Site-Isolated Rhodium(II) Metalloradicals Catalyze Olefin Hydrofunctionalization

Rh(II) porphyrin complexes display pronounced metal-centered radical character and the ability to activate small molecules under mild conditions, but catalysis with Rh(II) porphyrins is extremely rare. In addition to facile dimerization, Rh(II) porphyrins readily engage in kinetically and thermodynamically facile reactions involving two Rh(II) centers to generate stable Rh(III)-X intermediates that obstruct turnover in thermal catalysis. Here we report site isolation of Rh(II) metalloradicals in a MOF host, which not only protects Rh(II) metalloradicals against dimerization, but also allows them to participate in thermal catalysis. Access to PCN-224 or PCN-222 in which the porphyrin linkers are fully metalated by Rh(II) in the absence of any accompanying Rh(0) nanoparticles was achieved via the first direct MOF synthesis with a linker containing a transition-metal alkyl moiety, followed by Rh(III)-C bond photolysis.

Understanding and Controlling Molecular Compositions and Properties in Mixed-Linker Porphyrin Metal-Organic Frameworks

Porphyrin-based metal-organic frameworks (MOFs) are attractive materials for photo- and thermally activated catalysis due to their unique structural features related to the porphyrin moiety, guest-accessible porosity, and high chemical tunability. In this study, we report the synthetic incorporation of nonplanar β-ethyl-functionalized porphyrin linkers into the framework structure of PCN-222, obtaining a solid-solution series of materials with different modified linker contents. Comprehensive analysis by a combination of characterization techniques, such as NMR, UV-vis and IR spectroscopy, powder X-ray diffraction, and N2 sorption analysis, allows for the confirmation of linker incorporation. A detailed structural analysis of intrinsic material properties, such as the thermal response of the different materials, underlines the complexity of synthesizing and understanding such materials. This study presents a blueprint for synthesizing and analyzing porphyrin-based mixed-linker MOF systems and highlights the hurdles of characterizing such materials.

Recent Synthetic Advances on the Use of Diazo Compounds Catalyzed by Metalloporphyrins

Diazo compounds are organic substances that are often used as precursors in organic synthesis like cyclization reactions, olefinations, cyclopropanations, cyclopropenations, rearrangements, and carbene or metallocarbene insertions into C-H, N-H, O-H, S-H, and Si-H bonds. Typically, reactions from diazo compounds are catalyzed by transition metals with various ligands that modulate the capacity and selectivity of the catalyst. These ligands can modify and enhance chemoselectivity in the substrate, regioselectivity and enantioselectivity by reflecting these preferences in the products. Porphyrins have been used as catalysts in several important reactions for organic synthesis and also in several medicinal applications. In the chemistry of diazo compounds, porphyrins are very efficient as catalysts when complexed with low-cost metals (e.g., Fe and Co) and, therefore, in recent years, this has been the subject of significant research. This review will summarize the advances in the studies involving the field of diazo compounds catalyzed by metalloporphyrins (M-Porph, M = Fe, Ru, Os, Co, Rh, Ir) in the last five years to provide a clear overview and possible opportunities for future applications. Also, at the end of this review, the properties of artificial metalloenzymes and hemoproteins as biocatalysts for a broad range of applications, namely those concerning carbene-transfer reactions, will be considered.

Metal organic frameworks derived functional materials for energy and environment related sustainable applications

With the vigorous development of industrial economy, energy and environmental problems have become the most serious issues affecting people's production and life. Therefore, the demand for clean energy production, effective separation and storage is growing. Metal-organic frameworks (MOFs), as a kind of porous crystalline materials with large surface area and porosity, which is self-assembled by metal ions or clusters and organic ligands through coordination bonds. Thanks to a number of unique characteristics such as adjustable pore environment, homogeneous void structure, abundant active sites, unprecedented chemical composition tunability and functional versatility, it has been widely studied, especially for the clean energy conversion in catalysis. In this review, we focus on the research progress of clean energy in catalysis based on MOFs. Emphasis is placed on MOFs with different structures of compositions and their applications in catalytic for clean energy conversion, such as CO oxidation, CO₂ reduction and H₂ evolution. In addition, the situation of MOFs assisting environmental remediation is also briefly described. Finally, the prospects and challenges of MOFs in clean energy and the remaining issues in this field are presented.

MOF-enabled confinement and related effects for chemical catalyst presentation and utilization

A defining characteristic of nearly all catalytically functional MOFs is uniform, molecular-scale porosity. MOF pores, linkers and nodes that define them, help regulate reactant and product transport, catalyst siting, catalyst accessibility, catalyst stability, catalyst activity, co-catalyst proximity, composition of the chemical environment at and beyond the catalytic active site, chemical intermediate and transition-state conformations, thermodynamic affinity of molecular guests for MOF interior sites, framework charge and density of charge-compensating ions, pore hydrophobicity/hydrophilicity, pore and channel rigidity vs. flexibility, and other features and properties. Collectively and individually, these properties help define overall catalyst functional behaviour. This review focuses on how porous, catalyst-containing MOFs capitalize on molecular-scale confinement, containment, isolation, environment modulation, energy delivery, and mobility to accomplish desired chemical transformations with potentially superior selectivity or other efficacy, especially in comparison to catalysts in homogeneous solution environments.

