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

Abstract

Polyoxometalates (POMs) are widely applied as tuneable and versatile catalysts for a variety of oxidation reactions in an aqueous/organic twophase 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 (KCl 4 )Na 7 [(β-CD) 3 (SiW 12 O 40 )]•9H 2 O {3CD@SiW 12 } for various oxidation catalyses. In contrast to free CD, Keggin [SiW 12 O 40 ] 4− catalysts, and their mixture, the {3CD@SiW 12 } 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.

Redox-Responsive Host–Guest Association between γ-Cyclodextrin and Mixed-Metal Keggin-Type Polyoxometalates

“…The chaotropic character of Keggin POMs has been clearly demonstrated, while some of them have even been identified as superchaotrope entities according to the Hofmeister classification. ,, Indeed, it has recently been shown that the strength of such supramolecular host–guest associations depends mainly on the charge density of the POM. , Furthermore, ITC measurements revealed that processes driven by the chaotropic effect exhibit specific thermodynamic signatures corresponding to enthalpy gain correlated to entropic penalty . Some of these hybrid CD/Keggin composites have shown improved performances in catalysis or adsorption, for which cooperative effects should play a crucial role. Therefore, a deeper characterization of the interactions between γ-CD and mixed-metal Keggin POMs is needed for a better understanding of the synergetic effect between the two components and further innovative development of advanced composite materials.…”

“…10,11 Furthermore, ITC measurements revealed that processes driven by the chaotropic effect exhibit specific thermodynamic signatures corresponding to enthalpy gain correlated to entropic penalty. 11 Some of these hybrid CD/ Keggin composites have shown improved performances in catalysis 18 or adsorption, 19 for which cooperative effects should play a crucial role. Therefore, a deeper characterization of the interactions between γ-CD and mixed-metal Keggin POMs is needed for a better understanding of the synergetic effect between the two components and further innovative development of advanced composite materials.…”

Host‐Guest Complexation Between Cyclodextrins and Hybrid Hexavanadates: What are the Driving Forces?

“…[2] Among the commercially available organic building units, cyclodextrins (CDs) as natural amphiphilic macrocyclic polysaccharides are particularly useful to develop host-guest systems with POMs, offering the possibility to design self-healing, stimuli-responsive, catalytic or energy-related systems. [3][4][5][6][7][8][9] The inclusion complexes involving CDs and POMs can be roughly divided in two families. In one hand, hybrid POMs with grafted organic ligands can exhibit high affinity towards hydrophobic hosting cavity.…”

Supramolecular assemblies of organo-functionalised hybrid polyoxometalates: from functional building blocks to hierarchical nanomaterials

“…This is largely thanks to the complementarity of their molecular structures and is driven predominantly by favourable steric-fitting between the host and the guest oxocluster, and some hydrogen-bonding interactions. 21,86,184 Such inclusion complexes are stable in both solution and the solid-state and have recently been studied for their phase-transfer catalytic properties, 185 and as a novel tool for probing the self-assembly behaviours of small POMs by mass spectrometry. 186,187 That said, the formation of stable host-guest complexes between conventional POMs and cavitands (particularly curcubiturils and pillar-arenes, which do not share the excellent complementarity found in POMCCD systems) remains the exception rather than the rule, and in many cases, POM@cavitand complexes form crystalline networks in which the POM remains external to the macrocyclic cavity and often requires additional functionalisation of the macrocycle (e.g.…”