Binary Pd–Polyoxometalates and Isolation of a Ternary Pd–V–Polyoxomolybdate Active Species for Selective Aerobic Oxidation of Alcohols |
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| Authors: | Xianqiang Huang Xiaomei Zhang Dan Zhang Song Yang Xiao Feng Jikun Li Zhengguo Lin Jie Cao Ran Pan Dr. Yingnan Chi Prof. Bo Wang Prof. Changwen Hu |
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| Affiliation: | 1. Key Laboratory of Cluster Science, Ministry of Education, School of Chemistry, Beijing Institute of Technology, Beijing 100081 (P. R. China), Fax: (+86)?10‐68912631;2. Shandong Provincial Key Laboratory of Chemical Energy Storage and Novel Cell Technology, School of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng, 252059 (P. R. China) |
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| Abstract: | Binary Pd–polyoxometalates [Pd(dpa)2]3[PW12O40]2 ? 12 DMSO ( 2 ), [Pd(dpa)2]3[PMo12O40]2 ? 12 DMSO ? 2 H2O ( 3 ), and [Pd(dpa)(DMSO)2]2[HPMo10V2O40] ? 4 DMSO ( 4 ) were synthesized by reaction of [Pd(dpa)(OAc)2] ? 2 H2O ( 1 ; dpa=2,2′‐dipyridylamine) with three Keggin‐type polyoxometalates and fully characterized by single‐crystal and powder XRD analyses, IR spectroscopy, and elemental analyses. The synthesis is facile and straightforward, and the complicated ligand‐modification procedure often used in the traditional charge‐transfer method can be omitted. In 2 – 4 , Pd complexes and polyoxometalate anions are coupled through electrostatic interaction. Compound 4 is more active than the other three compounds in the selective aerobic oxidation of alcohols at ambient pressure. Interestingly, during catalytic recycling of compound 4 , unprecedented ternary Pd–V–polyoxometalate [Pd(dpa)2{VO(DMSO)5}2][PMo12O40]2 ? 4 DMSO ( 5 ), which was captured and characterized by single‐crystal XRD, proved to be the true active species and showed high catalytic activity for the selective aerobic oxidation of aromatic alcohols (98.1–99.8 % conversion, 91.5–99.1 % selectivity). Moreover, on the basis of control experiments and EPR and UV/Vis spectra, a plausible reaction mechanism for the oxidation of alcohols catalyzed by 5 was proposed. |
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| Keywords: | homogeneous catalysis oxidation palladium polyoxometalates vanadium |
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