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The development of artificial biomimetic systems with real-world applications relies on a profound understanding of all photophysical and photochemical processes taking place upon light absorption by a chromophoric unit. Efficient photoinduced charge separation in photosensitizers or specialized photocatalysts is the process triggering most of the chemical reactions in the production of solar fuels, and hence, its proper characterization is of utmost importance. In this work, we investigated photoinduced charge separation processes in a perfluorinated Zn-tetraphenylporphyrin photosensitizer (ZnF20). Ascorbate and 1,4-diazabicyclo[2.2.2]octane (DABCO) were used as reversible electron donors for nanosecond-resolved pump–probe experiments using both optical absorption and resonance Raman scattering as probes. Our results indicate that in spite of similar charge separation efficiencies, the DABCO-containing system exhibits a much faster kinetics of charge-separated state formation and decay. This is attributed to its inherent ability to coordinate to the metal center. Time-resolved resonance Raman measurements allow for the detection of vibrational modes specific to both the triplet excited state of ZnF20 and its reduced state, complementing transient absorption data to fully characterize the charge separation process. [ABSTRACT FROM AUTHOR]

A close mimic of P680 and the TyrosineZ‐Histidine190 pair in photosystem II (PS II) has been synthesized using a ruthenium chromophore and imidazole‐phenol ligands. The intramolecular oxidation of the ligands by the photoproduced Ru(III) species is characterized by a small driving force, very similar to PS II where the complexity of kinetics was attributed to the reversibility of electron transfer steps. Laser flash photolysis revealed biphasic kinetics for ligand oxidation. The fast phase (τ<50 ns) corresponds to partial oxidation of the imidazole‐phenol ligand, proton transfer within the hydrogen bond, and formation of a neutral phenoxyl radical. The slow phase (5–9 μs) corresponds to full oxidation of the ligand which is kinetically controlled by deprotonation of the distant 1‐nitrogen of the imidazolium. These results show that imidazole with its two protonatable sites plays a special role as a proton relay in a 'proton domino' reaction. [ABSTRACT FROM AUTHOR]

Iron porphyrins are among the most studied molecular catalysts for carbon dioxide (CO2) reduction and their reactivity is constantly being enhanced through the implementation of chemical functionalities in the second coordination sphere inspired by the active sites of enzymes. In this study, we were intrigued to observe that a multipoint hydrogen bonding scheme provided by embarked urea groups could also shift the redox activation step of CO2 from the well‐admitted Fe(0) to the Fe(I) state. Using EPR, resonance Raman, IR and UV‐Visible spectroscopies, we underpinned a two‐electron activation step of CO2 starting from the Fe(I) oxidation state to form, after protonation, an Fe(III)−COOH species. The addition of another electron and a proton to the latter species converged to the cleavage of a C−O bond with the loss of water molecule resulting in an Fe(II)−CO species. DFT analyses of these postulated intermediates are in good agreement with our collected spectroscopic data, allowing us to propose an alternative pathway in the catalytic CO2 reduction with iron porphyrin catalyst. Such a remarkable shift opens new lines of research in the design of molecular catalysts to reach low overpotentials in performing multi‐electronic CO2 reduction catalysis. [ABSTRACT FROM AUTHOR]

Iron porphyrins are among the most studied molecular catalysts for carbon dioxide (CO2) reduction and their reactivity is constantly being enhanced through the implementation of chemical functionalities in the second coordination sphere inspired by the active sites of enzymes. In this study, we were intrigued to observe that a multipoint hydrogen bonding scheme provided by embarked urea groups could also shift the redox activation step of CO2 from the well‐admitted Fe(0) to the Fe(I) state. Using EPR, resonance Raman, IR and UV‐Visible spectroscopies, we underpinned a two‐electron activation step of CO2 starting from the Fe(I) oxidation state to form, after protonation, an Fe(III)−COOH species. The addition of another electron and a proton to the latter species converged to the cleavage of a C−O bond with the loss of water molecule resulting in an Fe(II)−CO species. DFT analyses of these postulated intermediates are in good agreement with our collected spectroscopic data, allowing us to propose an alternative pathway in the catalytic CO2 reduction with iron porphyrin catalyst. Such a remarkable shift opens new lines of research in the design of molecular catalysts to reach low overpotentials in performing multi‐electronic CO2 reduction catalysis. [ABSTRACT FROM AUTHOR]

