We report here the synthesis of a robust and porous metal-organic framework (MOF), Zr-TPDC, constructed from triphenyldicarboxylic acid (HTPDC) and an unprecedented Zr secondary building unit (SBU): Zr(μ-O)(μ-OH)(μ-OH). The Zr-SBU can be viewed as an inorganic node dimerized from two commonly observed Zr clusters via six μ-OH groups. The metalation of Zr-TPDC SBUs with CoCl followed by treatment with NaBEtH afforded a highly active and reusable solid Zr-TPDC-Co catalyst for the hydrogenation of nitroarenes, nitriles, and isocyanides to corresponding amines with excellent activity and selectivity. This work highlights the opportunity in designing novel MOF-supported single-site solid catalysts by tuning the electronic and steric properties of the SBUs.

Nanoscale metal−organic frameworks (nMOFs) have shown great potential as nanophotosensitizers for photodynamic therapy (PDT) owing to their high photosensitizer loadings, facile diffusion of reactive oxygen species (ROSs) through their porous structures, and intrinsic biodegradability. The exploration of nMOFs in PDT, however, remains limited to an oxygen-dependent type II mechanism. Here we report the design of a new nMOF, Ti-TBP, composed of Ti-oxo chain secondary building units (SBUs) and photosensitizing 5,10,15,20-tetra(p-benzoato)porphyrin (TBP) ligands, for hypoxia-tolerant type I PDT. Upon light irradiation, Ti-TBP not only sensitizes singlet oxygen production, but also transfers electrons from excited TBP* species to Ti 4+based SBUs to afford TBP •+ ligands and Ti 3+ centers, thus propagating the generation of superoxide, hydrogen peroxide, and hydroxyl radicals. By generating four distinct ROSs, Ti-TBP-mediated PDT elicits superb anticancer efficacy with >98% tumor regression and 60% cure rate. Communication pubs.acs.org/JACS

We report here the design of two multifunctional metal−organic frameworks (MOFs), mPT-Cu/Co and mPT-Cu/Re , comprising cuprous photosensitizers (Cu-PSs) and molecular Co or Re catalysts for photocatalytic hydrogen evolution (HER) and CO2 reduction (CO2RR), respectively. Hierarchical organization of Cu-PSs and Co/Re catalysts in these MOFs facilitates multielectron transfer to drive HER and CO2RR under visible light with an HER turnover number (TON) of 18 700 for mPT-Cu/Co and a CO2RR TON of 1328 for mPT-Cu/Re, which represent a 95-fold enhancement over their homogeneous controls. Photophysical and electrochemical investigations revealed the reductive quenching pathway in HER and CO2RR catalytic cycles and attributed the significantly improved performances of MOFs over their homogeneous counterparts to enhanced electron transfer due to close proximity between Cu-PSs and active catalysts and stabilization of Cu-PSs and molecular catalysts by the MOF framework.

The synthesis of highly acidic metal−organic frameworks (MOFs) has attracted significant research interest in recent years. We report here the design of a strongly Lewis acidic MOF, ZrOTf-BTC, through two-step transformation of MOF-808 (Zr-BTC) secondary building units (SBUs). Zr-BTC was first treated with 1 M hydrochloric acid solution to afford ZrOH-BTC by replacing each bridging formate group with a pair of hydroxide and water groups. The resultant ZrOH-BTC was further treated with trimethylsilyl triflate (Me 3 SiOTf) to afford ZrOTf-BTC by taking advantage of the oxophilicity of the Me 3 Si group. Electron paramagnetic resonance spectra of Zr-bound superoxide and fluorescence spectra of Zr-bound Nmethylacridone provided a quantitative measurement of Lewis acidity of ZrOTf-BTC with an energy splitting (ΔE) of 0.99 eV between the π x * and π y * orbitals, which is competitive to the homogeneous benchmark Sc(OTf) 3 . ZrOTf-BTC was shown to be a highly active solid Lewis acid catalyst for a broad range of important organic transformations under mild conditions, including Diels−Alder reaction, epoxide ring-opening reaction, Friedel−Crafts acylation, and alkene hydroalkoxylation reaction. The MOF catalyst outperformed Sc(OTf) 3 in terms of both catalytic activity and catalyst lifetime. Moreover, we developed a ZrOTf-BTC@SiO 2 composite as an efficient solid Lewis acid catalyst for continuous flow catalysis. The Zr centers in ZrOTf-BTC@SiO 2 feature identical coordination environment to ZrOTf-BTC based on spectroscopic evidence. ZrOTf-BTC@SiO 2 displayed exceptionally high turnover numbers (TONs) of 1700 for Diels−Alder reaction, 2700 for epoxide ring-opening reaction, and 326 for Friedel−Crafts acylation under flow conditions. We have thus created strongly Lewis acidic sites in MOFs via triflation and constructed the MOF@SiO 2 composite for continuous flow catalysis of important organic transformations.

Artificial enzymatic systems are extensively studied to mimic the structures and functions of their natural counterparts. However, there remains a significant gap between structural modeling and catalytic activity in these artificial systems. Herein we report a novel strategy for the construction of an artificial binuclear copper monooxygenase starting from a Ti metal−organic framework (MOF). The deprotonation of the hydroxide groups on the secondary building units (SBUs) of MIL-125(Ti) (MIL = Mateŕiaux de l'Institut Lavoisier) allows for the metalation of the SBUs with closely spaced Cu I pairs, which are oxidized by molecular O 2 to afford the Cu II 2 (μ 2 -OH) 2 cofactor in the MOF-based artificial binuclear monooxygenase Ti 8 -Cu 2 . An artificial mononuclear Cu monooxygenase Ti 8 -Cu 1 was also prepared for comparison. The MOF-based monooxygenases were characterized by a combination of thermogravimetric analysis, inductively coupled plasma−mass spectrometry, X-ray absorption spectroscopy, Fourier-transform infrared spectroscopy, and UV−vis spectroscopy. In the presence of coreductants, Ti 8 -Cu 2 exhibited outstanding catalytic activity toward a wide range of monooxygenation processes, including epoxidation, hydroxylation, Baeyer−Villiger oxidation, and sulfoxidation, with turnover numbers of up to 3450. Ti 8 -Cu 2 showed a turnover frequency at least 17 times higher than that of Ti 8 -Cu 1 . Density functional theory calculations revealed O 2 activation as the rate-limiting step in the monooxygenation processes. Computational studies further showed that the Cu 2 sites in Ti 8 -Cu 2 cooperatively stabilized the Cu−O 2 adduct for O−O bond cleavage with 6.6 kcal/mol smaller free energy increase than that of the mononuclear Cu sites in Ti 8 -Cu 1 , accounting for the significantly higher catalytic activity of Ti 8 -Cu 2 over Ti 8 -Cu 1 .