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A Tetranuclear Thorium-Containing Hexameric Antimonotungstate: Synthesis, Structure, and Catalysis of the Knoevenagel
Minghui Xiong1, Xiaoyue Wang1, Shudi Ji1
1Henan Key Laboratory of Polyoxometalate Chemistry, College of Chemistry and Molecular Sciences, Henan University, Kaifeng, Henan 475004, P. R. China.
Abstract:
A novel hexameric thorium-antimony-tungstate compound, [NH2(CH3)2]16Na10-{[(SbW9O32)(OH)(SbW9O31)(OH)2(SbW9O33)(Th2WSb9O13)(OH)4(H2O)]2}·57H2O (Th4Sb24), has been synthesized. It represents the first tetranuclear thorium-containing polyoxometalates (POMs) cluster, consisting of a [{(Th2WSb9O29)(OH)5(H2O)}2]22- ({Th4Sb18W2}) heterometallic cluster and six {SbW9} units, and it exhibits the highest Th and Sb nuclearity in POM chemistry. Th4Sb24 serves as an efficient heterogeneous catalyst for the Knoevenagel condensation under mild conditions, achieving 93% yield, a turnover number (TON) of 1860, and a turnover frequency (TOF) of 3720 h-1, while showing good recyclability and scalability. Mechanistic studies indicate a synergistic effect where the Lewis-acidic Th centers activate benzaldehyde, while the {SbW9} units facilitate proton abstraction. This work offers a viable strategy for designing high-nuclearity actinide POMs with practical catalytic utility.
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