Porphyrin–Polyoxotungstate Molecular Hybrid as a Highly Efficient, Durable, Visible-Light-Responsive Photocatalyst for Aerobic Oxidation Reactions

Abstract

Organic−polyoxometalate (POM) hybrids have recently attracted considerable interest because of their distinctive properties and wide-ranging applications. For the construction of organic−POM hybrids, porphyrins are promising building units owing to their optical properties and reactivity, including strong visible-light absorption and subsequent singlet-oxygen ( 1 O 2 *) generation. However, the practical utilization of porphyrins as photocatalysts and photosensitizers is often hindered by their own degradation by 1 O 2 *. Therefore, there is a substantial demand for the development of porphyrin-derived photocatalysts with both high efficiency and durability. Herein, we present a porphyrin− polyoxotungstate molecular hybrid featuring a face-to-face stacked porphyrin dimer (I) fastened by four lacunary polyoxotungstates. Hybrid I exhibited remarkable efficiency and durability in photocatalytic aerobic oxidation reactions, and the selective oxidation of various dienes, alkenes, sulfides, and amines proceeded using just 0.003 mol % of the catalyst. Mechanistic investigations suggested that the high activity of I stems from the efficient generation of 1 O 2 *, resulting from the heavy-atom effect of POMs. Furthermore, despite its high efficiency in 1 O 2 * generation compared to free porphyrins, I exhibited superior durability against 1 O 2 *-induced degradation under photoirradiation.

Polyoxometalate‐Based Frameworks: Construction Strategies and Photocatalytic Applications

“…POMs-based frameworks also exhibit outstanding heterogeneous photocatalytic activity for the selective organic synthesis, due to the remarkable oxidation capacity of POMs, such as oxidative coupling of alkenes, oxidation of sulfides, alcohols to aldehydes, CÀ C coupling reaction. [70,71] (ZnWÀ PYI), using the [PZnW 11 O 39 ] 5À anion, Zn 2 + and chiral amino catalyst PYI, which generated in situ from 5-bromo-4-chloro-3-indolyl phosphate. [72] The synthesis of imines from alkenes and amines using ZnWÀ PYI was investigated employing pyrrolidine as an organic catalyst and O 2 as an oxidant.…”

Rare-Earth Metal–Organic Framework with Nonplanar Porphyrin Groups for High-Efficiency Photocatalysis

“…A large number of studies have demonstrated their great potential in many applications, such as gas adsorption, separation, catalysis, proton conductivity, − etc. Among them, porphyrinic metal–organic frameworks (PMOFs), a special class of MOFs constructed by porphyrin-derived ligands, have attracted considerable attention because of their outstanding properties in photocatalysis, sensing, and biomedical applications. − Though many PMOFs with different structures have been reported, the porphyrin macrocycle in these PMOFs mostly exhibited a regular planar conformation due to its conjugated nature with high stability, as found in the most used porphyrinic ligands, like tetrakis­(4-carboxyphenyl)­porphyrin (TCPP) − and 5,10,15,20-tetrakis­(4-pyridyl)­porphine (TPyP). , Therefore, the construction of PMOFs with porphyrin cores in out-of-plane distortion is highly desirable but remains a great challenge.…”

Self-assembled molecular hybrids comprising lacunary polyoxometalates and multidentate imidazole ligands

“…Recently, our research group reported that pyridine-based ligands are effective for constructing POM–organic hybrids via reversible coordination bonds between pyridine and the vacant sites of lacunary POMs. 8 Three pyridine molecules can coordinate with the Mo atoms at the vacant sites of a trivacant lacunary Keggin-type phosphomolybdate (TBA 3 H 6 [A-α-PMo 9 O 34 ], TBA = tetra- n -butylammonium) to form TBA 3 [A-α-PMo 9 O 31 (pyridine) 3 ]. Moreover, we found that this pyridine-coordinated hybrid can be reacted with multidentate pyridine-based ligands in organic solvents to synthesize more complex molecular hybrids via ligand exchange reactions.…”

“…Moreover, we found that this pyridine-coordinated hybrid can be reacted with multidentate pyridine-based ligands in organic solvents to synthesize more complex molecular hybrids via ligand exchange reactions. 8 …”