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The development of effective catalysts for the CO2 reduction reaction (CO2RR) is essential for transforming atmospheric CO2 into valuable chemical scaffolds. While numerous catalysts have been developed for the CO2RR, few are suitable for use in aqueous systems due to inherent design challenges. In this context, Covalent Organic Frameworks (COFs) have emerged as promising materials for the CO2RR in water, offering potential solutions to these challenges. Thanks to their porosity, high surface area and crystalline structure, COFs are excellent hosts for single-atom catalysts (SACs), enabling the immobilization of high-value species and their utilization in heterogeneous catalytic processes. For this reason, we have explored the catalytic activity of a terpyridine–manganese complex integrated into a COF lattice, which was successfully synthesized and characterized, confirming the presence of the metal ion in the material with spectroscopic techniques such as XPS and EDS. This new material has proved to be an active heterogeneous catalyst for the CO2RR in water as solvent, achieving a faradaic yield of 42% for CO at 300 mV overpotential and 16% for formate when 600 mV was applied. Furthermore, an ab initio theoretical study was performed to provide a plausible mechanism of the CO2RR to elucidate the CO evolution pathway. [ABSTRACT FROM AUTHOR]

Dichloromethane, as a readily available and inexpensive C1 synthon is proposed as a powerful building block for cyclopropanation of alkenes under mild conditions. Herein, we report a highly efficient and versatile dual photoredox system, involving a nickel aminopyridine coordination complex and a photocatalyst, for the cyclopropanation of aromatic olefins using dichloromethane, under visible‐light irradiation. The cyclopropanation protocol has been successfully applied at gram scale. Mechanistic studies suggest a Ni(II) pyridyl radical complex as the key intermediate for the homolytic cleavage of the Csp3−Cl bond, generating a chloromethyl radical that is captured by the olefin coupling partner. Our findings also highlight the versatility of this methodology. By directing the radical/polar crossover process, we were able to selectively drive the reaction towards either the formation of cyclopropyl derivatives or the corresponding non‐cyclic alkyl chloride products. The methodology also successfully apply to geminal dichloroalkanes, including the formation of spiro[2,2] compounds. Moreover, our methodology extends to the synthesis of deuterium‐labelled cyclopropanes, demonstrating its utility in isotopic labelling and broadening its applicability in chemical synthesis and drug development. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have become a versatile platform to immobilize a wide variety of single‐atom metal catalysts. The resulting post‐synthetic modified materials present a spectrum of valuable properties ranging from homogeneous to heterogeneous systems, such as well‐defined catalytic sites, selectivity, recyclability, and stability. In this minireview, we discuss selected contributions that provide experimental and computational details on reaction mechanisms (e. g., via EXAFS, TEM, and DFT) catalyzed by single‐atom metals embedded within the COF structure. When applicable, we highlight the different behaviour between molecular (homogeneous) and COF‐supported (heterogeneous) sites regarding catalytic performance. With this survey, we aim to decipher the key features that aid in seeing COFs as not merely passive supports but as active items in catalysis. [ABSTRACT FROM AUTHOR]

The construction of carbonyl compounds via carbonylation reactions using safe CO sources remains a long‐standing challenge to synthetic chemists. Herein, we propose a catalyst cascade Scheme in which CO2 is used as a CO surrogate in the carbonylation of benzyl chlorides. Our approach is based on the cooperation between two coexisting catalytic cycles: the CO2‐to‐CO electroreduction cycle promoted by [Fe(TPP)Cl] (TPP=meso‐tetraphenylporphyrin) and an electrochemical carbonylation cycle catalyzed by [Ni(bpy)Br2] (2,2′‐bipyridine). As a proof of concept, this protocol allows for the synthesis of symmetric ketones from good to excellent yields in an undivided cell with non‐sacrificial electrodes. The reaction can be directly scaled up to gram‐scale and operates effectively at a CO2 concentration of 10 %, demonstrating its robustness. Our mechanistic studies based on cyclic voltammetry, IR spectroelectrochemistry and Density Functional Theory calculations suggest a synergistic effect between the two catalysts. The CO produced from CO2 reduction is key in the formation of the [Ni(bpy)(CO)2], which is proposed as the catalytic intermediate responsible for the C−C bond formation in the carbonylation steps. [ABSTRACT FROM AUTHOR]

