An iron-containing POM-based hybrid compound as a heterogeneous catalyst for one-step hydroxylation of benzene to phenol

Abstract

It is a major challenge to perform one-pot hydroxylation of benzene to phenol under mild conditions, which replaces the environmentally harmful cumene method. Thus, finding highly efficient heterogeneous catalysts that can be recycled is extremely significant. Herein, a (POM)-based hybrid compound {[Fe^II(pyim)₂(C₂H₅O)][Fe^II(pyim)₂(H₂O)][PMo^V₂Mo^VI₉V^IV₃O₄₂]}·H₂O (pyim = 2-(2-pyridyl)benzimidazole) (Fe₂-PMo₁₁V₃) was successfully prepared by hydrothermal synthesis using typical Keggin POMs, iron ions and pyim ligands. Single-crystal diffraction shows that the Fe-pyim unit in Fe₂-PMo₁₁V₃ forms a stable double-supported skeleton by Fe–O bonding to the polyacid anion. Remarkably, due to the introduction of vanadium, Fe₂-PMo₁₁V₃ forms a divanadium-capped conformation. Benzene oxidation experiments indicated that Fe₂-PMo₁₁V₃ can catalyze the benzene hydroxylation reaction to phenol in a mixed solution of acetonitrile and acetic acid containing H₂O₂ at 60 °C, affording a phenol yield of about 16.2% and a selectivity of about 94%.