Self-Assembled Supramolecular Polyoxometalate Hybrid Architecture as a Multifunctional Oxidation Catalyst

Polyoxometalates
(POMs) are widely applied as tuneable and versatile
catalysts for a variety of oxidation reactions in an aqueous/organic
two-phase system. However, the practical applications of POMs-based
biphasic catalysis are hampered by low space-time yields and mass-transport
limitation between two layers due to extremely low solubility of the
organic reactants in the aqueous phase. Here, we first introduced
β-cyclodextrin (β-CD) as an inverse phase transfer agent
and a supramolecular nanoreactor to construct a supramolecular POM
inorganic–organic hybrid framework (KCl4)­Na7[(β-CD)3(SiW12O40)]·9H2O {3CD@SiW12} for various
oxidation catalyses. In contrast to free CD, Keggin [SiW12O40]4– catalysts, and their mixture,
the {3CD@SiW12} catalyst, efficiently
catalyze oxidation reactions of alcohol, alkene, and thiophene. A
comprehensive strategy of experimental, crystallographic, and density
functional theory (DFT) calculations elucidates that the catalytic
pathway involved three combined aspects of supramolecular recognition,
phase transfer property, and POM catalysis. The strategic combination
of supramolecular characteristic and POM-based catalysts to fabricate
supramolecular POM hybrid materials opens up new economic and green
tuning options, thus paving the way to informed catalyst design.

多金属氧酸盐（Polyoxometalates，POMs）作为可精准调控、用途广泛的催化剂，被广泛应用于水/有机两相体系中的各类氧化反应。然而，基于POMs的两相催化体系的实际应用却受限于较低的时空产率，以及因有机反应物在水相中溶解度极低而引发的两相界面传质限制。本研究首次引入β-环糊精（β-cyclodextrin，β-CD）作为反相转移剂与超分子纳米反应器，构建了超分子POM无机-有机杂化框架材料KCl₄·Na₇[(β-CD)₃(SiW₁₂O₄₀)]·9H₂O（命名为{3CD@SiW₁₂}），用于各类氧化催化反应。相较于游离的β-CD、凯金型（Keggin）[SiW₁₂O₄₀]⁴⁻催化剂以及二者的混合物，{3CD@SiW₁₂}催化剂可高效催化醇、烯烃与噻吩的氧化反应。本研究通过实验表征、晶体学分析与密度泛函理论（density functional theory，DFT）计算相结合的综合研究策略，阐明了该催化路径涵盖超分子识别、相转移性能与POM催化三大协同作用机制。将超分子特性与POM基催化剂进行策略性结合以制备超分子POM杂化材料，为开发经济绿色的催化调控新路径提供了可能，也为智能催化剂的定向设计铺平了道路。