The core challenge in developing cost‐efficient catalysts for carbon dioxide (CO2) conversion mainly lies in controlling its complex reaction pathways. One such strategy exploits bimetallic cooperativity, which relies on the synergistic interaction between two metal centers to activate and convert the CO2 substrate. While this approach has seen an important trend in heterogeneous catalysis as a handle to control stabilities of surface intermediates, it has not often been utilized in molecular and heterogenized molecular catalytic systems. In this review, we gather general principles on how natural CO2 activating enzymes take advantage of bimetallic strategy and how phosphines, cyclams, polypyridyls, porphyrins, and cryptates‐based homo‐ and hetero‐bimetallic molecular catalysts can help understand the synergistic effect of two metal centers. [ABSTRACT FROM AUTHOR]

At the core of carbon monoxide dehydrogenase (CODH) active site two metal ions together with hydrogen bonding scheme from amino acids orchestrate the interconversion between CO2 and CO. We have designed a molecular catalyst implementing a bimetallic iron complex with an embarked second coordination sphere with multi‐point hydrogen‐bonding interactions. We found that, when immobilized on carbon paper electrode, the dinuclear catalyst enhances up to four fold the heterogeneous CO2 reduction to CO in water with an improved selectivity and stability compared to the mononuclear analogue. Interestingly, quasi‐identical catalytic performances are obtained when one of the two iron centers was replaced by a redox inactive Zn metal, questioning the cooperative action of the two metals. Snapshots of X‐ray structures indicate that the two metalloporphyrin units tethered by a urea group is a good compromise between rigidity and flexibility to accommodate CO2 capture, activation, and reduction. [ABSTRACT FROM AUTHOR]

At the core of carbon monoxide dehydrogenase (CODH) active site two metal ions together with hydrogen bonding scheme from amino acids orchestrate the interconversion between CO2 and CO. We have designed a molecular catalyst implementing a bimetallic iron complex with an embarked second coordination sphere with multi‐point hydrogen‐bonding interactions. We found that, when immobilized on carbon paper electrode, the dinuclear catalyst enhances up to four fold the heterogeneous CO2 reduction to CO in water with an improved selectivity and stability compared to the mononuclear analogue. Interestingly, quasi‐identical catalytic performances are obtained when one of the two iron centers was replaced by a redox inactive Zn metal, questioning the cooperative action of the two metals. Snapshots of X‐ray structures indicate that the two metalloporphyrin units tethered by a urea group is a good compromise between rigidity and flexibility to accommodate CO2 capture, activation, and reduction. [ABSTRACT FROM AUTHOR]

Iron porphyrins are among the best molecular catalysts for the electrocatalytic CO2 reduction reaction. Powering these catalysts with the help of photosensitizers comes along with a couple of unsolved challenges that need to be addressed with much vigor. We have designed an iron porphyrin catalyst decorated with urea functions (UrFe) acting as a multipoint hydrogen bonding scaffold towards the CO2 substrate. We found a spectacular photocatalytic activity reaching unreported TONs and TOFs as high as 7270 and 3720 h−1, respectively. While the Fe0 redox state has been widely accepted as the catalytically active species, we show here that the FeI species is already involved in the CO2 activation, which represents the rate‐determining step in the photocatalytic cycle. The urea functions help to dock the CO2 upon photocatalysis. DFT calculations bring support to our experimental findings that constitute a new paradigm in the catalytic reduction of CO2. [ABSTRACT FROM AUTHOR]

