Visible-Light-Induced Phenoxyl Radical-based Metal-Organic Framework for Selective Photooxidation of Sulfides

Dual-linker Ir-Zr-MOF shows improved porosity to enhance aqueous sulfide photooxidation

The hetero photooxidation of sulfide under aqueous conditions is of great importance in the green synthesis of sulfoxide. This process requires a type of solid photocatalyst with the properties of high porosity and water stability, as well as photosensitivity. Herein, a stable Ir-Zr-MOF material (compound 1) with high porosity is assembled from two linear linkers of a 2-phenylquinoline-4-carboxylic acid-Ir(III) complex (Irphen) and 4,4'-stilbenedicarboxylic acid (H2SDC), and a Zr6 cluster. 1 is isostructural to JLU-Liu34 with a composition of [Zr6O4.78(OH)3.22(SDC)3.82(Irphen)0.78TFA2.8]·2.8MeOH and permanent porosity with a BET surface area of 1507 m2 g-1. 1 exhibits improved activity for the photocatalytic aerobic oxidation of sulfide to sulfoxide via blue light irradiation under aqueous conditions. Mechanism studies demonstrate that a superoxide radical is the reactive oxygen species in the sulfide photooxidation. 1 can be readily recycled and reused at least 5 times without loss of catalytic activity. This work not only provides a good strategy for the assembly of an Ir(III) complex into MOFs but also an efficient method for the green synthesis of sulfoxide.

Metal-organic frameworks for organic transformations by photocatalysis and photothermal catalysis

Organic transformation by light-driven catalysis, especially, photocatalysis and photothermal catalysis, denoted as photo(thermal) catalysis, is an efficient, green, and economical route to produce value-added compounds. In recent years, owing to their diverse structure types, tunable pore sizes, and abundant active sites, metal-organic framework (MOF)-based photo(thermal) catalysis has attracted broad interest in organic transformations. In this review, we provide a comprehensive and systematic overview of MOF-based photo(thermal) catalysis for organic transformations. First, the general mechanisms, unique advantages, and strategies to improve the performance of MOFs in photo(thermal) catalysis are discussed. Then, outstanding examples of organic transformations over MOF-based photo(thermal) catalysis are introduced according to the reaction type. In addition, several representative advanced characterization techniques used for revealing the charge reaction kinetics and reaction intermediates of MOF-based organic transformations by photo(thermal) catalysis are presented. Finally, the prospects and challenges in this field are proposed. This review aims to inspire the rational design and development of MOF-based materials with improved performance in organic transformations by photocatalysis and photothermal catalysis.

A Green Environmental Protection Photocatalytic Molecular Reactor for Aerobic Oxidation of Sulfide to Sulfoxide

The design and synthesis of metal-organic frameworks (MOFs) as photocatalytic molecular reactors for varied reactions have drawn great attention. In this work, we designed a novel photoactive perylenediimides-based (PDI) carboxylate ligand N,N'-di(3',3",5',5"-tetrakis(4-carboxyphenyl))-1,2,6,7-tetrachloroperylene-3,4,9,10-tetracarboxylic acid diimide (Cl-PDI-TA) and use it to successfully synthesize a novel Zr(IV)-based MOF 1 constructed from [Zr6 O8 (H2 O)8 ]8+ clusters bridged by Cl-PDI-TA ligands. Structural analysis revealed that Zr-MOF 1 manifests a 3D framework with (4,8)-connected csq topology and possesses triangular channels of ~17 Å and mesoporous hexagonal channels of ~26 Å along c-axis. Moreover, the synthesized Zr-MOF 1 exhibits visible-light absorption and efficient photoinduced free radical generation property, making it a promising photocatalytic molecular reactor. When Zr-MOF 1 was used as a photocatalyst for the aerobic oxidation of sulfides under irradiation of visible light, it could afford the corresponding sulfoxides with high yield and selectivity. Experimental results demonstrated that the substrate sulfides could be fixed in the pores of 1 and directly transformed to the products sulfoxides in the solid state. Furthermore, the mechanism for the photocatalytic transformation was also investigated and the results revealed that the singlet oxygen (1 O2 ) and superoxide radical (O2 ⋅- ) generated by the energy transfer and electron transfer from the photoexcited Zr-MOF to oxidants were the main active species for the catalytic reactions. This work offers a perceptive comprehension of the mechanism in PDI-based MOFs for further study on photocatalytic reactions.

Visible-Light-Responsive Polyoxometalate@Metal-Organic Frameworks Involving Ir Metalloligands for Highly Selective Photocatalytic Oxidation of Sulfides to Sulfoxide

The synthesis of highly efficient visible-light-responsive photocatalysts is fundamental to solving the problems of low efficiency and poor selectivity in photocatalytic organic synthesis reactions. We synthesized a crystalline polyoxometalate @metal-organic framework material {Zn4 (H2 O)8 [Ir(ppy)2 (dcbpy)]4 [SiW12 O40 ]} ⋅ 4H2 O (Ir-SiW) by self-assembly of Ir metalloligands with POMs. The introduction of Ir metalloligands extends the light absorbing range to visible light, improving the efficient utilization of solar energy. The transfer of photogenerated electrons from Ir metalloligands to SiW12 was observed under visible light irradiation, which boosted the carrier separation efficiency. The synergistic effect of the two components increased the photocatalytic thioether oxidation activity, and the product methyl phenyl sulfoxide for 2.5 h under visible light irradiation (λ >400 nm) reached 99.5 %, which was higher than those of other POM-based photocatalysts. Meanwhile, the yield of methyl phenyl sulfoxide was still higher than 97 % after three cycles, demonstrating the high stability and reusability of Ir-SiW.