Cluster-Cluster Co-Nucleation Induced Defective Polyoxometalate-Based Metal-Organic Frameworks for Efficient Tandem Catalysis.

The construction of defective sites is one of the effective strategies to create high-activity Metal-Organic frameworks (MOFs) catalysts. However, traditional synthesis methods usually suffer from cumbersome synthesis steps and disordered defect structures. Herein, a cluster-cluster co-nucleation (CCCN) strategy is presented that involves the in situ introduction of size-matched functional polyoxometalates (H6P2W18O62, {P2W18}) to intervene the nucleation process of cluster-based MOFs (UiO-66), achieving one-step inducement of exposed defective sites without redundant post-processing. POM-induced UiO-66 ({P2W18}-0.1@UiO-66) exhibits a classical reo topology for well-defined cluster defects. Moreover, the defective sites and the interaction between POM and skeletal cluster nodes are directly observed by Integrated Differential Phase Contrast in Scanning Transmission Electron Microscopy (iDPC-STEM). Owing to the molecular-level proximity between defective sites and POM in the same nano-reaction space, {P2W18}-0.1@UiO-66 exhibits efficient tandem catalysis in the preparation of γ-valerolactone (γ-GVL) from laevulinic acid (LA) by the combination of Lewis and Brønsted acids with 11 times higher performance than defective UiO-66 formed by conventional coordination modulation strategy. The CCCN strategy is applicable to different POM and has the potential to be extended to other cluster-based MOFs, which will pave a new way for the construction of functional MOFs with multi-centered synergistic catalysis.

Coordination Defect-Induced Frustrated Lewis Pairs in Polyoxo-metalate-Based Metal-Organic Frameworks for Efficient Catalytic Hydrogenation.

Precise control of the structure and spatial distance of Lewis acid (LA) and Lewis base (LB) sites in a porous system to construct efficient solid frustrated Lewis pair (FLP) catalyst is vital for industrial application but remains challenging. Herein, we constructed FLP sites in a polyoxometalate (POM)-based metal-organic framework (MOF) by introducing coordination-defect metal nodes (LA) and surface-basic POM with abundant oxygen (LB). The well-defined and unique spatial conformation of the defective POM-based MOF ensure that the distance between LA and LB is at ~4.3 Å, a suitable distance to activate H2 . This FLP catalyst can heterolytically dissociate H2 into active Hδ- , thus exhibiting high activity in hydrogenation, which is 55 and 2.7 times as high as that of defect-free POM-based MOF and defective MOF without POM, respectively. This work provides a new avenue toward precise design multi-site catalyst to achieve specific activation of target substrate for synergistic catalysis.

Design of a Polyoxometalate-Based Metal-Organic Framework for Photocatalytic C(sp3)-H Oxidation of Toluene.

A powerful and promising route for developing novel photocatalysts for light-driven toluene oxidation in water under mild conditions is presented. Herein, a novel polyoxometalate-based metal-organic framework (POMOF), {Co4W22-DPNDI}, is prepared by incorporating the unusual Co4-sandwiched POM anion [Co4(µ-OH)2(SiW11O39)2]10- ({Co4W22}) and the photoactive organic bridging link N,N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI) into a framework. {Co4W22} is a good candidate for photocatalytic water oxidation. DPNDI is easily excited to form the radical species DPNDI* in the presence of an electron donor, which is beneficial for activation of the inert O2. Anion···π interactions and covalent bonds between {Co4W22} and DPNDI facilitate electron-hole separation and electron transfer. {Co4W22-DPNDI} displays high catalytic activity for the activation of the C(sp3)-H bond of toluene using light as a driving force and inexpensive water as an oxygen source under mild conditions. In particular, the yield and selectivity are improved by replacing oxygen with water, which may be ascribed to the release of protons during the water oxidation process that facilitate the generation of •OH.

A hydrophilic inorganic framework based on a sandwich polyoxometalate: unusual chemoselectivity for aldehydes/ketones with in situ generated hydroxylamine.

A hydrophilic inorganic porous catalyst was prepared via the hydrothermal method. The combination of [WZn3(H2O)2(ZnW9O34)2]12- and Co(ii) provides a synergistical catalytic way to promote oximation of aldehyde/ketone with in situ generated hydroxylamine that initially produces an oxime, which further either dehydrates into a nitrile or undergoes a Beckmann rearrangement to form an amide.