Transfer Hydrogenation from Glycerol: Activity and Recyclability of Iridium and Ruthenium Sulfonate-Functionalized N-Heterocyclic Carbene Catalysts
Transfer Hydrogenation from Glycerol: Activity and Recyclability of Iridium and Ruthenium Sulfonate-Functionalized N-Heterocyclic Carbene Catalysts
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DOI：
10.1021/acssuschemeng.6b03156
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发表时间：
2017-05-01
影响因子：
8.4
通讯作者：
Voutchkova-Kostal, Adelina
中科院分区：
文献类型：
--
作者：
Azua, Arturo;Finn, Matthew;Voutchkova-Kostal, Adelina
以纯甘油为氢供体和溶剂，比较了三种钌（II）和两种铱（III） n -杂环羰基（NHC）配合物在亚胺、醛、酮和烯烃的转移加氢反应中的活性和选择性。五种催化剂中的四种可能通过一氢化机制进行，并且对亚胺的转移氢化反应比醛、酮和烯烃更活跃。第五种催化剂可能是通过二氢化机制进行的，并且对羰基比亚胺和烯烃更有活性。乳酸是甘油唯一可检测的副产物。1,10-菲罗啉的定量中毒实验表明，主要的催化活性物质是一种与毒素结合较弱的结扎均匀络合物。探讨了催化剂回收利用的潜力：与铱催化剂和钌单NHC催化剂相比，具有螯合配体的NHC钌催化剂具有更强的鲁棒性和可回收性。其原因可以追溯到催化剂在有甘油和KOH存在而没有底物的情况下降解的相对速度。只有当甘油与异丙醇允许钌催化剂完全可回收时，才会观察到这种降解。
Three ruthenium(II) and two iridium(III) N-heterocyclic carbene (NHC) complexes functionalized with sulfonates are compared with respect to their activity and selectivity for the transfer hydrogenation of imines, aldehydes, ketones, and olefins using neat glycerol as hydrogen donor and solvent. Four of the five catalysts likely proceed through a monohydride mechanism and are more active for transfer hydrogenation of imines than aldehydes, ketones, and olefins. The fifth catalyst likely proceeds through a dihydride mechanism and is found to be more active for carbonyls than imines and olefins. Lactic acid is observed as the only detectable byproduct from glycerol. Quantitative poisoning experiments with 1,10-phenanthroline suggest that the predominant catalytically active species is a ligated homogeneous complex with weak binding to the poison. The potential for catalyst recycling is explored: the ruthenium NHC catalysts with chelating ligands are found to be more robust and recyclable relative to the iridium catalysts and the ruthenium mono-NHC catalyst. The reason is traced to the relative rate of degradation of the catalyst in the presence of glycerol and KOH but no substrate. This degradation is only observed when glycerol with isopropanol allows the ruthenium catalyst to be fully recyclable.