Adenine-Based Zn(II)/Cd(II) Metal–Organic Frameworks as Efficient Heterogeneous Catalysts for Facile CO₂ Fixation into Cyclic Carbonates: A DFT-Supported Study of the Reaction Mechanism

Abstract

We synthesized two new adenine-based Zn-(II)/Cd(II) metal−organic frameworks (MOFs), namely, [Zn 2 (H 2 O)(stdb) 2 (5H-Ade)(9H-Ade) 2 ] n (PNU-21) and [Cd 2 (Hstdb)(stdb)(8H-Ade)(Ade)] n (PNU-22), containing auxiliary dicarboxylate ligand (stdb = 4,4′-stilbenedicarboxylate). Both MOFs were characterized by multiple analytical techniques such as single-crystal X-ray diffraction (SXRD), powder X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscopy, as well as temperature program desorption and Brunauer−Emmett−Teller measurements. Both MOFs were structurally robust and possessed unsaturated Lewis acidic metal centers [Zn(II) and Cd(II)] and free basic N atoms of adenine molecules. They were used as heterogeneous catalysts for the fixation of CO 2 into five-membered cyclic carbonates. Significant conversion of epichlorohydrin (ECH) was attained at a low CO 2 pressure (0.4 MPa) and moderate catalyst (0.6 mol %)/cocatalyst (0.3 mol %) amounts, with over 99% selectivity toward the ECH carbonate. They showed comparable or even higher catalytic activity than other previously reported MOFs. Because of high thermal stability and robust architecture of PNU-21/PNU-22, both catalysts could be reused with simple separation up to five successive cycles without any considerable loss of their catalytic activity. Densely populated acidic and basic sites in both Zn(II)/Cd(II) MOFs facilitated the conversion of ECH to ECH carbonate in high yields. The reaction mechanism of the cycloaddition reaction between ECH and CO 2 is described by possible intermediates, transition states, and pathways, from the density functional theory calculation in correlation with the SXRD structure of PNU-21.

New Supercage Metal–Organic Framework Based on Allopurinol Ligands Showing Acetylene Storage and Separation

“…It is well knownt hat adenine which contains the strong coordinated ability of N-heterocycle (pyrimidine and imidazole) and -NH 2 group is very magnetic in constructing biological MOFsw ith stabilitya nd variousf unctions (Scheme S1). [23][24][25][26][27][28][29] Allopurinol (ALP), named1 ,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one, is an important medicine for healing gout and belongst oap urine analog that consists of ap yrimidine ring fused to an pyrazoler ing. Comparedt oa denine, ALP is also planara nd N-rich, but contains different pyrazole ring and carbonyls ites as well as potential À2c harge valence, while adenine has no carbonyl site and is À1c harge in MOFs.S oi t wouldb ev ery deserving excepted to exploret he coordination chemistry of ALP in MOF fabrication.…”

Three Lanthanide Metal‐Organic Frameworks Based on an Ether‐Decorated Polycarboxylic Acid Linker: Luminescence Modulation, CO2 Capture and Conversion Properties

“…As shown in Table , 1‐Eu shows effective catalytic activity for the cycloaddition reaction of CO 2 with PO, with a conversion of 82.7 % within 48 hours (Table , entry 3). This valve is moderately high, and exceeds some reported vales . In contrast, the individual catalytic efficiency of 1‐Eu or TBAB for PO was very low (Table , entries 1 and 2).…”

“…This valve is moderately high, and exceeds some reported vales. [52][53][54][55][56] In contrast, the individual catalytic efficiency of 1-Eu or TBAB for PO was very low (Table 1, entries 1and 2).…”

Metal–organic frameworks for chemical conversion of carbon dioxide

“…The adenine-based MOFs formed by auxiliary dicarboxylates and unsaturated Lewis acidic metal centers Zn(II) and Cd(II) allow to get a significant conversion of epichlorohydrin at a low CO 2 pressure (0.4 MPa) with a moderate catalyst (0.6 mol%)/co-catalyst (0.3 mol%) amounts, the selectivity being over 99% toward the ECH carbonate. 25 Also, defects in the MOF structure and/or the defects on the MOF surface can catalyze the cycloaddition of epoxide with CO 2 when the linkers are not catalytically active and the metal centers are coordinatively saturated. In most of the cases, the MOFs are Zn 2 + -containing materials.…”