Tris functionalized Cu-centered cyclohexamolybdate molecular armor as a bimetallic catalyst for rapid p-nitrophenol hydrogenation

Abstract

A water-soluble tris functionalized Cu-centered Anderson nanocluster (NH₄)₄{[NH₂C(CH₂O)₃]₂CuMo₆O₁₈} with a remote NH₂ motif was synthesized for the first time. The bimetallic cluster's structure is identified by single crystal X-ray diffraction, and it is also further well characterized by a combination of technologies, such as XPS, TGA, FT-IR spectroscopy, UV-Vis spectroscopy, ESI-MS, and EA spectroscopy. It can serve as a non-noble metal containing bimetallic catalyst to afford rapid reduction of aqueous p-nitrophenol to p-aminophenol (10 min) with a promising conversion (a decent 100%) and perfect selectivity (ca. 99%) in aqueous solution at room temperature. The catalytic reaction rate constant of the bimetallic {[NH₂C(CH₂O)₃]₂CuMo₆O₁₈}⁴⁻ catalyst was one order higher (ca. 9.4 times) than that of the corresponding monometallic [Mo₇O₂₄]⁶⁻ catalyst. The bimetallic cluster shows good catalytic performance and recyclability with an intact structure, confirmed by powder XRD. Cyclic voltammetry investigation indicated that a reversible two one-electron process was observed, in which Cu^II/Cu^I and Mo^VI/Mo^V were the redox couples and served as an ideal electrochemically stable multi-electron reservoir to promote the reduction process that enabled an obvious bimetallic synergistic catalytic performance during such p-nitrophenol hydrogenation reduction.