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

Abstract

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), {Co 4 W 22 -DPNDI}, is prepared by incorporating the unusual Co4-sandwiched POM anion [Co4(μ-OH)2(SiW11O39)2]10– ({Co 4 W 22 }) and the photoactive organic bridging link N,N′-bis­(4-pyridylmethyl)­naphthalene diimide (DPNDI) into a framework. {Co 4 W 22 } 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 {Co 4 W 22 } and DPNDI facilitate electron–hole separation and electron transfer. {Co 4 W 22 -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.

Copper-Containing Polyoxometalate-Based Metal–Organic Frameworks as Heterogeneous Catalysts for the Synthesis of N-Heterocycles

“…The Fourier transform infrared (FT-IR) spectra of CuSiW , CuPMo , and CuPW are shown in Figures S12 and S13. The bands at 1072, 963, 875, and 750 cm –1 for CuSiW should be attributed to the vibrations of Si–O a , W–O d , and W–O b/c –W in SiW 12 , respectively . For CuPMo , the vibrations of P–O a , Mo–O d , and Mo–O b/c –Mo result in the bands at 1060, 951, 871, and 756 cm –1 , respectively .…”

“…MOFs exhibit the characteristic features of the large surface area, controllable structure, modifiable pore size, and so on. − The porous natures of MOFs make them promising in the field of heterogeneous catalysts or/and excellent catalyst supports. Thus, high stability in polar solvents and high catalytic activity could be obtained by combining the characteristics of POMs and MOFs, i.e., polyoxometalate-based metal–organic frameworks (POMOFs). ,,,,− For example, Liu and co-workers reported a stable POMOF, [Cu I (bbi)] 2 {[Cu I (bbi)] 2 V IV 2 V V 8 O 26 } (bbi = 1,1′-(1,4-butanediyl)­bis­(imidazole)), which could catalyze the oxidative cleavage of lignin efficiently . Niu and co-workers reported a new POMOF [HFe 4 O 2 (H 2 O) 4 (pydc) 3 PW 12 O 40 ]·10.5H 2 O (H 2 pydc = pyridine-2,5-dicarboxylic acids), which showed outstanding heterogeneous catalytic activity for the selective oxidation of alkylbenzenes .…”

State-of-the-art advances in the syntheses, structures, and applications of polyoxometalate-based metal–organic frameworks

“…In comparison with saturated Keggin-type POM-MOFs, only a few mono-vacant Keggin-type POM-MOFs were discovered in the past decades, [90][91][92][93][94][95] which may be related to the reason that vacant sites on mono-lacunary Keggin-type POM BBs are easy to bond with oxyphilic RE or TM cations, generally resulting in purely inorganic RE-or TM-bridged polymeric POM aggregates or inorganic-organic hybrid extended frameworks with organic ligands as ornaments. [96][97][98][99] Thus, the synthesis of lacunary-POM-based MOFs remains still a great challenge.…”

“…13e). 93 The photoactive DPNDI easily transforms to DPNDI* radical species, which is helpful for activating O2. Besides, the nanoscale π-conjugated surfaces of DPNDI also have the ability to facilitate the electron-hole separation and electron transfer during the photocatalytic process, which significantly increases…”

Two Polyoxometalate-Encapsulated Two-Fold InterpenetratingdiaMetal–Organic Frameworks for the Detection, Discrimination, and Degradation of Phenolic Pollutants

“…However, because of their discrete molecular cluster structures and high solubility, POMs generally have surface areas of less than 10 m 2 ·g –1 and show low recyclability as photocatalysts, which seriously restrict their application. To overcome these bottlenecks, polyoxometalate-based functional complexes − have been studied and widely used in photocatalysis, electrocatalysis, and other fields. Among various POM-based functional materials, polyoxometalate-based metal–organic frameworks (POMOFs), − which are constructed by introducing POMs as guest molecules into metal–organic framework hosts, have gained the attention of chemists. − Consequently, the surface areas, stability, and conductivity of resulting POMOFs are significantly improved.…”