使在 -5°C 下，在添加乙酸的铜催化叠氮化物-炔烃环加成 (CuAAC) 中也具有高活性。乙基丙炔酸将二核前体配合物的乙酸盐配体质子化，释放出乙酸并取代四个辅助配体中的一个。两个铜 (I) 离子因此被释放出来，形成黄色二阳离子 C2 对称六 NHC 八铜六乙炔化物簇的核心。低温 NMR 实验中的聚结现象揭示了流动性，导致所有 NHC 和乙炔化物位置的易于相互转化。动力学研究提供了对铜乙炔化物配位模式和乙酸对催化活性影响的深入了解。“点击”活性和铜乙炔化物聚合超越双核中间体的相互依存关系为我们对 CuAAC 反应的机械理解增添了新的复杂性。
