Metal-Organic Frameworks Integrate Cu Photosensitizers and Secondary Building Unit-Supported Fe Catalysts for Photocatalytic Hydrogen Evolution.

We report here the synthesis of a series of metal-organic frameworks (MOFs), FeX@Zr6-Cu, comprising cuprous photosensitizing linkers (Cu-PSs) and catalytically active FeII centers supported on secondary building units (SBUs) for photocatalytic H2 evolution. Close proximity (∼1 nm) between Cu-PS and SBU-supported Fe sites and stabilization of Fe sites by periodically ordered SBUs led to exceptionally high H2 evolution activity for FeX@Zr6-Cu, with turnover numbers of up to 33 700 and turnover frequencies of up to 880 h-1. Photocatalytic H2 evolution activities of FeX@Zr6-Cu correlate with the lability of X counteranions, suggesting that open coordination environments of Fe sites generated by labile X groups facilitate the formation of Fe-hydride intermediates before hydrogen evolution. This work highlights the potential of using MOFs to integrate Earth-abundant components for solar energy utilization.

Metal-Organic Frameworks Significantly Enhance Photocatalytic Hydrogen Evolution and CO2 Reduction with Earth-Abundant Copper Photosensitizers.

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.

Cerium-Based Metal-Organic Layers Catalyze Hydrogen Evolution Reaction through Dual Photoexcitation.

Cerium-based materials such as ceria are increasingly used in catalytic reactions. We report here the synthesis of the first Ce-based metal-organic layer (MOL), Ce6-BTB, comprising Ce6 secondary building units (SBUs) and 1,3,5-benzenetribenzoate (BTB) linkers, and its functionalization for photocatalytic hydrogen evolution reaction (HER). Ce6-BTB was postsynthetically modified with photosensitizing [(MBA)Ir(ppy)2]Cl or [(MBA)Ru(bpy)2]Cl2 (MBA = 2-(5'-methyl-[2,2'-bipyridin]-5-yl)acetate, ppy = 2-phenylpyridine, bpy = 2,2'-bipyridine) to afford Ce6-BTB-Ir or Ce6-BTB-Ru MOLs, respectively. The proximity of photosensitizing ligands and Ce6 SBUs in the MOLs facilitates electron transfer to drive photocatalytic HER under visible light with turnover numbers of 1357 and 484 for Ce6-BTB-Ir and Ce6-BTB-Ru, respectively. Photophysical and electrochemical studies revealed a novel dual photoexcitation pathway whereby the excited photosensitizers in the MOL are reductively quenched and then transfer electrons to Ce6 SBUs to generate CeIII centers, which are further photoexcited to CeIII* species for HER.

Metal-Organic Framework Stabilizes a Low-Coordinate Iridium Complex for Catalytic Methane Borylation.

Catalytic borylation has recently been suggested as a potential strategy to convert abundant methane to fine chemicals. However, synthetic utility of methane borylation necessitates significant improvement of catalytic activities over original phenanthroline- and diphosphine-Ir complexes. Herein, we report the use of metal-organic frameworks (MOFs) to stabilize low-coordinate Ir complexes for highly active methane borylation to afford the monoborylated product. The mono(phosphine)-Ir based MOF, Zr-P1-Ir, significantly outperformed other Ir catalysts in methane borylation to afford CH3Bpin with a turnover number of 127 at 110 °C. Density functional theory calculations indicated a significant reduction of activation barrier for the rate limiting oxidative addition of methane to the four-coordinate (P1)IrIII(Bpin)3 catalyst to form the six-coordinate (P1)IrV(Bpin)3(CH3)(H) intermediate, thus avoiding the formation of sterically encumbered seven-coordinate IrV intermediates as found in other Ir catalysts based on chelating phenanthroline, bipyridine, and diphosphine ligands. MOF thus stabilizes the homogeneously inaccessible, low-coordinate (P1)Ir(boryl)3 catalyst to provide a unique strategy to significantly lower the activation barrier for methane borylation. This MOF-based catalyst design holds promise in addressing challenging catalytic reactions involving highly inert substrates.

An in Situ Embedded Square-Planar CuII/NiIIN4 Metalloligand in Coordination Polymers for Visible-Light Photocatalysis.

Three coordination polymers (CPs) with square-planar CuII/NiIIN4 subunits were formed in one step by subcomponent self-assembly, giving rise to an unprecedented linking variety of in situ embedded metalloligands and CuI clusters. All CPs exhibit unusual visible-light adsorption. Enhanced photocatalytic activity and high selectivity were observed in the oxidation of benzene under visible-light irradiation.

Tether-directed bisfunctionalization reactions of c60 and c70.

Four easily isolable regio- and stereoselective bis-adducts of C60 and C70 , as well as a new C70 -dumbbell derivative, have been synthesized by using two different bismalonate tethered moieties. The derivatives that possess relatively long-tethered moieties show highly symmetric addition patterns, as evidenced by spectroscopic measurements, whereas the derivatives possessing the shorter-tethered moiety exhibit interesting addition patterns on C60 and C70 .

An in situ derived MOF@In2S3 heterojunction stabilizes Co(II)-salicylaldimine for efficient photocatalytic formic acid dehydrogenation.

We report here the hierarchical construction of a molecular Co(II)-salicylaldimine catalyst and an in situ derived In2S3 semiconductor in a MOF@In2S3 heterojunction through sequentially controllable in situ etching and post-synthetic modification for photocatalytic hydrogen production from formic acid. The enhanced catalyst stability and facilitated charge carrier mobility between the In2S3 photosensitizers and Co catalyst realize a superior H2 production rate of 18 746 µmol g-1 h-1 (selectivity > 99.9%) with a turnover number (TON) of up to 6146 in 24 h (apparent quantum efficiency of 3.8% at 420 nm), indicating a 165-fold enhancement over that of the pristine MOF. This work highlights a powerful strategy for synergistic Earth-abundant metal-based MOF photocatalysis in promoting H2 production from FA.

Amorphous TiO2@NH2-MIL-125(Ti) homologous MOF-encapsulated heterostructures with enhanced photocatalytic activity.

We have provided the first case of successfully synthesising amorphous TiO2@NH2-MIL-125(Ti) MOF-encapsulated heterostructures by a facile process. The homologous heterostructures exhibited higher photocatalytic activity via efficient transfer of photoinduced carriers as well as preservation of trivalent titanium ions.