- Effect of Linker Distribution in the Photocatalytic Activity of Multivariate Mesoporous Crystals
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The use of Metal-Organic Frameworks as crystalline matrices for the synthesis of multiple component or multivariate solids by the combination of different linkers into a single material has emerged as a versatile route to tailor the properties of single-component phases or even access new functions. This approach is particularly relevant for Zr6-MOFs due to the synthetic flexibility of this inorganic node. However, the majority of materials are isolated as polycrystalline solids, which are not ideal to decipher the spatial arrangement of parent and exchanged linkers for the formation of homogeneous structures or heterogeneous domains across the solid. Here we use high-throughput methodologies to optimize the synthesis of single crystals of UiO-68 and UiO-68-TZDC, a photoactive analogue based on a tetrazine dicarboxylic derivative. The analysis of the single linker phases reveals the necessity of combining both linkers to produce multivariate frameworks that combine efficient light sensitization, chemical stability, and porosity, all relevant to photocatalysis. We use solvent-assisted linker exchange reactions to produce a family of UiO-68-TZDC% binary frameworks, which respect the integrity and morphology of the original crystals. Our results suggest that the concentration of TZDC in solution and the reaction time control the distribution of this linker in the sibling crystals for a uniform mixture or the formation of core-shell domains. We also demonstrate how the possibility of generating an asymmetric distribution of both linkers has a negligible effect on the electronic structure and optical band gap of the solids but controls their performance for drastic changes in the photocatalytic activity toward proton or methyl viologen reduction.
- Lerma-Berlanga, Belén,R. Ganivet, Carolina,Almora-Barrios, Neyvis,Tatay, Sergio,Peng, Yong,Albero, Josep,Fabelo, Oscar,González-Platas, Javier,García, Hermenegildo,M. Padial, Natalia,Martí-Gastaldo, Carlos
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- Catalytic synthesis of Bi- and teraryls in aqueous medium with palladium(II) complexes of 2-(pyridine-2-ylmethylsulfanyl)benzoic acid
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Suzuki-Miyaura coupling reactions of phenylboronic and 1,4-phenylenediboronic acid with ArBr to form bi- and teraryls have been efficiently catalyzed by the air- and moisture-insensitive complexes [PdCl2L1] [1, L1 = 2-(pyridine-2-ylmethyl)sulfanylbenzoic acid; 0.05-0.5 mol-%] and [Pd(L2-H)2] (2, L2-H = 2-pyridin-2-yl-benzo[b]thiophen-3-ol; 0.01-0.5 mol-%). The complexes were formed by the reaction of [Pd(CH3CN)2Cl2] with L1, and the catalysis proceeds in water for 1. The loading of 0.1-0.5 mol-% of Pd is very promising for the coupling reactions to form teraryls. The COOH group imparts solubility to 1 in water. Ligand L2 is formed by the unprecedented cyclization of L1 in the course of the complexation reaction. The yield of 2 increases with the reaction time (5 h: 70%; 24 h: 85%). The two complexes and L1 have been characterized by NMR spectroscopy (1H and 13C{1H}). The single-crystal structures of 1 and 2 have been solved, and the Pd-S, Pd-N, and Pd-O bond lengths are 2.269(2), 1.999(6)-2.057(2), and 1.9787(17) A?, respectively. Nanoparticles (NPs) with a narrow size distribution (ca. 3.0-5.5 nm for 80-85% of the particles) formed at the start of these reactions and appear to be important for the catalytic coupling. Poisoning experiments and a two-phase test have shown that the catalysis is largely homogeneous and involves [Pd0-PdII] processes. The bond lengths and angles calculated by DFT are consistent with the experimental ones.
- Prakash, Om,Joshi, Hemant,Sharma, Kamal Nayan,Sharma, Alpesh Kumar,Singh, Ajai K.
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- STABILIZATION OF ACTIVE METAL CATALYSTS AT METAL-ORGANIC FRAMEWORK NODES FOR HIGHLY EFFICIENT ORGANIC TRANSFORMATIONS
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Metal-organic framework (MOFs) compositions based on post?synthetic metalation of secondary building unit (SBU) terminal or bridging OH or OH2 groups with metal precursors or other post-synthetic manipulations are described. The MOFs provide a versatile family of recyclable and reusable single-site solid catalysts for catalyzing a variety of asymmetric organic transformations, including the regioselective boryiation and siiylation of benzyiic C—H bonds, the hydrogenation of aikenes, imines, carbonyls, nitroarenes, and heterocycles, hydroboration, hydrophosphination, and cyclization reactions. The solid catalysts can also be integrated into a flow reactor or a supercritical fluid reactor.
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Paragraph 0222; 0224
(2019/01/07)
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