The development of base metal electrodes that can act as active and stable oxygen generating electrodes in water electrolysis systems, especially at low pH levels, remains a challenge. The use of suspensions as electrolytes for water splitting has until recently been limited to photoelectrocatalytic approaches. A high current density (j=30 mA/cm2) for water electrolysis has been achieved at a very low oxygen evolution reaction (OER) potential (E=1.36 V vs. RHE) using a SnO2/H2SO4 suspension-based electrolyte in combination with a steel anode. More importantly, the high charge-to-oxygen conversion rate (Faraday efficiency of 88% for OER at j=10 mA/cm2 current density). Since cyclic voltammetry (CV) experiments show that oxygen evolution starts at a low, but not exceptionally low, potential, the reason for the low potential in chronoamperometry (CP) tests is an increase in the active electrode area, which has been confirmed by various experiments. For the first time, the addition of a relatively small amount of solids to a clear electrolyte has been shown to significantly reduce the overpotential of the OER in water electrolysis down to the 100 mV region, resulting in a remarkable reduction in anode wear while maintaining a high current density.

Ceria surface reduction leads to non-monotonic trends in ethene hydrogenation rates due to site requirements stipulating a balance between reduced and oxidized sites. The sensitivity of hydrogenation rates to surface reduction can be tuned by varying ceria surface termination.

Abstract

The precise effect of oxide understoichiometry on bulk oxide catalytic properties continues to remain a subject of intense investigation. Of specific interest in this regard is the role of oxygen vacancies present on bulk ceria catalysts that have recently been reported to represent a more cost-effective alternative to the more toxic and expensive catalysts used industrially for the selective hydrogenation of acetylene to ethylene. Contrasting claims as to the effect of surface reduction on hydrogenation rates exist in the open literature, with vacancy formation attributed, in separate studies, either a favorable or a deleterious role in effecting hydrogenation turnovers. We report here the non-monotonic behavior of ethene hydrogenation rates that subsumes both of these trends as a function of degree of surface reduction over a sufficiently large range of pre-reduction temperatures. Steady state transient kinetic and isotopic exchange data combined with in-situ titration experiments suggest that this non-monotonic trend can be attributed not to a change in either the kinetic relevance of specific elementary steps or the hydrogenation mechanism, but rather to site requirements that stipulate the need for two distinct, proximal sites. We also show that the sensitivity of hydrogenation rates to surface reduction can be altered by varying ceria surface termination, with the more open (110) and (100) surfaces exhibiting a less asymmetric effect of surface reduction on ethene hydrogenation rates.

This Concept paper summarizes the recent advances in metal-organic framework (MOF) based hydrogen atom transfer catalysis. Design principles, effects and advantages of MOF platform, and current limitations are discussed.

Abstract

This concept paper aims to summarize recent research on the design and synthetic applications of metal-organic frameworks (MOFs)-based hydrogen atom transfer (HAT) catalysts. Functional MOFs have emerged as highly promising heterogeneous catalysts, leveraging their tunable, ordered structure and abundant active sites to enhance catalytic efficiency in various reactions. HAT, a versatile method for generating active open-shell radical species through selective hydrogen abstraction, has been well explored in homogeneous photocatalysis. In contrast, heterogeneous HAT catalysis remains less developed, albeit their great potential in industry. This paper will provide a timely overview of the advancements in MOFs-based HAT photocatalysis, classified according to catalytic centers including aromatic ketones, polyoxometalates, xanthene dyes, thiols, and alcohols, highlighting their design principles and practical applications in photocatalytic organic synthesis.

Polyoxometalate-based frameworks, as a kind of material combined both the advantages of oxygen-rich polyoxometalates (POMs) and porous metal-organic frameworks (MOFs) within one single system, could serve as potential photocatalysts with diverse structure features. This review focus on the recent development based on the POM-based frameworks along with their construction strategies and applications in various areas of photocatalysis, mainly including water splitting, CO₂ reduction, organic synthesis and also the selective coupling reactions.

