CO2 capture and electrochemical conversion is a sustainable and circular process to produce carbon‐based chemicals. Capture of CO2 can be achieved with amine‐based capturing agents, which have been reported in combination with homogeneous catalysts in solution. Amines have a range of effects on CO2 reduction catalysis, depending on how they bind CO2, interact with the electrolyte, and with the catalyst, among other effects. The homogeneous complex Mn(bpy)(CO)3Br is a well‐studied catalyst that can selectively produce carbon monoxide (CO) or formate (HCOO–), depending on the conditions. It has been demonstrated that the presence of amines can promote the selective formation of formic acid. In this work, Mn(bpy)(CO)3Br was immobilized on an electrode via supramolecular interactions. The resulting material was studied in electrochemical CO2 reduction under aqueous conditions with and without triethanolamine (TEOA) present as a CO2 capturing agent. We demonstrated that the presence of TEOA causes two effects: (1) a two‐fold increased catalytic activity in TON and (2) an increased selectivity for formate, from 36% to 60% Faraday efficiency. It showed that TEOA is an excellent additive for such catalytic systems and demonstrated the potential of expanding such catalytic systems to achieve more active and selective for aqueous CO2 reduction.

Metal-organic frameworks (MOFs) containing photoactive organic linkers are promising platforms for artificial photosynthesis, yet the nature of the photoactive state in Zr(IV)-based MOFs remains controversial, particularly the proposed involvement of transient Zr(III) centers formed through linker-to-node charge transfer. Here, we elucidate the mechanism of CO 2 -to-formate conversion in MOFs by comparing redox-active PCN-223 with redox-inactive UiO-66-NH 2 . Although both MOFs contain the same Zr 6 -oxo cluster, their linkers differ in redox activity and interchromophore coupling, which allowed us to decouple linker-driven excited-state interactions from cluster-centered contributions to photocatalysis. Using in situ X-ray absorption spectroscopy, electron paramagnetic resonance, infrared spectroscopy, and transient optical spectroscopy, we show that the Zr 6 -oxo cluster remains redox-inactive during photocatalysis, ruling out linker-to-node electron transfer as the dominant pathway. Instead, framework assembly in PCN-223 induces strong interporphyrin coupling that promotes exciton delocalization and symmetry-breaking charge separation, generating long-lived linker-centered radical states absent in molecular porphyrins. Triethanolamine selectively scavenges the oxidized porphyrin species, stabilizing the reduced radical and enabling accumulation of photogenerated reducing equivalents within the framework. Remarkably, CO 2 reduction proceeds even after illumination ceases, revealing photocharging behavior in which stored linker-centered charges sustain catalysis in the dark. We further provide direct evidence for transient CO 2 •− species, which is consistent with a proton-coupled electron-transfer pathway inside the MOF pores. Together, these findings show that collective chromophore interactions, rather than metal-node redox chemistry, govern charge separation, charge storage, and catalytic reactivity in photoactive Zr-MOFs.

Herein, a selective, one‐pot synthetic route to reactive benzyl‐ and allyl‐halide‐substituted naphthalenes and dihydronaphthalenes from easily accessible 2,3‐aryl‐1,3‐butadiene substrates and simple halogenated alkanes, using [Cp*RuCl(PPh 3 ) 2 ] as the catalyst, is reported. The reaction is tolerant to various functional groups, including reactive carbonyl groups, halides, and trimethylsilyl groups. The scope of catalytic reactions can be expanded to otherwise difficult to synthesize substituted and reactive dihydronaphthalene and benzo[ b ]thiophene products. The resulting benzyl‐ and allyl‐halide‐substituted (dihydro‐)naphthalene products are relevant synthons for drug synthesis, allowing for facile post‐functionalization by making use of the reactive halide functionalities. Mechanistic studies are combined with density functional theory (DFT), which revealed a sequential catalytic atom transfer radical addition, radical benzannulation, and HCl elimination sequence. It is particularly noteworthy that the key transition state proceeds via a 6‐ endo‐trig cyclization, in contrast to the classical 5‐ exo ‐trig cyclization as is normally observed for intramolecular radical additions. This cyclized intermediate subsequently undergoes HCl elimination to generate benzyl‐ and allyl‐halide substituted (dihydro‐)naphthalenes.

