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Ionic Liquid Stabilized Niobium Oxoclusters Catalyzing Oxidation of Sulfides with Exceptional Activity
Author(s) -
Zhou Qingqing,
Ye Man,
Ma Wenbao,
Li Difan,
Ding Bingjie,
Chen Manyu,
Yao Yefeng,
Gong Xueqing,
Hou Zhenshan
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201806178
Subject(s) - catalysis , ionic liquid , niobium , allylic rearrangement , chemistry , substrate (aquarium) , carboxylate , oxidation state , inorganic chemistry , propionate , nuclear chemistry , organic chemistry , oceanography , geology
We present here a new class of niobium oxoclusters that are stabilized effectively by carboxylate ionic liquids. These functionalized ILs are designated as [TBA][LA], [TBA][PA], and [TBA][HPA] in this work, in which TBA represents tetrabutylammonium and LA, PA, and HPA refer to lactate, propionate, 3‐hydroxypropionate anions, respectively. The as‐synthesized Nb oxoclusters have been characterized by use of elemental analysis, NMR, IR, XRD, TGA, HRTEM. It was found that [TBA][LA]‐stabilized Nb oxoclusters (Nb−OC@[TBA][LA]) are uniformly dispersed with an average particle size of 2–3 nm and afforded exceptionally high catalytic activity for the selective oxidation of various thioethers. The turnover number with Nb−OC@[TBA][LA] catalyst was over 56 000 at catalyst loading as low as 0.0033 mol % (1 ppm). Meantime, the catalyst also showed the high activity for the epoxidation of olefins and allylic alcohols by using only 0.065 mol % of catalyst (50 ppm). The characterization of 93 Nb NMR spectra revealed that the Nb oxoclusters underwent structural transformation in the presence of H 2 O 2 but regenerated to their initial state at the end of the reaction. In particular, the highly dispersed Nb oxoclusters can absorb a large amount of polar organic solvents and thus were swollen greatly, which exhibited “pseudo” liquid phase behavior, and enabled the substrate molecules to be highly accessible to the catalytic center of Nb oxocluster units.