Abstract

Polyoxometalate-based frameworks, as a kind of material constructed by polyoxometalates (POMs), metal ions or clusters, organic ligands, are combined both the advantages of oxygen-rich POMs and porous metal-organic frameworks (MOFs) within one single system. This integration greatly expands their potential applications compared to the individual POMs or MOFs. Particularly for photocatalysis, the narrow light absorption range of the typical POMs units in the ultraviolet region hinders their extensive uses as visible-light-driven photocatalysts. However, the incorporation of photoactive units into POMs-based frameworks can be considered as an effective approach to overcome this limitation. In this paper, we review selected examples of recent progress based on the POM-based frameworks along with their construction strategies and applications in various areas of photocatalysis, mainly including water splitting, CO₂ reduction, organic synthesis and also the selective coupling reactions.

The effects of oxygen functionalities on GNP (Graphene Nanoplatelets) has been investigated, functionalizing GNP in liquid phase using different oxidants (HNO₃, H₂O₂, KMnO₄), with the aim to tune the amount and the type of oxygen functionalities. Pd NPs have been deposited on the different functionalized carbon supports to be tested in benzaldehyde hydrogenation/hydrogenolysis to benzyl alcohol and toluene as model reaction.

Abstract

This paper presents a study on the effects of oxygen functionalities on a mesoporous and graphitized carbon support (GNP, Graphene Nanoplatelets), on the catalytic activity of Pd/GNP catalysts in hydrogenation reactions. A functionalization method in liquid phase has been employed, using different oxidants (HNO₃, H₂O₂, KMnO₄), with the aim to tune the amount and the type of introduced oxygen functionalities. Preformed Pd nanoparticles have been used as Pd-precursor to limit differences in metal particle size and dispersion on differently functionalized carbon. The catalytic behaviour in benzaldehyde hydrogenation/hydrogenolysis to benzyl alcohol and toluene revealed that the introduction of oxygen functionalities has a generally detrimental effect. NMR relaxometry studies highlighted the weaker interaction between the carbonyl group and the functionalized Pd/GNP surface than the non–functionalized Pd/GNP demonstrating that the origin of the different catalytic activity lies on the first step of the reaction. O-functionalities also impacted on the Pd⁰/Pd²⁺ ratio at the surface which is an established parameter correlated to the reaction rate.

Small, strained carbocyclic systems have fascinated organic chemists from both a theoretical and synthetic standpoint. These systems often challenge conventional wisdom when it comes to molecular structure and tactics for chemical construction. The cyclopropyl motif is one such ring system that remains at the forefront of method development in the modern era. With the advent of an array of non-traditional building blocks, a range of new cyclopropanation processes using one- and two-electron strategies have been developed that not only overcome the synthetic shortcomings of classical approaches but also provide entry into a wide range of new classes of cyclopropanes. This review discusses recent advances in this area with an emphasis on their mechanistic underpinnings and potential applications. Additionally, a concise overview of the properties of and traditional approaches to cyclopropanes is provided.

The ternary copolymerization of a series of cyclic anhydrides with epoxides and carbon dioxide using dinuclear [OSSO]-type chromium (III),1, and -iron(III), 2, complexes (0.1 mol%) in combination with (bis(triphenylphosphine)iminium chloride) (PPNCl, 0.5-1.0 mol with respect to catalyst) as co-catalyst is reported in this study. The results have yielded copolymers with polyester and polycarbonate segments with high molecular weights and narrow dispersity. The catalytic systems 1-2/PPNCl were tested in the copolymerization of different epoxides, such as propylene oxide (PO), cyclohexene oxide (CHO), and vinylcyclohexene oxide (VCHO), with a variety of cyclic anhydrides, such as phthalic (PA), diglycolic (DGA) and succinic (SA), with CO2 pressure of 20 bar, temperature range of 45-80 °C in 24 h. Anhydride reaction, affording the polyester segments, exceeded the conversion of 99% in all the explored cases. On the other hand, in the case of epoxide copolymerization with CO2, for the propylene oxide (PO) reaction, the selectivity towards polypropylene carbonate (PPC) without polyether linkage consistently was >99%. For the terpolymerization of PO, CO2 and diglycolic anhydride (DGA), a notable epoxide conversion of 86%, selectively to polycarbonate, with TOF value as high as 36 h-1, was achieved.

