Highly Efficient Supramolecular Catalysts Assembled by Dawson-Type POMs and Metal–Organic Complexes for the Synergistic Catalytic Synthesis of p-Benzoquinones

Abstract

Selective oxidation of alkyl-substituted phenols offers an ideal pathway to synthesize p-benzoquinones (p-BQs), but it is known to be inefficient because of the parallel competing reactions. Aiming at the design and synthesis of more powerful heterogeneous catalysts for highly efficient synthesizing functionalized p-BQs, herein, we report two crystalline catalysts with supramolecular networks based on Dawson-type polyoxometalates 2), where ptz = 5-(4-pyridyl)-1H-tetrazole and ina = isonicotinic acid. Structural analysis shows that 1 is formed by the supramolecular contact between one-dimensional POM inorganic chains and two kinds of trinuclear Cu-organic clusters, while 2 is formed by supramolecular stacking of ladder-like one-dimensional chains that are composed of ribbonlike nonanuclear Cu-organic clusters and POM anions. Both supramolecular catalysts exhibit high catalytic activity in H 2 O 2 -based oxidation of phenols/aromatics to p-BQs. Strikingly, in the synthesis of trimethyl-p-benzoquinone (TMBQ, an intermediate of vitamin E) by oxidizing 2,3,6trimethylphenol, the conversion, selectivity, and oxidant efficiency can reach >99, 97.9, and 85.0% for 1, as well as 95.4, >99, and 79.8% for 2 within 5 min, respectively. Also, the catalytic activities of 1 and 2 presented by the turnover frequency are 12 000 (the highest thus far) and 7632 h −1 , respectively. Detailed structure−activity analysis revealed that the higher performance of 1 is attributed to the more active-site accessibility due to the supramolecular interactions between POM and Cu organic units in the framework. Moreover, the observed yield of TMBQ has not decreased and the skeleton of catalysts has not changed in >10 cycles. The reaction mechanism was also systematically studied, and the parallel dual center, namely, Cu-site and POM, -driven reaction processes (radical and oxygen transfer) were illuminated.

Screening 0D Materials for 2D Nanoelectronics Applications

“…is Sb 2 O 3 (656 °C), that was already previously identified. [ 10,11 ] The atomic structure consists of Sb 4 O 6 cages, similar to C 10 H 16 carbon cages, called adamantane, but without terminating H. There are few materials with higher dielectric constant, such as HgBr, HgCl, and Re 2 H 4 O 9 , but those have also lower band gap and lower melting point. Moreover, although HgBr and HgCl have fairly high mp., they are unfortunately highly toxic.…”

“…Recently, formation of 2D molecular crystal was demonstrated from Sb 2 O 3 0D material, that is, a material consisting of weakly bound small molecular units with no dangling bonds. [ 10 ] Using these as a substrate or gate dielectric in 2D material field‐effect transistors resulted in high mobility, small hysteresis, low density of trap states, and high subthreshold slope. [ 11 ] The authors called for theoretical studies to find more suitable 0D material candidates.…”

Giant Tunability of Charge Transport in 2D Inorganic Molecular Crystals by Pressure Engineering

“…Among these three phases, α‐Sb 2 O 3 is a molecular crystal (space group Fd $$\bar 3$$ m ) composed of the Sb 4 O 6 molecular cage with T d point group symmetry, [10] as depicted in Figure 1a. Given the characteristic of molecular crystal and good thermal stability of α‐Sb 2 O 3 , [11] vertical micro‐spacing sublimation (VMS) strategy (Figure 1b) was utilized to grow 2D α‐Sb 2 O 3 flakes, which possesses the advantages of low‐cost, simple operation and short growth time in comparison with the conventional chemical vapor deposition (CVD) methods [1b, 12] . Detailed growth method is provided in the section of experiment details in the Supporting Information.…”

“…It should be emphasized that here, 2DIMCs possess unique structural features and are distinct from 2D atomic crystals as well as 2D organic molecular crystals [1a, b, e] . For 2D atomic crystals, each layer is formed by atoms, which are connected by strong covalent bonds; whereas in 2DIMCs, each layer is composed of inorganic molecules, which are bonded together through weak van der Waals (vdW) force [1e] .…”

“…Two‐dimensional inorganic molecular crystals (2DIMCs) have emerged as rising stars due to their unique structure and exceptional physical properties, including long‐range molecular ordering, diverse molecular structure, excellent dielectric property, and high thermal stability [1] . Unfortunately, due to the weak intermolecular coupling, they typically show poor charge transport and behave as insulators, severely hindering their potential applications in electronics and optoelectronics [1b, 2] . Their intrinsic poor charge transport property is promising to be addressed by applying compressive strain [3] .…”