文献类型：期刊文献

英文题名：Identifying Catalytically Active Mononuclear Peroxoniobate Anion of Ionic Liquids in the Epoxidation of Olefins

作者：Ma, Wenbao[1];Yuan, Haiyang[1];Wang, Haifeng[1];Zhou, Qingqing[1];Kong, Kang[1];Li, Difan[1];Yao, Yefeng[2,3];Hou, Zhenshan[1]

机构：[1]East China Univ Sci & Technol, Res Inst Ind Catalysis, Key Lab Adv Mat, Shanghai 200237, Peoples R China;[2]East China Normal Univ, Phys Dept, Shanghai 200062, Peoples R China;[3]East China Normal Univ, Shanghai Key Lab Magnet Resonance, Shanghai 200062, Peoples R China

年份：2018

卷号：8

期号：5

起止页码：4645

外文期刊名：ACS CATALYSIS

收录：;EI(收录号：20181905141640);WOS:【SCI-EXPANDED(收录号:WOS:000431727300101)】；

基金：The authors are grateful for financial support from the National Natural Science Foundation of China (21373082, 21622305, 21773061), the Innovation Program of the Shanghai Municipal Education Commission (15ZZ031), and the Fundamental Research Funds for the Central Universities.

语种：英文

外文关键词：peroxoniobate; ionic liquid; epoxidation; olefins; DFT

摘要：The organic carboxylic acid coordinated monomeric peroxoniobate-based ionic liquids (ILs) [TBA][NbO(OH)(2)(R)] (TBA = tetrabutylammonium; R = lactic acid (LA), glycolic acid (GLY), malic acid (MA)) were prepared and fully characterized by elemental analysis, NMR, IR, Raman, TGA, Nb-93 NMR, and HRMS. These IL catalysts exhibited not only high catalytic activity for the epoxidation of olefins under very mild reaction conditions, as the turnover frequency of [TBA][NbO(OH)(2)(LA)] reached up to 110 h(-1), but also satisfactory recyclability in the epoxidation by using only 1 equiv of hydrogen peroxide as an oxidant. Meanwhile, this work revealed that the ILs underwent structural transformation from [NbO(OH)(2)(R)](-) to [Nb(O-O)(2)(R)]- (R = LA, GLY, MA) in the presence of H2O2 by a subsequent activity evaluation, characterization, and first-principles calculations. Moreover, the organic carboxylic acid coordinated monomeric peroxoniobate-based ILs were investigated using density functional theory (DFT) calculations, which identified that [Nb(O-O)(2)LA](-) was more advantageous than [Nb(O-O)(2)(OOH)(2)](-) for the epoxidation of olefins. Due to the coordination between the a-hydroxy acids and the monomeric peroxoniobate anions, the functionalized ILs can efficiently catalyze the epoxidation of a wide range of olefins and allylic alcohols under very mild conditions. Additionally, the effect of solvents on the reaction is illustrated. It was found that methanol can lower the epoxidation barriers by forming a hydrogen bond with a peroxo ligand attached to the niobium center.