We report a unique one-pot synthetic route to reactive benzyl- and allyl-halide-substituted naphthalenes and dihydronaphthalenes from 2,3-aryl-1,3-butadiene substrates and halogenated alkanes with [Cp*RuCl(PPh3)2], a commercially available catalyst. The reaction is tolerant to various functional groups, including reactive carbonyl groups, halides, and trimethylsilyl groups. The scope of catalytic reactions was expanded to include a heteroaromatic thiophene ring system, demonstrating full regioselectivity toward the benzo[b]thiophene product. The resulting (dihydro-)naphthalene products are relevant synthons for drug synthesis, allowing for facile post-functionalization by making use of the reactive (benzylic or allylic) halide functionalities. Mechanistic studies were combined with DFT, which revealed a sequential catalytic ATRA, radical benzannulation, and HCl elimination sequence. The initial ATRA step results in a 1,4-addition intermediate that subsequently undergoes a 6-endo-trig cyclization via a radical addition on the pendant arene. This cyclized intermediate subsequently undergoes HCl elimination to generate benzyl- and allyl-halide substituted (dihydro-)naphthalenes.

Selective CO2 reduction to formate is challenging due to similar thermodynamics for reaction to other products such carbon monoxide and molecular hydrogen. Formate production can be achieved via hydride transfer from metal-hydride complexes or organic catalysts; the latter being inspired by structure and activity of the NADH co-factor in natural photosynthesis. Most known synthetic NADH mimics can selectively produce formate, yet they suffer from sluggish kinetics, which is limiting their applicability. In a combined experimental and theoretical study, we demonstrate that naphthalene monoamide Meisenheimer complex NMI(H)- is a strong organic hydride donor with the ability to reduce CO2 to formate. DFT calculations are used to benchmark the thermodynamic hydricity of NMI(H)- in comparison with previously known NADH mimics.

Atom transfer radical addition (ATRA) of halogenated compounds with alkenes is well established but primary alkyl chlorides are understudied because of the difficult C-Cl bond activation. In this paper, we show that TONs of 61 can be achieved in the ATRA of ethyl chloroacetate onto styrene with [Cp*Ru(Cl)(2)(PPh3)] and 1,1'-azobis(cyclohexanecarbonitrile) (ACHN) as a radical initiator, representing a three-fold improvement compared to previous reports. New catalyst precursors of the type [Cp*Ru(Cl)(2)(PR3)] were synthesized and tested (R=Me, Et, Cy, Ph, p-CF3C6H4 and p-MeOC6H4). The kinetic reaction profiles were studied using in situ ATR-FTIR spectroscopy. Among these complexes, [Cp*Ru(Cl)(2)(PPh3)] gave the best yields while [Cp*Ru(Cl)(2)(PMe3)] showed the highest rate. While rates correlate with redox potentials (electronics), our investigation reveals that substrate sterics are important for the overall yield. Density functional theory calculations suggest an open-shell singlet pathway, where polymerization is kinetically disfavored, explaining the selectivity towards ATRA products.

Free-base porphyrins can be protonated, which significantly impacts their electronic and excited state properties. While excited state dynamics are well explored for either neutral or fully protonated porphyrins, the intermediate region has not yet been explored, although their potential implications for photocatalytic reactions are evident. This study explores how partial protonation affects the nature and properties of photoexcited states of tetrakis(4-carboxyphenyl)porphyrin (TCPP) using steady-state and nanosecond transient absorption spectroscopy. Global-fit analysis of the decay curves revealed the formation of a protonated excited triplet state from the neutral triplet state, as well as the long lifetimes of these species of up to 120 mu s. The photoexcited triplet state of TCPP functions as a photobase, which was confirmed by computational analysis of the electron density of the exited states showing increased nucleophilicity at the unprotonated nitrogen atoms of the porphyrin core. These findings indicate that photoinduced protonated excited triplet states can function as electron acceptors with anodically shifted redox potentials, opening new pathways for porphyrin-based photoreactions. Partial protonation of free-base porphyrins impacts their excited states, with implications for photocatalysis, studied via steady-state and nanosecond spectroscopy.

Photoredox catalysis is a valuable tool in a large variety of chemical reactions. Main challenges still to be overcome are photodegradation of photocatalysts and substrates, short lifetimes of reactive intermediates, and selectivity issues due to unwanted side reactions. A potential solution to these challenges is the pre-organization of the photosensitizer, substrate and (co)-catalyst in supramolecular self-assembled structures. In such architectures, (organic) dyes can be stabilized, and higher selectivity could potentially be achieved through pre-organizing desired reaction partners via non-covalent interactions. Perylene diimide (PDI) is an organic dye, which can be readily reduced to its mono- and dianion. Excitation of both anions leads to highly reducing excited states, which are able to reduce a variety of substrates via single electron transfer. The incorporation of PDI into a heteroleptic [M4La2Lb2] supramolecular square has been recently demonstrated. Herein we investigate its photophysical properties and demonstrate that incorporated PDI indeed features photocatalytic activity. Initial results suggest that the pre-organisation by binding positively affects the outcome.