Iron porphyrins are among the best molecular catalysts for the electrocatalytic CO2 reduction reaction. Powering these catalysts with the help of photosensitizers comes along with a couple of unsolved challenges that need to be addressed with much vigor. We have designed an iron porphyrin catalyst decorated with urea functions (UrFe) acting as a multipoint hydrogen bonding scaffold towards the CO2 substrate. We found a spectacular photocatalytic activity reaching unreported TONs and TOFs as high as 7270 and 3720 h−1, respectively. While the Fe0 redox state has been widely accepted as the catalytically active species, we show here that the FeI species is already involved in the CO2 activation, which represents the rate‐determining step in the photocatalytic cycle. The urea functions help to dock the CO2 upon photocatalysis. DFT calculations bring support to our experimental findings that constitute a new paradigm in the catalytic reduction of CO2. [ABSTRACT FROM AUTHOR]

Electron relays play a crucial role for efficient light-induced activation by a photo-redox moiety of catalysts for multi-electronic transformations. Their insertion between the two units reduces detrimental energy transfer quenching while establishing at the same time unidirectional electron flow. This rectifying function allows charge accumulation necessary for catalysis. Mapping these events in photophysical studies is an important step towards the development of efficient molecular photocatalysts. Three modular complexes comprised of a Ru-chromophore, an imidazole electron relay function, and a terpyridine unit as coordination site for a metal ion were synthesized and the light-induced electron transfer events studied by laser flash photolysis. In all cases, formation of an imidazole radical by internal electron transfer to the oxidized chromophore was observed. The effect of added base evidenced that the reaction sequence depends strongly on the possibility for deprotonation of the imidazole function in a proton-coupled electron transfer process. In the complex with MnII present as a proxy for a catalytic site, a strongly accelerated decay of the imidazole radical together with a decreased rate of back electron transfer from the external electron acceptor to the oxidized complex was observed. This transient formation of an imidazolyl radical is clear evidence for the function of the imidazole group as an electron relay. The implication of the imidazole proton and the external base for the kinetics and energetics of the electron trafficking is discussed. [ABSTRACT FROM AUTHOR]

The [Re(bpy)(CO)3Cl] catalyst pioneered by Lehn for the two‐electron reduction of CO2 has constantly revealed unique facets in the mechanistic understanding of the selective transformation of CO2. A novel triazole‐linked ruthenium photosensitizer and a rhenium catalyst dyad was synthesized and investigated for photo‐induced charge accumulation using time‐resolved absorption spectroscopy. The triazole bridging ligand promoted weak electronic communication between the two units, resulting in an anodic shift of the reduction potentials of the Re moiety. Upon excitation of the photosensitizer, the first reduction of the catalyst occurred with a fast apparent rate of >5×107 s−1. Using a double‐excitation nanosecond pump‐pump‐probe setup to track the second electron accumulation on the catalytic unit was not conclusive as no observable absorption changes occurred upon the second excitation, suggesting a pathway for an efficient intramolecular reverse electron transfer preventing the two‐electron accumulation at the catalyst under our experimental conditions. Nevertheless, under continuous irradiation and with the use of sacrificial electron donors, photocatalytic CO2 reduction assays showed good turnover numbers, hinting at the non‐innocent role of byproducts in solution. [ABSTRACT FROM AUTHOR]

We have covalently connected the ruthenium trisbipyridine complex (bpyRu) as a photoredox module to an iron porphyrin catalyst (porFe) through an amido function for investigating the synergistic action to power the photocatalytic CO2 reduction. The electrochemical studies of the porFebpyRu dyad did not showany marked effect on the redox properties of the constitutive units.However, the photophysical properties of the porFe-bpyRu dyad point to the complete extinction of the photoredox module that undergoes ultrafast quenching processes with the porFe acolyte, the unavoidable dilemma in this type of molecular assemblies. Nevertheless, when exogenous bpyRu and a sacrificial electron donor were added to this dyad, we found that it exhibits much higher turnover number and selectivity towards CO2 photocatalytic reduction to CO than with the iron porphyrin analogue (porFe). Comprehensive analyses of the data suggest that this catalytic enhancement displayed by the dyad can be attributed to an interesting electron relay role played by the appended bpyRu moiety. [ABSTRACT FROM AUTHOR]