Two new tetradentate N4 ligands (LN4), LN4 = Me2,Me2PyzTACN (1-(2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl)-4,7-dimethyl-1,4,7-triazacyclononane) and Me2,MeImTACN (1-((1-methyl-1H-imidazol-1-yl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane) have been synthesized and their corresponding Fe(II) complexes [FeII(Me2,Me2PyzTACN)(CF3SO3)2], 1Pz, and [FeII(Me2,MeImTACN)(CF3SO3)2], 1Im, have been prepared and characterized. Complexes 1Pz and 1Im catalyse the hydroxylation of C–H bonds of alkanes with excellent efficiencies, using hydrogen peroxide as oxidant. The high H/D kinetic isotope effect values for C–H hydroxylation, large normalized tertiary/secondary C–H (C3/C2) bond selectivities in adamantane oxidation, and high degrees of stereoretention in the oxidation of cis-1,2-dimethylcyclohexane are indicative of metal-based oxidation processes. The complexes also catalyse the oxidation of cyclooctene to form its corresponding epoxide and syn-diol. For 1Pz the epoxide is the main product, while for the analogous complex 1Im the syn-diol predominates. The active oxidant is proposed to be an [(LN4)FeV(O)(OH)]2+ species (2Pz, LN4 = Me2,Me2PyzTACN and 2Im, LN4 = Me2,MeImTACN) which may exist in two tautomeric forms related by a proton shift between the oxo and hydroxo ligands. Isotope labelling experiments show that the oxygen atom in the hydroxylated products originates from both water and hydrogen peroxide, and labelling experiments involving oxygen atom transfer to sterically bulky substrates provide indirect information on the steric influence exerted by the two ligands in the relative reactivities of the two hypervalent iron tautomers. Based on these labelling studies, the steric influence exerted by each of the ligands towards the relative reactivity of the oxo ligands of the corresponding pair of Fe(V)(O)(OH) tautomers can be derived. Furthermore, this steric influence can be gauged relative to related complexes/ligands. [ABSTRACT FROM AUTHOR]

The reactivity of metal complexes can be primarily controlled by their coordinating ligands. Electronic effects and geometric restrictions imposed by ligands, prototypically modify their reactivity, but are not always straightforward accessible. In the course of the study, we explored new C3‐symmetric organometallic nickel (II) complexes ((P3C)Ni)) with the particularity of having a metalated apical carbon trans to a labile coordination site readily available as a catalytic site. The synthetic methodology allowed to tune the electronic properties by introducing substituents on the phosphines. We studied the nature of the C−Ni bond by X‐ray absorption spectroscopy (XAS) and DFT and applied them to the catalytic hydrogenation of quinolines with a good chemical scope and group tolerance. 1H‐NMR monitoring, isotopic labelling, and computational studies are consistent with a heterolytic activation of the dihydrogen molecule after forming a σ‐H2 adduct trans to the metalated carbon. [ABSTRACT FROM AUTHOR]

The inertness of chloroalkanes has precluded them as coupling partners for cross‐coupling reactions. Herein we disclose a general strategy for the activation of inert alkyl chlorides through photoredox catalysis and their use as coupling partners with alkenes. The catalytic system is formed by [Ni(OTf)(Py2Tstacn)](OTf) (1Ni), which is responsible for the Csp3−Cl bond activation, and [Ir(NMe2bpy)(ppy)2]PF6, (PCIrNMe2), which is the photoredox catalyst. Combined experimental and theoretical studies show an in situ photogenerated NiI intermediate ([Ni(Py2Tstacn)]+) which is catalytically competent for the Csp3−Cl bond cleavage via a SN2 mechanism for primary alkyl chlorides, forming carbon‐centered free radicals, which react with the olefin leading to the formation of the Csp3−Csp3 bond. These results suggest inert alkyl chlorides can be electrophiles for developing new intermolecular strategies in which low‐valent aminopyridine nickel complexes act as key catalytic species. [ABSTRACT FROM AUTHOR]