In Chemistry - A European Journal, N AE sborg and co-workers have demonstrated a simple protocol that overcomes oxygen sensitivity in triplet-sensitized [2 + 2] photocycloaddition. A sodium dodecyl sulfate (SDS)-based micelle is used to trap oxygen within the core while photosenstizer [Ru(bpy)3]2+ and the substrate are pre-orga-nized within the Stern layer. Unwanted quenching of the triplet excited photosensitizer is thereby prevented.

Because sunlight is the most abundant energy source on earth, it has huge potential for practical applications ranging from sustainable energy supply to light driven chemistry. From a chemical perspective, excited states generated by light make thermodynamically uphill reactions possible, which forms the basis for energy storage into fuels. In addition, with light, open-shell species can be generated which open up new reaction pathways in organic synthesis. Crucial are photosensitizers, which absorb light and transfer energy to substrates by various mechanisms, processes that highly depend on the distance between the molecules involved. Supramolecular coordination cages are well studied and synthetically accessible reaction vessels with single cavities for guest binding, ensuring close proximity of different components. Due to high modularity of their size, shape, and the nature of metal centers and ligands, cages are ideal platforms to exploit preorganization in photocatalysis. Herein we focus on the application of supramolecular cages for photocatalysis in artificial photosynthesis and in organic photo(redox) catalysis. Finally, a brief overview of immobilization strategies for supramolecular cages provides tools for implementing cages into devices. This review provides inspiration for future design of photocatalytic supramolecular host-guest systems and their application in producing solar fuels and complex organic molecules.

Eva Meeus opened discussion of the paper by Helma Wennemers: I was wondering whether you could "revert" this process? More specifically, can you equip your peptide-based template to enable length-controlled scissions of oligomers to facilitate, for example, monomer recycling? Helma Wennemers answered: Yes, this i

Transition metal catalysis is of utmost importance for the development of sustainable processes in academia and industry. The activity and selectivity of metal complexes are typically the result of the interplay between ligand and metal properties. As the ligand can be chemically altered, a large research focus has been on ligand development. More recently, it has been recognized that further control over activity and selectivity can be achieved by using the "second coordination sphere", which can be seen as the region beyond the direct coordination sphere of the metal center. Hydrogen bonds appear to be very useful interactions in this context as they typically have sufficient strength and directionality to exert control of the second coordination sphere, yet hydrogen bonds are typically very dynamic, allowing fast turnover. In this review we have highlighted several key features of hydrogen bonding interactions and have summarized the use of hydrogen bonding to program the second coordination sphere. Such control can be achieved by bridging two ligands that are coordinated to a metal center to effectively lead to supramolecular bidentate ligands. In addition, hydrogen bonding can be used to preorganize a substrate that is coordinated to the metal center. Both strategies lead to catalysts with superior properties in a variety of metal catalyzed transformations, including (asymmetric) hydrogenation, hydroformylation, C-H activation, oxidation, radical-type transformations, and photochemical reactions.

Progress in metallo-supramolecular chemistry creates potential to synthesize functional nano systems and intelligent materials of increasing complexity. In the past four decades, metal-mediated self-assembly has produced a wide range of structural motifs such as helicates, grids, links, knots, spheres and cages, with particularly the latter ones catching growing attention, owing to their nano-scale cavities. Assemblies serving as hosts allow application as selective receptors, confined reaction environments and more. Recently, the field has made big steps forward by implementing dedicated functionality, e.g. catalytic centres or photoswitches to allow stimuli control. Besides incorporation in homoleptic systems, composed of one type of ligand, desire arose to include more than one function within the same assembly. Inspiration comes from natural enzymes that congregate, for example, a substrate recognition site, an allosteric regulator element and a reaction centre. Combining several functionalities without creating statistical mixtures, however, requires a toolbox of sophisticated assembly strategies. This review showcases the implementation of function into self-assembled cages and devises strategies to selectively form heteroleptic structures. We discuss first examples resulting from a combination of both principles, namely multicomponent multifunctional host-guest complexes, and their potential in application in areas such as sensing, catalysis, and photo-redox systems.

Metal–organic frameworks (MOFs) and supramolecular coordination cages (SCCs) have generated increasing interest for catalysis applications. In this chapter, we discuss design strategies for functional MOFs and SCCs. How can catalysts be introduced? What kind of catalysis can be performed with these materials? What are the main differences and similarities between MOFs and discrete SCCs, and what can these fields learn from each other?

