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Supported Au Nanoparticles with N-Heterocyclic Carbene Ligands as Active and Stable Heterogeneous Catalysts for Lactonization
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2018-03-05 , DOI: 10.1021/jacs.8b01017
Rong Ye , Aleksandr V. Zhukhovitskiy , Roman V. Kazantsev , Sirine C. Fakra , Brent B. Wickemeyer , F. Dean Toste , Gabor A. Somorjai

Attachment of N-heterocyclic carbenes (NHCs) on the surface of metal nanoparticle (NP) catalysts permits fine-tuning of catalytic activity and product selectivity. Yet, NHC-coated Au NPs have been seldom used in catalysis beyond hydrogenation chemistry. One challenge in this field has been to develop a platform that permits arbitrary ligand modification without having to compromise NP stability toward aggregation or leaching. Herein, we exploit the strategy of supported dendrimer-encapsulated metal clusters (DEMCs) to achieve aggregation-stable yet active heterogeneous Au NP catalysts with NHC ligands. Dendrimers function as aggregation-inhibitors during the NP synthesis, and NHCs, well-known for their strong attachment to the gold surface, provide a handle to modify the stereochemistry, stereoelectronics, and chemical functionality of the NP surface. Indeed, compared to "ligandless" Au NPs which are virtually inactive below 80 °C, the NHC-ligated Au NP catalysts enable a model lactonization reaction to proceed at 20 °C on the same time scale (hours). Based on Eyring analysis, proto-deauration is the turnover-limiting step accelerated by the NHC ligands. Furthermore, the use of chiral NHCs led to asymmetric induction (up to 16% enantiomeric excess) in the lactonization transformations, which demonstrates the potential of supported DEMCs with ancillary ligands in enantioselective catalysis.

中文翻译:

具有 N-杂环卡宾配体的负载金纳米颗粒作为内酯化的活性和稳定的多相催化剂

N-杂环卡宾 (NHC) 在金属纳米颗粒 (NP) 催化剂表面的附着允许微调催化活性和产物选择性。然而,除了氢化化学之外,NHC 涂层的 Au NP 很少用于催化。该领域的一个挑战是开发一种平台,该平台允许任意配体修饰,而不必损害 NP 对聚集或浸出的稳定性。在此,我们利用负载树枝状聚合物包封的金属簇 (DEMC) 的策略来实现具有 NHC 配体的聚集稳定且活性的非均相 Au NP 催化剂。树枝状大分子在 NP 合成过程中起聚集抑制剂的作用,而众所周知的 NHCs 以其与金表面的强附着力而闻名,提供了改变立体化学、立体电子学、和 NP 表面的化学功能。事实上,与在 80°C 以下几乎不活跃的“无配体”Au NP 相比,NHC 连接的 Au NP 催化剂能够在 20°C 下以相同的时间尺度(小时)进行模型内酯化反应。根据 Eyring 分析,原脱氢是 NHC 配体加速的转换限制步骤。此外,手性 NHC 的使用导致内酯化转化中的不对称诱导(高达 16% 的对映体过量),这证明了带有辅助配体的支持型 DEMC 在对映选择性催化中的潜力。原脱氢是 NHC 配体加速的转换限制步骤。此外,手性 NHC 的使用导致内酯化转化中的不对称诱导(高达 16% 的对映体过量),这证明了带有辅助配体的支持型 DEMC 在对映选择性催化中的潜力。原脱氢是 NHC 配体加速的转换限制步骤。此外,手性 NHC 的使用导致内酯化转化中的不对称诱导(高达 16% 的对映体过量),这证明了带有辅助配体的支持型 DEMC 在对映选择性催化中的潜力。
更新日期:2018-03-05
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