Metal-organic frameworks (MOFs) decorated with stable organic radicals are highly promising materials for redox catalysis. Unfortunately however, the synthesis of chemically robust MOFs typically requires harsh solvothermal conditions, which are not compatible with organic radicals. Here we describe the synthesis of two isoreticular families of stable, mixed-component, zirconium MOFs with UiO-66 and UiO-67 structure and controlled amounts of covalently attached TEMPO radicals. The materials were obtained using a relatively low-temperature, HCl-modulated de novo method developed by Hupp and Farha and shown to contain large amounts of missing cluster defects, forming nanodomains of reo phase with 8-connected clusters. In the extreme case of homoleptic UiO-67-TEMPO(100%), the material exists as an almost pure reo phase. Large voids due to missing clusters and linkers allowed these materials to accommodate up to 2 times more of bulky TEMPO substituents than theoretically predicted for the idealized structures and proved to be beneficial for catalytic activity. The TEMPO-appended MOFs were shown to be highly active and recyclable catalysts for selective aerobic oxidation of a broad range of primary and secondary alcohols under exceptionally mild conditions (RT, atmospheric pressure of air). The influence of various parameters, including pore size and TEMPO content, on the catalytic activity was also comprehensively investigated.
A versatile method for the post-synthetic removal of primary amino groups from metal-organic frameworks (MOFs) has been developed. The method allowed the first successful synthesis of the missing parent compound of an important family of MOFs – the unsubstituted (Al)MIL-101. The material was shown to be a useful reference compound for the elucidation of the role of amino groups in the adsorption and deactivation of olefin metathesis catalysts. The chemoselectivity of the deamination is sufficient for the selective removal of NH2 substituents from mixed-linker MOFs bearing both NH2 and RCONH groups.
Joining together two diamidocarbazole moieties with a flexible linker led to a selective fluorescent sensor for an extremely hydrophilic sulfate anion, which works even in the presence of 25% of water! It allowed sulfate detection in real world samples, such as mineral waters, which contain many other anions. See more.
Diaminocarbazole was also used to construct a new catalytic system, composed of bimetallic Au@Pt nanoparticles dispersed in a conducting polymer. Our new organic-inorganic hybrid system shows enhanced activity towards formic acid electrooxidation. See more.
Despite their record-braking sorption capacities, metal−organic frameworks (MOFs) have rarely been used for the immobilization of homogeneous catalysts by simple absorption from solution. Here we demonstrate that this simple strategy allows the first successful immobilization of olefin metathesis catalysts inside MOFs. Ruthenium alkylidene complexes bearing ammonium-tagged NHC ligands were successfully supported inside (Al)MIL-101-NH2·HCl. The materials thus obtained are true heterogeneous catalysts, active toward various substrates with TONs up to 8900 (in batch conditions) or 4700 (in continuous flow). Although the catalysts were held inside the MOF by noncovalent forces only, leaching was not observed and heavy metal contamination of the products was found to be below the detection limit of ICP MS (0.02 ppm). The robustness of the catalyst attachment allowed their use in a continuous flow setup.