Functionalization of Metal–Organic Frameworks through the Postsynthetic Transformation of Olefin Side Groups

Abstract

For the first time, the adaptability of the C=C double bond as a versatile precursor for the postsynthetic modification (PSM) of microporous materials was extensively investigated and evaluated. Therefore, an olefin-tagged 4,4'-bipyridine linker was synthesized and successfully introduced as pillar linker within a 9,10-triptycenedicarboxylate (TDC) zinc paddle-wheel metal-organic framework (MOF) through microwave-assisted synthesis. Different reactions, predominately used in organic chemistry, were tested, leading to the development of new postsynthetic reactions for the functionalization of solid materials. The postsynthetic oxidation of the olefin side groups applying osmium tetroxide (OsO₄) as a catalyst led to the formation of a microporous material with free vicinal diol functionalities. The epoxidation with dimethyldioxirane (DMDO) enabled the synthesis of epoxy-functionalized MOFs. In addition to that, reaction procedures for a postsynthetic hydroboration with borane dimethyl sulfide as well as a photoinduced thiol-ene click reaction with ethyl mercaptan were developed. For all of these PSMs, yields of more than 90% were obtained, entirely maintaining the crystallinity of the MOFs. Since the direct introduction of the corresponding groups by means of pre-synthetic approaches is hardly possible, these new PSMs are useful tools for the functionalization of porous solids towards applications such as selective adsorption, separation, and catalysis.

Gated Channels and Selectivity Tuning of CO2 over N2 Sorption by Post‐Synthetic Modification of a UiO‐66‐Type Metal–Organic Framework

“…Both bromination with elemental bromine and a UV‐initiated thiol‐ene click reaction using ethyl mercaptane proceeded in nearly quantitative yields and good conversions of the double bond, which were comparable to the results of our previous work . Although crystallinity was retained in both cases according to PXRD, the accessible BET surface area of the activated samples dropped to 5 and 52 m 2 g −1 , respectively.…”

Postsynthetic Modification of Metal‐Organic Frameworks through Click Chemistry

“…Rieger et al [67] reported an olefinfunctional MOF, in which the adaptability of the C＝C double bond for PSM was extensively investigated and evaluated. Until now, there are only two examples regarding to PSM of MOFs via thiol-ene reaction.…”

Pore surface engineering in a zirconium metal–organic framework via thiol-ene reaction

“…In principle, it can also be applied to covalently attach functional groups within the framework of MOFs. However, to our surprise, the thiol-ene reaction had only been utilized to chemically tailor the pore surface of an olefin-tagged Zn paddle-wheel MOF until recently [13]. In this manuscript, we reported the second example of the PSM of MOF through thiol-ene reaction.…”

“…1 H NMR (300 MHz, CDCl 3 , ppm): δ¼8.11 (d, J ¼7.9 Hz, 4H), 7.66 (d, J ¼7.9 Hz, 4H), 6.99 (s, 2H), 3.95 (s, 6H), 3.81 (s, 6H). 13 C NMR (75 MHz, CDCl 3 , ppm): δ¼167.0, 150.7, 142.8, 130.0, 129.43, 129.39, 128.8, 114.5, 56.4, 52 Synthesis of 5: A solution of compound 4 (253 mg, 0.72 mmol) in dry DMF (20 mL) was treated with potassium carbonate (540 mg, 3.9 mmol) and ally bromide (0.6 mL, 6.94 mmol) under N 2 . The resulting reaction mixture was heated at 80 1C for 60 h before H 2 O (50 mL) was added.…”