Uranyl-silicotungstate-containing hybrid building units {α-SiW9} and {γ-SiW10} with excellent catalytic activities in the three-component synthesis of dihydropyrimidin-2(1H)-ones

Abstract

A novel uranyl-containing polytungstate, {K_4.2Na_18.9H_0.9(H₂O)₂₀[K₄(UO₂)₃(H₂O)₆(α-SiW₉O₃₄)(γ-SiW₁₀O₃₆)₃]}·ca.16H₂O (U₃), was synthesized using the Keggin-type precursor [γ-SiW₁₀O₃₆]⁸⁻ ({γ-SiW₁₀}) and UO₂(OAc)₂ and was further characterized by single-crystal X-ray diffraction and various techniques. Single crystal X-ray diffraction analysis showed a quadrahedron-like structure of U₃ with interesting tarot-like (top view) and crown-like (side view) views, among which one central {K₄(UO₂)₃(H₂O)₃} cluster was surrounded by one {α-SiW₉} and three {γ-SiW₁₀} building units. In addition, a more significant aspect is that U₃ shows good catalytic activity in the dehydration condensation of aldehydes, acetoacetates, and urea to green synthesize dihydropyrimidin-2(1H)-ones. The advantages of this transformation include solvent-free conditions, water as the sole by-product, available starting materials, good compatibility, and operational simplicity.