The increasing use of fluorine-containing bioactive molecules necessitates efficient strategies for fluorinated group installation. Despite the impressive development of photoinduced radical fluoroalkylation as a powerful tool for introducing fluorine, the persistent issues, including the recyclability and reaction specificity of homogeneous photocatalysts, still leave great room for further advancement in a sustainable and general fashion. Herein, we report a conceptually different approach toward multiple types of fluoroalkylations by using recoverable and versatile graphitic carbon nitride (g-CN) nanosheets as a heterogeneous photocatalyst. This photocatalytic system enables diverse intermolecular fluoroalkylations of alkenes with fluoroalkanesulfinates and intramolecular fluoroalkyl migrations of alkenyl triflates. Detailed characterizations and mechanism studies substantiate the stability of this organic semiconductor and the crucial role of photogenerated electron-hole pairs.

Salvinorin A, a potent human hallucinogen, uniquely activates the kappa-opioid receptor (κ-OR) with high efficacy and selectivity. Its novel structure lacks nitrogenous components, distinguishing it from other opioids. With a complex trans-decalin core and δ-lactone fused with a furan moiety, synthetic access to Salvinorin A remains challenging due to a sensitive epimerizable center. Despite considerable synthetic efforts, only nine syntheses have been produced. This review aims to offer insights into the primary strategies employed to accomplish the syntheses documented thus far.

Abstract

Salvinorin A is a powerful hallucinogen in humans, and a selective, high efficacy agonist of the kappa-opioid receptor (κ-OR). Salvinorin A is the first plant-derived ligand with high selectivity for κ-OR over other receptors, its structure is unrelated to any known opioid receptor ligands, even lacking any nitrogenous moieties. Mechanistically and pharmacologically, salvinorin A is distinct from other known hallucinogens in humans, making it the only selective κ-OR ligand to gain wide-spread interest outside of research. Structurally, salvinorin A bares a highly functionalized trans-decalin core, containing two quaternary centers, and is fused to a δ-lactone baring a furan moiety. Synthetic access of salvinorin A has been elusive due to a highly sensitive epimerizable center at carbon 8 (C8). All these features make salvinorin A a highly challenging synthetic target. With multiple synthetic efforts from around the world, only nine completed syntheses have been achieved to date. This review is intended to provide a look at the key strategies used to achieve the syntheses reported to date. We will summarize the efforts towards the syntheses of salvinorin A starting from Evans in 2007 to Barriault in 2023.

High catalytic performance of the iridium-polymer complex for the dehydrogenative oxidation of alcohols was demonstrated. Bipyridonate moiety in the polymer structure acts as a cooperative “functional ligand”, realizing the enhancement of dehydrogenation of various alcohols. Further, recovered catalyst could be reused without loss of catalytic efficiency at least ten times.

Abstract

A series of iridium-polymer complexes containing bipyridonate moieties were synthesized. The high catalytic performance of the iridium-polymer complex for the dehydrogenative oxidation of alcohols was demonstrated. Notably, the bipyridonate moiety in the polymer structure acts as a chemically non-innocent “functional ligand”, realizing the enhancement of dehydrogenation process. While numerous metal-polymer catalysts have been reported so far, to our knowledge, introducing a “functional ligand” into a polymer chain that can operate cooperatively with transition metals by changing their structures during the catalytic processes is rare. The iridium-polymer complex could be easily separated from the product and recovered by precipitation upon the addition of methanol after the catalytic reaction. Furthermore, the recovered catalyst could be reused without loss of catalytic efficiency at least ten times.