The manipulation of the second coordination sphere for improving the electrocatalytic CO2 reduction has led to breakthroughs with hydrogen bonding, local proton source, or electrostatic effects. We have developed two atropisomers of an iron porphyrin complex with two urea functions acting as multiple hydrogen‐bonding tweezers to lock the metal‐bound CO2 in a similar fashion found in the carbon monoxide dehydrogenase (CODH) enzyme. The αα topological isomer with the two urea groups on the same side of the porphyrin provides a stronger binding affinity to tether the incoming CO2 in comparison to the αβ disposition. However, the electrocatalytic activity of the αβ atropisomer outperforms its congener with one of the highest reported turnover frequencies at low overpotential. The strong H/D kinetic isotope effect (KIE) observed for the αα system indicates the existence of a tight water hydrogen‐bonding network for proton delivery which is disrupted by addition of an acid source. The small H/D KIE for the αβ isomer and the enhanced electrocatalytic performance on addition of stronger acid indicate the free access of protons to the bound CO2 on the opposite side of the urea arm. [ABSTRACT FROM AUTHOR]

The manipulation of the second coordination sphere for improving the electrocatalytic CO2 reduction has led to breakthroughs with hydrogen bonding, local proton source, or electrostatic effects. We have developed two atropisomers of an iron porphyrin complex with two urea functions acting as multiple hydrogen‐bonding tweezers to lock the metal‐bound CO2 in a similar fashion found in the carbon monoxide dehydrogenase (CODH) enzyme. The αα topological isomer with the two urea groups on the same side of the porphyrin provides a stronger binding affinity to tether the incoming CO2 in comparison to the αβ disposition. However, the electrocatalytic activity of the αβ atropisomer outperforms its congener with one of the highest reported turnover frequencies at low overpotential. The strong H/D kinetic isotope effect (KIE) observed for the αα system indicates the existence of a tight water hydrogen‐bonding network for proton delivery which is disrupted by addition of an acid source. The small H/D KIE for the αβ isomer and the enhanced electrocatalytic performance on addition of stronger acid indicate the free access of protons to the bound CO2 on the opposite side of the urea arm. [ABSTRACT FROM AUTHOR]

Inspired by the sulfur‐rich environment found in active hydrogenase enzymes, a Ni‐based proton reduction catalyst with pentadentate N2S3 ligand was synthesised. When coupled with [Ru(bpy)3]2+ (bpy=2,2′‐bipyridine) as photosensitiser and ascorbate as electron donor in a 1:1 mixture of dimethylacetamide and aqueous ascorbic acid/ascorbate buffer, the catalyst showed improved photocatalytic activity compared with a homologous counterpart bearing a tetradentate N2S2 ligand. The mechanistic pathway of photoinduced hydrogen evolution was comprehensively analysed through optical transient absorption and time‐resolved X‐ray absorption spectroscopy, which revealed important electronic and structural changes in the catalytic system during photoirradiation. The NiII catalyst undergoes a photoinduced metal‐centred reduction to form a NiI intermediate with distorted square‐bipyramidal geometry. Further kinetic analyses revealed differences in charge‐separation dynamics between the pentadentate and tetradentate forms. [ABSTRACT FROM AUTHOR]

Research in the development of new molecular catalysts for the selective transformation of CO2 to reduced forms of carbon is attracting enormous interest from chemists. Molecular catalyst design hinges on the elaboration of ligand scaffolds to manipulate the electronic and structural properties for the fine tuning of the reactivity pattern. A cornucopia of ligand sets have been designed along this line and more and more are being reported. In this quest, the porphyrin molecular platform has been under intensive focus due to the unmatched catalytic properties of metalloporphyrins. There have been rapid advances in this particular field during the last few years wherein both electronic and structural aspects in the second coordination spheres have been addressed to shift the overpotential and improve the catalytic rates and product selectivity. Metalloporphyrins have also attracted much attention in terms of the elaboration of hybrid materials for heterogeneous catalysis. Here too, some promising activities have made metalloporphyrin derivatives serious candidates for technological implementation. This review collects the recent advances centred around the chemistry of metalloporphyrins for the reduction of CO2. [ABSTRACT FROM AUTHOR]

