Zr-Metal–Organic Frameworks Featuring TEMPO Radicals: Synergistic Effect between TEMPO and Hydrophilic Zr-Node Defects Boosting Aerobic Oxidation of Alcohols

Abstract

Metal–organic frameworks (MOFs) featuring multiple catalytic units are excellent platforms for heterogeneous catalysis. However, the synergism between multiple catalytic units for catalysis is far from being well understood. Herein, we reported the synthesis of a robust 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) radical-functionalized Zr-MOF (UiO-68-TEMPO) in the form of single-crystalline and microsized crystals with varied missing linker defects. Detailed catalytic studies and theoretical calculations reveal that the synergistic effect between the TEMPO radicals and hydrophilic and defective Zr-nodes endows UiO-68-TEMPO with superior catalytic activity toward aerobic oxidation of alcohols. Our work not only offers a new route to design and synthesize highly effective MOF catalysts but also provides insights into the synergism between multiple catalytic sites.

Electroactive Organic Building Blocks for the Chemical Design of Functional Porous Frameworks (MOFs and COFs) in Electronics

“…[157] NA [157], [ [226] MOFs: Catalysis for aerobic oxidation reactions 1310 Ref. [229] NA [227]- [229] COFs: Energy storage, dynamic nuclear polarization (DNP) last decades ome examples of conductive MOFs exhibiting high chargem obility have emerged based on "through-bond" and "through-space" design approaches. [19,29,44,45] The "through-bond" approach is based on the promotion of charge transport in MOFs through covalent bondingt hanks to an effective overlapo ft he metal and ligand orbitals, exemplified by TCNQ@HKUST-1 [46] and severalt wo-dimensional MOFs built from, for example, planar triphenylene-based ligands in which functional groups play an important role for attaining high electrical conductivity.…”

“…More recently,T EMPO-decorated UiO-66, UiO-67 and UiO-68 MOFs have been synthesized under mild conditions and have been shown to be efficient catalysts fort he selective aerobic oxidation of alcohols. [228,229] In these studies, the authors prepared the TEMPO-substituted MOFs using an ew HClmodulated and low-temperature method to avoid the decompositiono ft he radicals, obtaining highly defective materials with surfacea reas( up to 1310m 2 g À1 )h igher than the parent frameworks. The radical-based catalysts are highly activea nd recyclable for the aerobic oxidation of alcohols under ambient conditions.…”

Strategies in Metal–Organic Framework‐based Catalysts for the Aerobic Oxidation of Alcohols and Recent Progress

“…In 2019, Zhuang and co‐workers studied the synergic effect between TEMPO on MOFs and metal node defects for aerobic oxidation 29 . A terphenyl system was employed for UiO‐68 preparation, and TEMPO‐functionalized UiO‐68‐TEMPO was obtained using an acid modulator.…”

“…In 2019, Zhuang and co-workers studied the synergic effect between TEMPO on MOFs and metal node defects for aerobic oxidation. 29 A terphenyl system was employed for UiO-68 preparation, and TEMPO-functionalized UiO-68-TEMPO was obtained using an acid modulator. Monocarboxylic acids, such as benzoic acid, have been generally been used as modulators for crystal growth, and competing reactions between monocarboxylates and dicarboxylates for MOF formation could generate structural defects in the MOF crystals.…”

Post‐Synthetic Modification of Metal‐Organic Frameworks Bearing Phenazine Radical Cations for aza‐Diels‐Alder Reactions

“…[9] MOFs consisting of organic radicals usually exhibit intriguing optical, electronic, magnetic, and chemo-catalytic properties, and thus have demonstrated great potential applications in optical, electronic, and magnetic devices, and as catalysts. [10][11][12][13][14][15] However, the preparation of MOFs bearing stable organic radicals is very challenging because most organic radicals are highly reactive and difficult to incorporate into the framework of MOFs. Generally, the well-developed pre-or post-synthetic modification approaches have been widely applied to introduce organic radical centers into the framework of MOFs (Figure 1).…”