A porous organic cage composed of six iron tetraphenylporphyrins was used as a supramolecular catalyst for electrochemical CO -to-CO conversion. This strategy enhances active site exposure and substrate diffusion relative to the monomeric catalyst, resulting in CO generation with near-quantitative Faradaic efficiency in pH 7.3 water, with activities reaching 55 250 turnovers. These results provide a starting point for the design of supramolecular catalysts that can exploit the properties of the surrounding matrix yet retain the tunability of the original molecular unit.
We report here a synthetic ion channel developed from a shape-persistent porphyrin-based covalent organic cage. The cage was synthesized by employing a synthetically economical dynamic covalent chemistry (DCC) approach. The organic cage selectively transports biologically relevant iodide ions over other inorganic anions by a dehydration-driven, channel mechanism as evidenced by vesicle-based fluorescence assays and planar lipid bilayer-based single channel recordings. Furthermore, the organic cage appears to facilitate iodide transport across the membrane of a living cell, suggesting that the cage could be useful as a biological tool that may replace defective iodide channels in living systems.
We report a supramolecular strategy for promoting the selective reduction of O2 for direct electrosynthesis of H2O2. We utilized cobalt tetraphenylporphyrin (Co‐TPP), an oxygen reduction reaction (ORR) catalyst with highly variable product selectivity, as a building block to assemble the permanently porous supramolecular cage Co‐PB‐1(6) bearing six Co‐TPP subunits connected through twenty‐four imine bonds. Reduction of these imine linkers to amines yields the more flexible cage Co‐rPB‐1(6). Both Co‐PB‐1(6) and Co‐rPB‐1(6) cages produce 90–100 % H2O2 from electrochemical ORR catalysis in neutral pH water, whereas the Co‐TPP monomer gives a 50 % mixture of H2O2 and H2O. Bimolecular pathways have been implicated in facilitating H2O formation, therefore, we attribute this high H2O2 selectivity to site isolation of the discrete molecular units in each supramolecule. The ability to control reaction selectivity in supramolecular structures beyond traditional host–guest interactions offers new opportunities for designing such architectures for a broader range of catalytic applications.
Mechanically interlocked structures, such as catenanes and rotaxanes, are fascinating synthetic targets and some are used for molecular switches and machines. Today, the vast majority of catenated structures are built upon macrocycles and only a very few examples of three-dimensional shape-persistent organic cages forming such structures have been reported. However, the catenation in all these cases was based on a thermodynamically favoured π–π-stacking under certain reaction conditions. Here, we show that catenane formation can be induced by adding methoxy or thiomethyl groups to one of the precursors during the synthesis of chiral [8 + 12] imine cubes, giving dimeric and trimeric catenated organic cages. To elucidate the underlying driving forces, we reacted 11 differently 1,4-disubstituted terephthaldehydes with a chiral triamino tribenzotriquinacene under various conditions to study whether monomeric cages or catenated cage dimers are the preferred products. We find that catenation is mainly directed by weak interactions derived from the substituents rather than by π-stacking.
Ap orous organic cage composed of six iron tetraphenylporphyrins was used as as upramolecular catalyst for electrochemical CO 2 -to-CO conversion. This strategy enhances active site exposure and substrate diffusion relative to the monomeric catalyst, resulting in CO generation with near-quantitative Faradaic efficiency in pH 7.3 water,w ith activities reaching 55 250 turnovers.T hese results provide astarting point for the design of supramolecular catalysts that can exploit the properties of the surrounding matrix yet retain the tunability of the original molecular unit.Electrochemical CO 2 reduction is an attractive approach to developing energy-efficient CO 2 fixation processes,b ut such systems necessitate selective product generation over longterm electrolysis at low overpotential. [1] In this context, water is an abundant and benign proton source for CO 2 reduction; however, it can promote catalyst degradation and off-target H 2 evolution. Materials catalysts can exhibit aqueous compatibility,b ut often are difficult to tune for selectivity owing to shortcomings in molecular-level control. [2] Homogeneous molecular catalysts can reduce CO 2 into value-added products such as CO [3] yet often require organic solvent. CO 2 reduction by water-soluble catalysts is rare, [4] but methods for catalyst immobilization [5] or deposition [6] onto an electrode can permit the use of aqueous electrolytes.Assuch, we have initiated ap rogram using multiple approaches for electrochemical carbon fixation that integrate tunable molecular catalysts into hybrid materials to endow aqueous stability and to organize catalysts at the electrode so as to encourage productive interactions with the substrate. [7] Against this backdrop,w ew ere inspired by supramolecular vessels for catalysis wherein control of the spatial arrangement of both catalyst and substrate is emphasized. [8] In this group,porous organic cages (POCs) are unique hybrid structures that combine molecular tunability and solubility with materials-like structural porosity. [9] These cages are built from subunits connected through covalent linkages to form an inner cavity without the high charge buildup associated with metal-templated vessels [10] that could complicate electrochemical behavior,m aking such applications rare, [11] especially in electrocatalysis. [8g] POCs can possess large surface areas, [12] exhibit high chemical stability, [12b,13] and be easily processed owing to their solubility. [14] Advances in POC synthesis have enabled applications in host-guest chemistry, [15] gas uptake and separation, [16] nanoparticle synthesis, [17] porous additives in materials, [18] liquids, [19] and cell membranes, [20] as well as building blocks in extended frameworks [21] and polymers. [22] Herein, we install iron tetraphenylporphyrin (Fe-TPP), an established catalyst for the electroreduction of CO 2 to CO, into ar hombicuboctahedral POC to increase the electrochemically active surface area and facilitate mass transport (Scheme 1). Thep orphyrin box (PB) was synthe...
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