The development of functional artificial photosynthetic devices relies on the understanding of mechanistic aspects involved in specialized photocatalysts. Modified iron porphyrins have long been explored as efficient catalysts for the light‐induced reduction of carbon dioxide (CO2) towards solar fuels. In spite of the advancements in homogeneous catalysis, the development of the next generation of catalysts requires a complete understanding of the fundamental photoinduced processes taking place prior to and after activation of the substrate by the catalyst. In this work, we employ a state‐of‐the‐art nanosecond optical transient absorption spectroscopic setup with a double excitation capability to induce charge accumulation and trigger the reduction of CO2 to carbon monoxide (CO). Our biomimetic system is composed of a urea‐modified iron(III) tetraphenylporphyrin (UrFeIII) catalyst, the prototypical [Ru(bpy)3]2+ (bpy=2,2'‐bipyridine) used as a photosensitizer, and sodium ascorbate as an electron donor. Under inert atmosphere, we show that two electrons can be successively accumulated on the catalyst as the fates of the photogenerated UrFeII and UrFeI reduced species are tracked. In the presence of CO2, the catalytic cycle is kick‐started providing further evidence on CO2 activation by the UrFe catalyst in its formal FeI oxidation state. [ABSTRACT FROM AUTHOR]

The development of functional artificial photosynthetic devices relies on the understanding of mechanistic aspects involved in specialized photocatalysts. Modified iron porphyrins have long been explored as efficient catalysts for the light‐induced reduction of carbon dioxide (CO2) towards solar fuels. In spite of the advancements in homogeneous catalysis, the development of the next generation of catalysts requires a complete understanding of the fundamental photoinduced processes taking place prior to and after activation of the substrate by the catalyst. In this work, we employ a state‐of‐the‐art nanosecond optical transient absorption spectroscopic setup with a double excitation capability to induce charge accumulation and trigger the reduction of CO2 to carbon monoxide (CO). Our biomimetic system is composed of a urea‐modified iron(III) tetraphenylporphyrin (UrFeIII) catalyst, the prototypical [Ru(bpy)3]2+ (bpy=2,2'‐bipyridine) used as a photosensitizer, and sodium ascorbate as an electron donor. Under inert atmosphere, we show that two electrons can be successively accumulated on the catalyst as the fates of the photogenerated UrFeII and UrFeI reduced species are tracked. In the presence of CO2, the catalytic cycle is kick‐started providing further evidence on CO2 activation by the UrFe catalyst in its formal FeI oxidation state. [ABSTRACT FROM AUTHOR]

Inspired by nature's orchestra of chemical subtleties to activate and reduce CO2, we have developed a family of iron porphyrin derivatives in to which we have introduced urea groups functioning as multipoint hydrogen‐bonding pillars on the periphery of the porphyrinic ring. This structure closely resembles the hydrogen‐bond stabilization scheme of the carbon dioxide (CO2) adduct in the carbon monoxide dehydrogenase (CODH). We found that such changes to the second coordination sphere significantly lowered the overpotential for CO2 reduction in this family of molecular catalysts and importantly increased the CO2 binding rate while maintaining high turnover frequency (TOF) and selectivity. Entrapped water molecules within the molecular clefts were found to be the source of protons for the CO2 reduction. [ABSTRACT FROM AUTHOR]

