Synthesis and characterization of a new copper-based polyoxomolybdate and its catalytic activity for azide-alkyne...

A new organic-functionalized Cu-based Anderson-type polyoxomolybdate, namely (C₇H₁₅N₄)₂[Na(H₂O)₄]₂[C₆H₁₂CuMo₆N₂O₂₄]·2(H₂O) (Cu^II-POM), was synthesized via a simple one-pot reaction and subsequently characterized using a range of analytical and spectral techniques. Structural investigation by single crystal X-ray diffraction analysis revealed that the polyanion component of the synthesized compound (i.e. [C₆H₁₂CuMo₆N₂O₂₄]^4-) possesses a δ-isomer Anderson-type structure, which is surrounded by four lattice water molecules and four [C₇H₁₅N₄-NaH₁₅(H₂O)₈]⁴⁺ cations in the crystal packing arrangement. The resulting double-sided tris-functionalized Anderson-type compound can function as highly effective heterogeneous photocatalysts for the copper(I)-catalyzed Huisgen azide-alkyne cycloaddition (Cu-AAC) reaction of terminal alkyne, benzyl halides, and sodium azide (acts as the azidonation and reducing agent) in aqueous media. Ultraviolet light irradiation enhances the catalytic activity of Cu^II-POM ~ 4.4 times of the "off" situation under reaction conditions of 0.00239 mmol cat., 80 °C, 8 h, 2 mL H₂O, So that the isolated yields for the AAC reaction involving a variety of terminal alkynes and benzyl halides using the Cu^II-POM catalyst ranged between 19-97%. The current study is the first report about using an efficient and economical Cu(II)-POM/UV/NaN₃ catalytic system in the Cu-AAC reaction and reveals its significant potential for applying to other Cu(I)-catalyzed reactions.