Binary Pd-polyoxometalates and isolation of a ternary Pd-V-polyoxomolybdate active species for selective aerobic oxidation of alcohols.
Binary Pd-polyoxometalates [Pd(dpa)2]3 [PW12 O40]2 ⋅12 DMSO (2), [Pd(dpa)2]3 [PMo12 O40]2 ⋅12 DMSO⋅2 H2 O (3), and [Pd(dpa)(DMSO)2]2 [HPMo10 V2 O40 ]⋅4 DMSO (4) were synthesized by reaction of [Pd(dpa)(OAc)2]⋅2 H2 O (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][PMo12 O40]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.
Key Laboratory of Cluster Science, Ministry of Education, School of Chemistry, Beijing Institute of Technology, Beijing 100081 (P. R. China), Fax: (+86) 10-68912631; 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).
Xianqiang
X
Huang
Xiaomei
X
Zhang
Dan
D
Zhang
Song
S
Yang
Xiao
X
Feng
Jikun
J
Li
Zhengguo
Z
Lin
Jie
J
Cao
Ran
R
Pan
Yingnan
Y
Chi
Bo
B
Wang
Changwen
C
Hu
homogeneous catalysis; oxidation; palladium; polyoxometalates; vanadium