Inspired by nature's orchestra of chemical subtleties to activate and reduce CO2, we have developed a family of iron porphyrin derivatives in to which we have introduced urea groups functioning as multipoint hydrogen‐bonding pillars on the periphery of the porphyrinic ring. This structure closely resembles the hydrogen‐bond stabilization scheme of the carbon dioxide (CO2) adduct in the carbon monoxide dehydrogenase (CODH). We found that such changes to the second coordination sphere significantly lowered the overpotential for CO2 reduction in this family of molecular catalysts and importantly increased the CO2 binding rate while maintaining high turnover frequency (TOF) and selectivity. Entrapped water molecules within the molecular clefts were found to be the source of protons for the CO2 reduction. Like CODH: Urea groups at an iron porphyrin catalyst give multipoint hydrogen‐bonding stabilization resembling that found in the CO2 adduct of carbon monoxide dehydrogenase (CODH). The catalyst gave improved CO2 reduction to CO. Entrapped water molecules within the molecular clefts were found to be the source of protons for the CO2 reduction. [ABSTRACT FROM AUTHOR]

In this study we report a strategy to attach methylimidazolium fragments as ionic liquid units on an established iron porphyrin catalyst for the selective reduction of CO2 to CO. Importantly, we found that the tetra-methylimidazolium containing porphyrin exhibits an exalted electrocatalytic activity at low overpotential in water precluding the need for an external proton donor. [ABSTRACT FROM AUTHOR]

Abstract: A convenient and safe approach in valorizing carbon monoxide (CO) produced from the photocatalytic reduction of carbon dioxide (CO2) has been investigated. Visible light was used to drive an optimized photocatalytic reduction using a ruthenium trisbipyridine complex as a sensitizer and a rhenium bipyridyl carbonyl complex as a catalyst to perform an efficient reduction of CO2 to CO, which was then simultaneously utilized in a palladium‐catalyzed aminocarbonylation reaction at room temperature. This approach provides safe handling of the produced CO which also opens the way for a more efficient application of 13C‐isotope and 14C‐radioisotope‐labeled CO2 in pharmaceutically relevant drug labeling. [ABSTRACT FROM AUTHOR]

Inspired by the active site of CO dehydrogenase, a metalloporphyrin‐based mimic has been synthesized combining a multipoint hydrogen bond donor and a bimetallic active centre, as reported by Zakaria Halime, Ally Aukauloo, and co‐workers in their Communication (e202214665). The cooperativity between the two metal centres of the catalyst was shown for both homo‐ and heterobimetallic analogues, leading to a significant enhancement of the catalytic performance in the heterogeneous CO2‐to‐CO electrocatalytic reduction. [ABSTRACT FROM AUTHOR]

Back Cover: Bio-Inspired Bimetallic Cooperativity Through a Hydrogen Bonding Spacer in CO2 Reduction (Angew. Bimetallic Catalyst, Biomimetic, Carbon Dioxide, Electrocatalysis, Hydrogen Bonding Keywords: Bimetallic Catalyst; Biomimetic; Carbon Dioxide; Electrocatalysis; Hydrogen Bonding EN Bimetallic Catalyst Biomimetic Carbon Dioxide Electrocatalysis Hydrogen Bonding 1 1 1 02/10/23 20230213 NES 230213 B Inspired by the active site b of CO dehydrogenase, a metalloporphyrin-based mimic has been synthesized combining a multipoint hydrogen bond donor and a bimetallic active centre, as reported by Zakaria Halime, Ally Aukauloo, and co-workers in their Communication (e202214665). [Extracted from the article]

Inspired by the active site of CO dehydrogenase, a metalloporphyrin‐based mimic has been synthesized combining a multipoint hydrogen bond donor and a bimetallic active centre, as reported by Zakaria Halime, Ally Aukauloo et al. in their Communication (e202214665). The cooperativity between the two metal centres of the catalyst was shown for both homo‐ and heterobimetallic analogues, leading to a significant enhancement of the catalytic performance of the heterogeneous CO2‐to‐CO electrocatalytic reduction. [ABSTRACT FROM AUTHOR]