The conversion of the 1 : 1-complex of Cisplatin with 1-methyluracil (1MeUH), cis-[Pt(NH3 )2 (1MeU-N3)Cl] (1 a) to the aqua species cis-[Pt(NH3 )2 (1MeU-N3)(OH2 )]+ (1 b), achieved by reaction of 1 a with AgNO3 in water, affords a mixture of compounds, the composition of which strongly depends on sample history. The complexity stems from variations in condensation patterns and partial loss of NH3 ligands. In dilute aqueous solution, 1 a, and dinuclear compounds cis-[(NH3 )2 (1MeU-N3)Pt(μ-OH)Pt(1MeU-N3)(NH3 )2 ]+ (3) as well as head-tail cis-[Pt2 (NH3 )4 (μ-1MeU-N3,O4)2 ]2+ (4) represent the major components. In addition, there are numerous other species present in minor quantities, which differ in metal nuclearity, stoichiometry, stereoisomerism, and Pt oxidation state, as revealed by a combination of 1 H NMR and ESI-MS spectroscopy. Their composition appears not to be the consequence of a unique and repeating coordination pattern of the 1MeU ligand in oligomers but rather the coexistence of distinctly different condensation patterns, which include μ-OH, μ-1MeU, and μ-NH2 bridging and combinations thereof. Consequently, the products obtained should, in total, be defined as a heterogeneous mixture rather than a mixture of oligomers of different sizes. In addition, a N2 complex, [Pt(NH3 )(1MeU)(N2 )]+ appears to be formed in gas phase during the ESI-MS experiment. In the presence of Na+ ions, multimers n of 1 a with n=2, 3, 4 are formed that represent analogues of non-metalated uracil quartets found in tetrastranded RNA.

Photochemical hydrogen evolution from a UiO-66-incorporated Fe-2(dcbdt)(CO)(6) catalyst in conjunction with a ruthenium photosensitizer and an ascorbate donor ceases after a period of irradiation, but is restored after a 60 min. resting period in the dark. Control experiments show that neither product inhibition nor pore clogging is responsible for this surprising behaviour, and intra-crystal linker scrambling is proposed as a potential explanation.

An acridone-based, interpenetrated double cage [3BF4Pd4L8] acts as a photosensitizer for generating singlet oxygen which adds to 1,3-cyclohexadiene in a [2+4] hetero-Diels-Alder reaction to form 2,3-dioxabicyclo[2.2.2]oct-5-ene. Photocatalytic activity was exclusively observed for the assembled cage, whereas the free organic ligand L decomposes upon irradiation. While cage [3BF4Pd4L8] does not accept any organic guests, NMR, MS and single crystal X-ray results reveal that both substrate and product are readily encapsulated in the central pocket of its chloride-activated form [2Cl@Pd4L8]. The system combines multiple functions (photosensitization, allosteric activation and guest uptake) within a structurally complex, mechanically-bound self-assembly built up from a simple and readily accessible ligand.

Correction for ‘Substrate and product binding inside a stimuli-responsive coordination cage acting as a singlet oxygen photosensitizer’ by Sonja Pullen et al., Dalton Trans., 2020, 49, 9404–9410, DOI: 10.1039/D0DT01674H.

ConspectusPorous nanostructures and materials based on metal-mediated self-assembly have developed into a vibrantly studied subdiscipline of supramolecular chemistry during the past decades. In principle, two branches of such coordination compounds can be distinguished: Metal–organic frameworks (MOFs) on the one side represent infinite porous networks of metals or metal clusters that are connected via organic ligands to give solid-state materials. On the other hand, metal–organic cages (MOCs) are discrete and soluble systems with only a limited number of pores. Formation of a particular structure type is achieved by carefully balancing the donor site angles within the ligands as well as the nature and coordination geometry of the metal component. Years of research on MOFs and MOCs has yielded numerous types of well-defined porous crystals and complex supramolecular architectures. Since various synthetic routes and postsynthetic modification methods have been established, the focus of recent developments has moved toward the preparation of multifunctional systems that are able to mimic the structural and functional complexity of natural enzymes.This Account compares different strategies to prepare multifunctional MOFs and heteroleptic MOCs and gives a perspective on where to move forward. While the preparative toolbox for multifunctional MOFs is already quite mature, pore accessibility and substrate diffusion within the crystal have been identified as major challenges yet to be overcome. Only recently have a set of different strategies for the assembly of heteroleptic MOCs been developed. Such multifunctional cages can be formed from either partially protected or "naked" metal cations. Controlled assembly, producing single products rather than statistical mixtures, leans on assembly-dependent approaches making use of either steric effects or shape complementarity between the ligands. Further strategies include coordination-site engineering and hierarchical assembly of preformed components. The main challenge with heteroleptic, functional MOCs is to find a balance between the required dynamic assembly fidelity and the stability of the resulting system under operating conditions. If these limitations can be overcome in the future, chemists will be able to design multifunctional systems of similar activity and complexity as nature's enzymes from simple and easily accessible synthetic building blocks. Major impacts on chemical sensing, small-molecule recognition and sequestration, drug delivery, and catalysis will be achieved by these materials.