In this study, we combine in situ spectroelectrochemistry coupled with electron paramagnetic resonance (EPR) and X‐ray absorption spectroscopies (XAS) to investigate a molecular Ru‐based water oxidation catalyst bearing a polypyridinic backbone [RuII(OH2)(Py2Metacn)]2+. Although high valent key intermediate species arising in catalytic cycles of this family of compounds have remain elusive due to the lack of additional anionic ligands that could potentially stabilize them, mechanistic studies performed on this system proposed a water nucleophilic attack (WNA) mechanism for the O−O bond formation. Employing in situ experimental conditions and complementary spectroscopic techniques allowed to observe intermediates that provide support for a WNA mechanism, including for the first time a Ru(V) oxo intermediate based on the Py2Metacn ligand, in agreement with the previously proposed mechanism. [ABSTRACT FROM AUTHOR]

CO2 electroreduction could be improved by applying conceptualized strategies to overcome catalytic bottlenecks. In this regard, we report two new cobalt(II) complexes [Co(Py2RN3)(OTf)](OTf) (CoR, R=H, Me) based on a new C2‐symmetric pentacoordinate chiral ligand that are active on the electrochemical CO2 reduction to CO. One of the complexes has a N−H group oriented towards the CO2 binding site (CoH), while the other has a N−Me group with the same orientation (CoMe), as showed by X‐ray diffraction. We have studied the effect of introducing hydrogen bonding sites, i. e. N−H in CoH, as a strategy to stabilize reaction intermediates. The complex bearing coordinating unprotected N−H group (CoH) displays catalytic CO2 reduction at the CoII/I redox potential (−1.9 V vs. Fc, ca. 40 % FYCO) whereas CoMe shows CO2 reduction at the CoI/0 redox pair. FTIR‐SEC and DFT calculations identified a [CoI−CO]+ cation as catalytic intermediate. The beneficial effect of the N−H group has been attributed to the stabilization of reaction intermediates or transition states and by the larger electron‐donating capacity, thus enhancing the nucleophilic character of the CoI intermediate. The study also points to the CO dissociation from the Co(I)−CO resting state intermediate as one of the bottlenecks of the catalytic cycle, which can be overcome with light irradiation, resulting in an increase of the total CO production (−1.9 V, 81 % FYCO, 11.2 TONCO) at the CoII/I redox potential. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) is a fundamental process to develop a technology that can drive energy transition towards renewable and sustainable fuels. Nevertheless, efficient and straightforward methodologies to obtain superior and stable electrodes need to be implemented to approach this technology to real applications. Recently, self-supported catalysis emerged as a promising solution. However, catalyst design is still limited by the low chemical tunability and elevated preparation times and costs. Herein, a solution combustion (SC) methodology is described to produce designed self-supported electrocatalysts that excel in the OER and mitigate previous limitations. M-doped NiO-based electrocatalysts (with M = Fe, Co, Mn, and Zn) were self-supported by the SC method on nickel foam, and overperformed analogous benchmarked catalysts prepared by other methods. Notably, in Fe-doped NiO, the overpotential required to drive the OER at 10 mA cm−2 was found to be 190 mV, the lowest reported so far for metal oxide electrocatalysts at pH 13. By the combination of spectroelectrochemical (SEC) and electrochemical impedance spectroscopy (EIS), we studied the role of the metal dopant cation, showing that dopant metals assist the formation of the active species responsible for the high (electro)catalytic activity. We envision that the presented simple, cost-time efficient methodology would stimulate the preparation and study of effective self-supported metal-oxide catalysts for a broad range of applications. [ABSTRACT FROM AUTHOR]

