Self-Assembly of a U(VI)-Containing Polytungstate Tetramer with Lewis Acid-Base Catalytic Activity for a Dehydration Condensation Reaction

Abstract

A novel U(VI)-containing polytungstate (U-POW) tetramer, {K1.37Na26.63[K2(UO2)4Cl0.5(OH)5.5(γ-SiW10O36)4]}·ca66H2O (U 4 ), was synthesized using the Keggin-type precursor [γ-SiW10O36]8– and UO2(NO3)2. U 4 was further characterized by single-crystal X-ray diffraction, FT-IR, Raman spectroscopy, solid-state diffuse reflection spectroscopy, ICP-OES, ESI-MS, TGA, and PXRD. The central {K2(UO2)4Cl0.5(OH)5.5} chromophore was constructed dexterously from four uranyl, four halves of K ions, 5.5 bridging μ2-OH, and disordered Cl ions, and was further stabilized by four {γ-SiW10} moieties to construct the tetramer [K2(UO2)4Cl0.5(OH)5.5(γ-SiW10O36)4]28–. Notably, U 4 could work as an effective bifunctional Lewis acid-base catalyst for the synthesis of pyrazoles via the condensation of hydrazines with 1,3-diketones under mild conditions, which is attributed to the synergetic effect of the Lewis acidity of U(VI) and the Lewis basicity of {γ-SiW10}.

Polyoxometalate catalysts for the synthesis of N-heterocycles

“…Later, they synthesized five U-POMs with different 2D/3D structures based on {Na 2 (UO 2 ) 2 (XW 9 O 34 ) 2 } (X = P, Si), in which a {Na 2 (UO 2 ) 2 } cluster is sandwiched between two {XW 9 } (Fig. 13(c)) [118][119][120]. These compounds showed how distinct reaction conditions could lead to the different assembly conditions for Na-H under solvent-free conditions (Fig.…”

Recent Advances in the Synthesis of Pyrazole Derivatives: A Review

“…This innovative protocol benefits from the use of resinous, nontoxic, thermally stable, and cost-effective Amberlyst-70 as a heterogeneous catalyst, in addition to offering a simple reaction workup, thus presenting valuable eco-friendly attributes. Liu et al [21] made an exciting discovery of a novel Keggin-based U-POW (U(VI)containing polytungstates) tetramer, referred to as U4. This tetramer showcased remarkable bifunctional Lewis s acid-base catalytic properties and exhibited excellent performance in the synthesis of pyrazoles 38 via the condensation of diverse hydrazines 37 with 1,3-diketones 36 under mild reaction conditions (see Scheme 12).…”

Highly-stable Silverton-type UIV-containing polyoxomolybdate frameworks for the heterogeneous catalytic synthesis of quinazolinones

“…22,23 U-POMs have been studied since the early 1970s, 24 and dozens of Keggin-type U-POMs, several Dawson-type, and other type structures were reported. 21,25,26 Generally, UO 2 2+ and U 4+ ions in the reported structures act as links or insertion atoms sandwiched by POM moieties, while U 4+ ions can be used as heteroatoms only in Silverton-type U-POMs. From 1981 to 1990, Torchenkova and co-workers reported nine Silvertontype {UMo 12 }-based structures, most of which are 0D structures.…”