A Thiophene-2-carboxamide-Functionalized Zr(IV) Organic Framework as a Prolific and Recyclable Heterogeneous Catalyst for Regioselective Ring Opening of Epoxides.

A new thiophene-2-carboxamide-functionalized Zr-UiO-66 MOF (1) was synthesized by employing a traditional solvothermal procedure. Compound 1 displayed high thermal (up to 340 °C under an Ar atmosphere) and chemical stability (in water, 1 M HCl, and acetic acid). A nitrogen physisorption measurement with the activated form of 1 (denoted 1') exhibited a BET surface area (781 m2/g) despite attachment of a bulky side chain with the linker molecule. Compound 1' was able to heterogeneously catalyze the ring-opening reaction of epoxides with  amines. Catalyst 1' exhibited significant yields as well as wide substrate scope in the ring opening of epoxides by means of amines. It also displayed better catalytic performance in comparison to known MOF catalysts such as Cu3(BTC)2, Fe(BTC) (BTC: 1, 3, 5-benzenetricarboxylate), and Zr-UiO-66. Control experiments were performed with free linker,  Zr(IV) salt and without catalyst 1', confirming the exclusive role of 1' in the catalytic reaction. The reusability characteristics of catalyst 1' was established for up to five consecutive catalytic cycles. The synthesis and characterization of the linker molecule, material 1, and 1' and mechanism of the catalysis reaction were studied elaborately.

A functionalized UiO-66 MOF for turn-on fluorescence sensing of superoxide in water and efficient catalysis for Knoevenagel condensation.

In the present work, a new MOF material of the UiO-family called Zr-UiO-66-NH-CH2-Py (1) has been obtained by the solvothermal technique and successfully characterized. The MOF structure was assembled with 2-((pyridin-4-ylmethyl) amino) terephthalic acid (H2BDC-NH-CH2-Py) as linker and Zr4+ ion. The activated form of 1 (called 1') exhibits considerable thermal and chemical stability. Compound 1' showed a very rapid and selective response for the fluorometric sensing of superoxide (O2·-) in aqueous medium even in the presence of the potentially competitive reactive oxygen species (ROS). The limit of detection value for O2·- sensing is 0.21 µM, which is comparable with those of the reported O2·- sensors. This is the first MOF based fluorescent sensor for the detection of O2·-. The response time of this MOF sensor for O2·- is very short (240 s). On the other hand, 1' was employed as a solid heterogeneous catalyst for Knoevenagel condensation between benzaldehyde and ethyl cyanoacetate at 80 °C in ethanol resulting in a very high yield of the desired product. The effects of the esterified linker ((CH3)2BDC-NH-CH2-Py) and the corresponding metal salt (ZrCl4) on this catalytic reaction were examined separately. We have also tested the substrate scope elaborately for the catalytic reaction promoted by catalyst 1'.

Highly Active Urea-Functionalized Zr(IV)-UiO-67 Metal-Organic Framework as Hydrogen Bonding Heterogeneous Catalyst for Friedel-Crafts Alkylation.

A new Zr(IV)-based UiO-67 metal-organic framework (1) was prepared with urea-functionalized biphenyl-4,4'-dicarboxylic acid (BPDC-urea) as the linker using conventional solvothermal technique and thoroughly characterized using X-ray powder diffraction (XRPD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric (TG), and N2 sorption analyses. The activated form of 1 (called 1') exhibited excellent BET surface area in spite of having a large functional moiety (urea) in the linker side. The activated form of this material (1') was successfully employed for the Friedel-Crafts alkylation of indole with ß-nitrostyrene to achieve 97% yield in toluene at 70 °C for 24 h. Furthermore, the catalyst was used for four cycles, with no significant loss in its activity, and the reaction was heterogeneous in nature. The activity of 1' was comparable to UiO-67-(NH2)2, whereas the activity was 2-fold higher compared to the parent UiO-67. Further, the activity of the BPDC-urea linker was nearly 2-fold higher than that of ZrCl4, suggesting the crucial role played by the urea moiety than the metal node. In addition, the catalyst (1') exhibited a wide substrate scope, allowing the preparation of a series of compounds with moderate to high yields under the optimized reaction conditions. The roles of metal salt and linker in the catalysis have also been studied separately, and the mechanism for the catalysis has been clarified.

Cu3(BTC)2 catalyzed dehydrogenative coupling of dimethylphenylsilane with phenol and homocoupling of dimethylphenylsilane to disiloxane.

Cu3(BTC)2 (BTC: 1,3,5-benzenetricarboxylic acid) showed to be an efficient and reusable heterogeneous solid catalyst for the formation of SiO bond through dehydrogenative coupling of dimethylphenylsilane (1) with phenol under mild reaction conditions. It is observed that Fe(BTC), MIL-101(Cr) and UiO-66(Zr) are not able to promote this cross coupling between 1 and phenol. Cu3(BTC)2 exhibits higher stability and activity compared to other MOFs studied here. Furthermore, Cu3(BTC)2 is reused for three consecutive cycles with a slight decay in its activity. Comparison of the powder XRD patterns of the fresh with three times used Cu3(BTC)2 showed no significant difference in the crystalline structure, thus, indicating the catalyst stability under the optimized reaction conditions. Furthermore, EPR, FT-IR and SEM images of the fresh and reused Cu3(BTC)2 did not show any change in the oxidation state of copper or structural morphology. Also, no leaching of copper is detected under optimized reaction conditions. In addition, Cu3(BTC)2 showed higher activity compared to Pt, Pd, Au and Cu supported on active carbon as heterogeneous catalysts in the synthesis of disiloxane from 1 through SiH activation.