Postmodification of reticular materials with well‐defined catalysts is an appealing approach to produce new catalytic functional materials with improved stability and recyclability, but also to study catalysis in confined spaces. A promising strategy to this end is the postfunctionalization of crystalline and robust metal–organic frameworks (MOFs) to exploit the potential of crystal‐to‐crystal transformations for further characterization of the catalysts. In this regard, two new photocatalytic materials, MOF‐520‐PC1 and MOF‐520‐PC2, are straightforwardly obtained by the postfunctionalization of MOF‐520 with perylene‐3‐carboxylic acid (PC1) and perylene‐3‐butyric acid (PC2). The single crystal‐to‐crystal transformation yielded the X‐ray diffraction structure of catalytic MOF‐520‐PC2. The well‐defined disposition of the perylenes inside the MOF served as suitable model systems to gain insights into the photophysical properties and mechanism by combining steady‐state, time‐resolved, and transient absorption spectroscopy. The resulting materials are active organophotoredox catalysts in the reductive dimerization of aromatic aldehydes, benzophenones, and imines under mild reaction conditions. Moreover, MOF‐520‐PC2 can be applied for synthesizing gram‐scale quantities of products in continuous‐flow conditions under steady‐state light irradiation. This work provides an alternative approach for the construction of well‐defined, metal‐free, MOF‐based catalysts. [ABSTRACT FROM AUTHOR]

We demonstrate here the suitability of CsPbBr3 nanoparticles as photosensitizers for a demanding photoredox catalytic homo- and cross-coupling of alkyl bromides at room temperature by merely using visible light and an electron donor, thanks to the cooperative action between the nanoparticle surface and organic capping. [ABSTRACT FROM AUTHOR]

Nonactivated alkyl chlorides are readily available and bench-stable feedstocks; however, they exhibit an inherent chemical inertness, in part, due to their large negative reduction potentials, which have precluded their widespread use as radical precursors in visible-light photocatalysis. Herein, we highlight some recent strategies for activating challenging organic halides under light irradiation, with special emphasis in C(sp3)–halide bonds. In this line, a brief summary of the reactivity of Vitamin B12 , F430 cofactor and derivatives is required to comprehend the chemistry behind our developed Cu/M (M = Co, Ni) dual catalytic system. Catalyst design has been key for developing a mild and general photoredox methodology for the intramolecular reductive cyclization of nonactivated alkyl chlorides with tethered alkenes. The cleavage of strong C(sp3)–Cl bonds is mediated by a highly nucleophilic low-valent cobalt or nickel intermediate generated by visible-light photoredox reduction employing a copper photosensitizer. [ABSTRACT FROM AUTHOR]

The chemical inertness of abundant and commercially available alkyl chlorides precludes their widespread use as reactants in chemical transformations. Presented in this work is a metallaphotoredox methodology to achieve the catalytic intramolecular reductive cyclization of unactivated alkyl chlorides with tethered alkenes. The cleavage of strong C(sp3)−Cl bonds is mediated by a highly nucleophilic low‐valent cobalt or nickel intermediate generated by visible‐light photoredox reduction employing a copper photosensitizer. The high basicity and multidentate nature of the ligands are key to obtaining efficient metal catalysts for the functionalization of unactivated alkyl chlorides. The chemical inertness of abundant and commercially available alkyl chlorides precludes their widespread use as reactants in chemical transformations. Presented here is a methodology to achieve the catalytic intramolecular reductive cyclization of unactivated alkyl chlorides with tethered alkenes. The cleavage of strong C(sp3)−Cl bonds is mediated by either a highly nucleophilic low‐valent cobalt or nickel intermediate, generated by employing a copper photosensitizer in a visible‐light photoredox reduction. [ABSTRACT FROM AUTHOR]

Cobalt(ii) complexes with the general structure [CoII(OTf)(Y,XPy2Tstacn)](OTf) (1R, where Y,XPy2Tstacn is 1,4-di(p-Y,m-X-picolyl)-7-R-1,4,7-triazacyclononane; 1H, 1CO2Et, 1DMM) and [CoII(OTf)2(Y,XPyMetacn)] (2R, where Y,XPyMetacn is 1-(p-Y,m-X-picolyl)-7,4-di-methyl-1,4,7-triazacyclononane; 2CO2Et, 2Cl, 2H, 2DMM, 2NMe2) were active in both light-driven acetophenone (3a) and water reduction. Competition studies show that aromatic ketone/water reduction selectivity ranks from 0.2 to 8.0. Nevertheless, considering the concentrations of water and ketone in catalysis (ratio H2O/3a∼ 2000) the highest selectivity obtained is greater than 15 000. The selectivity correlates well with the CoI/II redox potential within the same cobalt catalyst series (span 240 mV (1R) and 290 mV (2R)), with electron donating ligands favoring ketone reduction over H2 evolution. Based on this finding, the operative mechanism for the reduction of aromatic ketones is consistent with a single electron transfer (SET) followed by a hydrogen atom transfer (HAT) mechanism. This new insight will be a guide to develop selective catalytic systems to produce fine solar chemicals in water. [ABSTRACT FROM AUTHOR]