Topology- and wavelength-governed CO2 reduction photocatalysis in molecular catalyst-metal–organic framework assemblies

Optimising catalyst materials for visible light-driven fuel production requires understanding complex and intertwined processes including light absorption and catalyst stability, as well as mass, charge, and energy transport. These phenomena can be uniquely combined (and ideally controlled) in porous host–guest systems. Towards this goal we designed model systems consisting of molecular complexes as catalysts and porphyrin metal–organic frameworks (MOFs) as light-harvesting and hosting porous matrices. Two MOF-rhenium molecule hybrids with identical building units but differing topologies (PCN-222 and PCN-224) were prepared including photosensitiser-catalyst dyad-like systems integrated via self-assembled molecular recognition. This allowed us to investigate the impact of MOF topology on solar fuel production, with PCN-222 assemblies yielding a 9-fold turnover number enhancement for solar CO₂-to-CO reduction over PCN-224 hybrids as well as a 10-fold increase compared to the homogeneous catalyst-porphyrin dyad. Catalytic, spectroscopic and computational investigations identified larger pores and efficient exciton hopping as performance boosters, and further unveiled a MOF-specific, wavelength-dependent catalytic behaviour. Accordingly, CO₂ reduction product selectivity is governed by selective activation of two independent, circumscribed or delocalised, energy/electron transfer channels from the porphyrin excited state to either formate-producing MOF nodes or the CO-producing molecular catalysts.

Two MOF molecular catalyst hybrids with differing topologies show mass and light transport governed photocatalysis. MOF-specific, irradiation wavelength-dependent product control is unlocked by switching between two energy/electron transfer channels.

Metal-organic frameworks as catalytic selectivity regulators for organic transformations

Selective organic transformations using metal-organic frameworks (MOFs) and MOF-based heterogeneous catalysts have been an intriguing but challenging research topic in both the chemistry and materials communities. Analogous to the reaction specificity achieved in enzyme pockets, MOFs are also powerful platforms for regulating the catalytic selectivity via engineering their catalytic microenvironments, such as metal node alternation, ligand functionalization, pore decoration, topology variation and others. In this review, we provide a comprehensive introduction and discussion about the role of MOFs played in regulating and even boosting the size-, shape-, chemo-, regio- and more appealing stereo-selectivity in organic transformations. We hope that it will be instructive for researchers in this field to rationally design, conveniently prepare and elaborately functionalize MOFs or MOF-based composites for the synthesis of high value-added organic chemicals with significantly improved selectivity.

Defect Engineering of Copper Paddlewheel-Based Metal-Organic Frameworks of Type NOTT-100: Implementing Truncated Linkers and Its Effect on Catalytic Properties

A series of new defect-engineered metal-organic frameworks (DEMOFs) were synthesized by framework doping with truncated linkers employing the mixed-linker approach. Two tritopic defective (truncated) linkers, biphenyl-3,3',5-tricarboxylates (L_H) lacking a ligating group and 5-(5-carboxypyridin-3-yl)isophthalates (L_Py) bearing a weaker interacting ligator site, were integrated into the framework of Cu₂(BPTC) (NOTT-100, BPTC = biphenyl-3,3',5,5'-tetracarboxylates). Incorporating L_H into the framework mainly generates missing metal node defects, thereby obtaining dangling COOH groups in the framework. However, introducing L_Py forms more modified metal nodes featuring reduced and more accessible Cu sites. In comparison with the pristine NOTT-100, the defect-engineered NOTT-100 (DE-NOTT-100) samples show two unique features: (i) functional groups (the protonated carboxylate groups as the Brønsted acid sites or the pyridyl N atoms as the Lewis basic sites), which can act as second active sites, are incorporated into the MOF frameworks, and (ii) more modified paddlewheels, which provided extra coordinatively unsaturated sites, are generated. The cooperative functioning of the above characteristics enhances the catalytic performance of certain types of reactions. For a proof of concept, two exemplary reactions, namely, the cycloaddition of CO₂ with propylene oxide to propylene carbonate and the cyclopropanation of styrene, were carried out to evaluate the catalytic activities of those DE-NOTT-100 materials depending on the defect structure.

Thermal defect engineering of precious group metal–organic frameworks: impact on the catalytic cyclopropanation reaction

This work highlights the catalytic cyclopropanation and its characteristics as a novel analytical tool to investigate complex MOF structures.