Influence of functionalization of terephthalate linker on the catalytic activity of UiO-66 for epoxide ring opening

Abstract

A series of five isostructural zirconium terephthalate UiO-66 metal organic frameworks bearing different functional groups on the terephthalate linker (UiO-66-X; X = H, NH2, NO2, Br, Cl,) have been successfully prepared and characterized. UiO-66-X materials were evaluated as heterogeneous catalysts for the epoxide ring opening of styrene oxide by methanol, observing an increase in the initial reaction rate from UiO-66-H to UiO-66-Br, over one order of magnitude. The reactivity order, however, does not follow a linear relationship between the Hammett constant value of the substituent and the initial reaction rate. UiO-66-Br exhibits a wide scope, its activity depending on the structure of epoxide and nucleophile. The absence of Zr leaching to the solution together with the preservation of the UiO-66-X crystallinity confirms the stability of the framework under the reaction conditions. Nevertheless, UiO-66 undergoes a progressive deactivation upon reuse that was attributed to a strong adsorption of the reaction product.

Engineering UiO‐66 Metal Organic Framework for Heterogeneous Catalysis

“…[82] The initial reaction rate observed at 50°C for UiO-66-H, UiO-66-NO 2 , UiO-66-NH 2 , UiO-66-Br and UiO-66-Cl were 9.6, 20, 50.1, 143.1 and 128.8 (mol À 1 ) × 10 À 6 , respectively, which is an increase in the initial reaction rate from UiO-66-H to UiO-66-Br, over one order of magnitude. [82] The initial reaction rate observed at 50°C for UiO-66-H, UiO-66-NO 2 , UiO-66-NH 2 , UiO-66-Br and UiO-66-Cl were 9.6, 20, 50.1, 143.1 and 128.8 (mol À 1 ) × 10 À 6 , respectively, which is an increase in the initial reaction rate from UiO-66-H to UiO-66-Br, over one order of magnitude.…”

Lead‐Free Cs3Bi2Br9 Perovskite as Photocatalyst for Ring‐Opening Reactions of Epoxides

“…Based on related literature, we hypothesized that the surface of our Cs 3 Bi 2 Br 9 photocatalyst contained the acid sites needed for epoxide activation. To investigate this, we performed UV/Vis diffuse reflectance spectroscopy (DRS) analysis with alizarin as the adsorbate, which has been reported to accurately assess the surface acidity of metal oxides and sulfides .…”

“…Meanwhile, the Bi‐based Lewis‐acid sites on the photocatalyst activate the epoxide (e.g., styrene oxide) by coordinating the basic oxygen atom in the three‐membered heterocyclic ring of the epoxide . Finally, the desired alcoholysis product is generated by the backside attack of the activated epoxide by the alcohol radicals or anions through the traditional nucleophilic substitution reaction pathway …”

“…[15] Up to now,most effective heterogeneous systems reported to successfully catalyze epoxide alcoholysis reactions use corrosive, strong acids (e.g.,t riflic acid/silica) [16] or solid acids (e.g.,s ulfated Zr-HTiNbO 5 ), [17] which can result in corrosion of equipment or acid-leaching problems. Strong-acid-free catalysts (e.g.,F e III complex/SBA-15 [18] and metal-organicf rameworks such as UiO-66 [19] and Zr-MOF) [20] require harsh reactionc onditions (e.g.,h igh temperature and long reactiont ime) to obtain good conversions, which can reduce the catalyst lifetimeand present challenges for recyclability. [16] In contrast, photocatalyst-enabled organic synthesis is considered ap romising approach because it can be performed through the use of green and sustainable solar energy under mild conditions (e.g.,r oom temperature and ambient pressure).…”

MOFs vs. zeolites: carbonyl activation with M(iv) catalytic sites

“…In fact, the coordinatively unsaturated 47 The increase in the density (Figure 9b) or strength ( Figure 9c) of those sites can be tuned by the functional group present in the benzene ring of the linker, as described for the isomerization of citronellal and epoxide ring opening. 9,48 From Table 7 it is deduced that the defective Zr-UiO MOFs are, in general, more active than the zeolites described in the esterification of levulinic acid with n-butanol (entries 1-4 vs entries 5-6). Interestingly, the Zr(IV) Lewis acid sites in a high silica Beta zeolite does not improve the activity for the esterification of fatty acids with respect to the defective nano-sized The hybrid MOF material was used in at least seven reaction cycles, showing only a small decrease in the final testosterone ester yield (from 99 to 77%).…”