Keywords: Bimetallic Catalyst; Biomimetic; Carbon Dioxide; Electrocatalysis; Hydrogen Bonding EN Bimetallic Catalyst Biomimetic Carbon Dioxide Electrocatalysis Hydrogen Bonding 1 1 1 02/10/23 20230213 NES 230213 B Inspired by the active site b of CO dehydrogenase, a metalloporphyrin-based mimic has been synthesized combining a multipoint hydrogen bond donor and a bimetallic active centre, as reported by Zakaria Halime, Ally Aukauloo et al. in their Communication (e202214665). Bimetallic Catalyst, Biomimetic, Carbon Dioxide, Electrocatalysis, Hydrogen Bonding The cooperativity between the two metal centres of the catalyst was shown for both homo- and heterobimetallic analogues, leading to a significant enhancement of the catalytic performance of the heterogeneous CO SB 2 sb -to-CO electrocatalytic reduction. [Extracted from the article]

Unravelling the mechanism  of charge accumulation and utilization in the light‐driven carbon dioxide reduction using iron porphyrins bearing hydrogen bonding scaffolds revealed unprecedented puzzle pieces about its rate limiting step. While the formal Fe(0) redox state has been widely accepted as the catalytically active species, Zakaria Halime, Ally Aukauloo et al. show in their Communication (e202117530) that the Fe(I) species is already involved in the substrate activation of the photocatalytic cycle. [ABSTRACT FROM AUTHOR]

Cover Picture: Dissection of Light-Induced Charge Accumulation at a Highly Active Iron Porphyrin: Insights in the Photocatalytic CO2 Reduction (Angew. Carbon Dioxide, Iron, Mechanism, Photo-Reduction, Porphyrins Keywords: Carbon Dioxide; Iron; Mechanism; Photo-Reduction; Porphyrins EN Carbon Dioxide Iron Mechanism Photo-Reduction Porphyrins 1 1 1 03/23/22 20220328 NES 220328 B Unravelling the mechanism b of charge accumulation and utilization in the light-driven carbon dioxide reduction using iron porphyrins bearing hydrogen bonding scaffolds revealed unprecedented puzzle pieces about its rate limiting step. [Extracted from the article]

Titelbild: Dissection of Light-Induced Charge Accumulation at a Highly Active Iron Porphyrin: Insights in the Photocatalytic CO2 Reduction (Angew. Carbon Dioxide, Iron, Mechanism, Photo-Reduction, Porphyrins Keywords: Carbon Dioxide; Iron; Mechanism; Photo-Reduction; Porphyrins EN Carbon Dioxide Iron Mechanism Photo-Reduction Porphyrins 1 1 1 03/23/22 20220328 NES 220328 B Die Entschlüsselung des Mechanismus b der Ladungsakkumulation bei der lichtgetriebenen Kohlendioxidreduktion unter Verwendung von wasserstoffverbrückten Eisenporphyrinen liefert neue Einblicke in den geschwindigkeitsbegrenzenden Schritt. [Extracted from the article]

Molecular catalysts offer a unique opportunity to implement different chemical functionalities to steer the efficiency and selectivity for the CO2 reduction for instance. Metalloporphyrins and metallophthalocyanines are under high scrutiny since their most classic derivatives the tetraphenylporphyrin (TPP) and parent phthalocyanine (Pc), have been used as the molecular platform to install, hydrogen bonds donors, proton relays, cationic fragments, incorporation in MOFs and COFs, to enhance the catalytic power of these catalysts. Herein, we examine the electrocatalytic properties of the tetramethyl cobalt (II) tetrapyridinoporphyrazine (CoTmTPyPz) for the reduction of CO2 in heterogeneous medium when adsorbed on carbon nanotubes (CNT) at a carbon paper (CP) electrode. Unlike reported electrocatalysis with cobalt based phthalocyanine where CO was advocated as the two electron and two protons reduced intermediate on the way to the formation of methanol, we found here that CoTmTPyPz does not reduce CO to methanol. Henceforth, ruling out a mechanistic pathway where CO is a reaction intermediate. [ABSTRACT FROM AUTHOR]