Abstract: Well‐defined manganese(I) carbonyl complexes bearing bis‐N‐heterocyclic carbene (NHC) ligands are shown to be effective catalysts for the reduction of carbonyl groups through hydrosilylation reactions. A wide variety of ketones are selectively reduced to the corresponding alcohols by using phenylsilane, and the cheap and readily abundant polymethylhydrosiloxane (PMHS) in the presence of catalytic amounts of MnI organometallic complexes. Interestingly, α,β‐unsaturated ketones and dialkyl ketones are selectively reduced. Mechanistic studies based on radical scavengers suggest the involvement of radical species in the catalytic reaction. [ABSTRACT FROM AUTHOR]

We present the first example of non‐classical hydrogen bonding in CuI complexes. To this end, we have studied the coordination capacity of the tripodal phosphine ligands HTIM(PR2)3 {tris[1‐(di‐R‐phosphanyl)‐3‐methyl‐1H‐indol‐2‐yl]methane, R = Ph, iPr} towards copper, leading to a series of eight CuI complexes [{HTIM(PR2)3}CuX] [R = Ph (1–4), iPr (5–8); X = Cl–, I–, OTf–, BF4–]. An anagostic interaction in the CuI complexes has been proposed based on the results of 1H NMR, ultrahigh‐resolution X‐ray diffraction, and theoretical [atoms‐in‐molecules (AIM) and natural bonding orbital (NBO)] analyses of the electron density. Among the different synthesized complexes, [{HTIM(PPh2)3}CuOTf] (2) shows the strongest Cu···H–C interaction with a linear geometry (179.98°) and the shortest distance described so far [d(Cu–H) = 1.9 Å] in its toluene solvated form. Both parameters are characteristic of 3c–4e– interactions. In addition, we have found that these tripodal ligands exhibit unprecedented selectivity towards CuI ions. The synthesized HTIM(PR2)3CuI complexes have been found to be catalytically active and selective for the hydroboration of CO2 to formic acid. [ABSTRACT FROM AUTHOR]

Abstract: We report here the first purely organometallic fac‐[MnI(CO)3(bis‐MeNHC)Br] complex with unprecedented activity for the selective electrocatalytic reduction of CO2 to CO, exceeding 100 turnovers with excellent faradaic yields (ηCO≈95 %) in anhydrous CH3CN. Under the same conditions, a maximum turnover frequency (TOFmax) of 2100 s−1 was measured by cyclic voltammetry, which clearly exceeds the values reported for other manganese‐based catalysts. Moreover, the addition of water leads to the highest TOFmax value (ca. 320 000 s−1) ever reported for a manganese‐based catalyst. A MnI tetracarbonyl intermediate was detected under catalytic conditions for the first time. [ABSTRACT FROM AUTHOR]

Abstract: Commercial carbon fibers can be used as electrodes with high conductive surfaces in reduced devices. Oxidative treatment of such electrodes results in a chemically robust material with high catalytic activity for electrochemical proton reduction, enabling the measurement of quantitative faradaic yields (>95 %) and high current densities. Combination of experiments and DFT calculations reveals that the presence of carboxylic groups triggers such electrocatalytic activity in a bioinspired manner. Analogously to the known Hantzsch esters, the oxidized carbon fiber material is able to transfer hydrides, which can react with protons, generating H2, or with organic substrates resulting in their hydrogenation. A plausible mechanism is proposed based on DFT calculations on model systems. [ABSTRACT FROM AUTHOR]