Molecular catalysts offer a unique opportunity to implement different chemical functionalities to steer the efficiency and selectivity for the CO2 reduction for instance. Metalloporphyrins and metallophthalocyanines are under high scrutiny since their most classic derivatives the tetraphenylporphyrin (TPP) and parent phthalocyanine (Pc), have been used as the molecular platform to install, hydrogen bonds donors, proton relays, cationic fragments, incorporation in MOFs and COFs, to enhance the catalytic power of these catalysts. Herein, we examine the electrocatalytic properties of the tetramethyl cobalt (II) tetrapyridinoporphyrazine (CoTmTPyPz) for the reduction of CO2 in heterogeneous medium when adsorbed on carbon nanotubes (CNT) at a carbon paper (CP) electrode. Unlike reported electrocatalysis with cobalt based phthalocyanine where CO was advocated as the two electron and two protons reduced intermediate on the way to the formation of methanol, we found here that CoTmTPyPz does not reduce CO to methanol. Henceforth, ruling out a mechanistic pathway where CO is a reaction intermediate. [ABSTRACT FROM AUTHOR]

Cover Feature: Spectroscopic Characterisation of a Bio-Inspired Ni-Based Proton Reduction Catalyst Bearing a Pentadentate N2S3 Ligand with Improved Photocatalytic Activity (Chem. Eur. J. 13/2020) B The photocatalytic hydrogen production activity b of a novel bio-inspired pentadentate Ni catalyst was studied using complementary time-resolved spectroscopic techniques. Nickel, photochemistry, reaction mechanisms, time-resolved spectroscopy, X-ray absorption spectroscopy. [Extracted from the article]

CO2‐Reduktion Harnstoffgruppen in einem Eisenporphyrinkatalysator führen zu einer mehrfachen Stabilisierung von CO2 durch Wasserstoffbrücken. Wie Z. Halime, A. Aukauloo et al. in ihrer Zuschrift auf S. 4552 zeigen, hat der Katalysator eine hohe Aktivität in der CO2‐Reduktion. [ABSTRACT FROM AUTHOR]

CO2Reduction Urea groups in an iron porphyrin catalyst give multipoint hydrogen‐bonding stabilization of CO2. In their Communication on page 4504 ff., Z. Halime, A. Aukauloo et al. show that this catalyst enabled improved CO2 reduction. [ABSTRACT FROM AUTHOR]

The photocatalytic activity for CO 2 reduction of a series of Ni-substituted polyoxometalates (POMs) differing in nuclearity, shape and size, has been investigated under visible light irradiation, with [Ru(bpy) 3 ]2+ (bpy = 2,2′-bipyridine) as photosensitizer and triethanolamine as sacrificial donor. The tetrabutylammonium salt of the Ni 4 tetranuclear species was found to exhibit the highest CO production and its stability under photocatalytic conditions was demonstrated. The catalytic performance was significantly lower for the alkaline salt due to the separation of the POM from its counter-ions occurring only for the tetrabutylammonium salt. Photophysical experiments evidenced a bimolecular electron transfer from the reduced photosensitizer [Ru(bpy) 3 ]+ to the Ni 4 POM, the former arising from the reductive quenching of the [Ru(bpy) 3 ]2+ excited state by triethanolamine. This was further supported by DFT calculations, which also showed that the Ni 4 POM accumulates at least two electrons and four protons to carry out the CO 2 reduction catalytic process. [Display omitted] • Ni-based polyoxometalates are efficient catalysts for the CO2 conversion to CO under visible-light irradiation. • The tetrabutylammonium salt of the sandwich-type Ni4 POM has a 1.7-fold increase in activity compared with the alkaline salt. • The reduction of the catalyst by the [Ru(bpy)3]2 + /TEOA photochemical system proceeds via a reductive quenching pathway. • The Ni(II) centers act as catalytic active sites and the polyoxotungstate framework acts as a proton and electron reservoir. [ABSTRACT FROM AUTHOR]