A taxane 2-O-benzoyltransferase (mTBT, derived fromAccession #: AF297618) biocatalyzed the de-aroylation and re-aroylation of next-generation taxane precursors of drugs effective against multidrug-resistant cancer cells. Various taxanes bearing an acyl, hydroxyl, or oxo group at C13 were screened to assess their turnover by mTBT catalysis. The 13-oxotaxanes were the most productive where 2-O-debenzoylation of 13-oxobaccatin III was turned over faster compared to 13-oxo-10-O-(n-propanoyl)-10-O-deacetylbaccatin III and 13-oxo-10-O-(cyclopropane carbonyl)-10-O-deacetylbaccatin III, yielding ~20 mg of each. mTBT catalysis was likely affected by an intramolecular hydrogen bond with the C13-hydroxyl; oxidation to the 13-oxo recovered catalysis. The experimental data for the debenzoylation reaction was supported by Gaussian-accelerated molecular dynamics simulations that evaluated the conformational changes caused by different functional groups at C13 of the substrate. These findings also helped postulate where the 2-O-benzoylation reaction occurs on the paclitaxel pathway in nature. mTBT rearoylated the debenzoylated 13-oxobaccatin III acceptors fastest with a non-natural 3-fluorobenzoyl CoA among the other aroyl CoA thioesters evaluated, yielding ~10 mg of each with excellent regioselectivity at laboratory scale. Reducing the 13-oxo group to a hydroxyl yielded key modified baccatin III precursors (~10 mg at laboratory scale) of new-generation taxoids.

Pt-groups are the state-of-the-art electrocatalysts for various fuel cells. However, their CO-poising is a critical hitch for large-scale applications, so the researchers are exerting huge efforts to solve this issue. However, the exponentially increasing attention in this field pressures the researchers to publish their findings quickly, which somewhat leads to unavoidable flawed evaluation parameters to reflect the intrinsic activity of electrocatalysts. The CO oxidation (COOxid) is highly sensitive to various factors. Thus, it is urgent to afford a deeper understanding of the inherent COOxid activity of state-of-the-art electrocatalysts and adopt accurate guidelines for researchers to test, optimize, and compare their electrocatalysts. This review provides exactitude in the evaluation and precise assessment of the key descriptors related to electrocatalysts (i.e., effect of both size, shape, and support) and CO oxidation (i.e., effect of electrolyte, working electrode, and CO surface diffusion). This is besides the fundamental aspects (i.e., COOxid Process, mechanism, measurements, calculations, thermodynamics, and kinetics). Various experimental results from our group and others besides in-situ analysis were provided to support our deep discussion. Finally, we provide a brief synopsis of the relevant milestones of the up-to-date challenges and perspectives.

Transition metal-containing MFI-based catalysts are widely investigated in NH₃-SCR-DeNO _x and NH₃-SCO. Our review gives a critical overview of the influence of introducing mesopores on the catalyst activity and N₂ selectivity as well as the strategies for the development of ZSM-5 based catalysts with enhanced catalytic lifetime, supported by the investigations of reaction mechanisms.

Abstract

Transition metal-containing MFI-based catalysts are widely investigated in the selective catalytic reduction of NO _x with ammonia (NH₃-SCR-DeNO _x ), and the selective catalytic oxidation of ammonia (NH₃-SCO) into nitrogen and water vapor. While MFI-based catalysts are less intensively studied than smaller pore zeolites (i. e., chabazite, CHA) they are still used commercially for these processes and are of great interest for future study in particular to better understand structure-activity relationships. Hierarchically porous MFI catalysts (containing both micropores and mesopores) often show enhanced catalytic properties compared to conventional (microporous) materials in both NH₃-SCR-DeNO _x and NH₃-SCO. Thus, a critical overview of the current understanding of the salient physico-chemical properties that influence the performance of these catalysts is examined. Furthermore, strategies for the development of ZSM-5 based catalysts with enhanced catalytic lifetime, supported by the investigations of reaction mechanisms are reviewed and discussed.

This minireview summarizes the research advances on selective remote C−H bond activation through 1,5-palladium migration. The background, reaction scope, mechanistic rationale of each transformation and an outlook of future direction of related field are included.

Abstract

“Through space” metal/hydrogen shift constitutes one of the efficient elementary step in organometallic chemistry to achieve selective remote C−H bond functionalization. Compared with the relatively extensive exploration on 1,4-palladium migration, the processes on corresponding 1,5-palladium translocation are far less explored. Based on our understanding on related research areas, we summarized the advances achieved in remote C−H bond activation through a key step of 1,5-palladium migration in this minireview. The background, reaction scope, and more importantly, the mechanistic rationale of each transformation was discussed. We hope by reading through this minireview, one could get a general perspective on direct C−H bond activation via 1,5-palladium/hydrogen shift, and could understand why such a process is less common when compared with the process going through 1,4-palladium/hydrogen migration, and eventually could be inspired to develop practical ways for the synthesis of valuable molecules, which could not be prepared easily through other traditional approaches.

Electrochemical nitrogen reduction is considered a green strategy for ammonia synthesis, but its practical application is hindered by low ammonia yield rate and Faradaic efficiency. This review summarizes strategies to enhance the performance of ammonia synthesis from catalyst design, modulation of reaction interface and optimization of reaction system (including the lithium-mediated method), and proposes promising strategies and development directions for the future.

Abstract

The current industrial synthesis of ammonia involves an energy-intensive Haber-Bosch process, significantly contributing to a massive carbon footprint. An electrochemical synthetic pathway for nitrogen fixation has recently garnered significant attention. It allows ammonia production through a green process without generating harmful pollutants. However, due to the robust N≡N bond, the limited nitrogen solubility, and the competing reactions of hydrogen extraction, the synthesis of ammonia by electrochemical nitrogen reduction (e-NRR) is far from achieving industrialization. The intrinsic properties of the catalyst, the gas-solid-liquid interface, and the specific design of reaction system are the key factors that affect e-NRR performance. Therefore, this review discusses recent efforts in enhancing e-NRR performance towards ammonia production with regards to catalyst design, reaction interface optimization, and modulation of the reaction system (including lithium mediated ammonia synthesis). Finally, various promising research strategies and remaining tasks are presented. It is anticipated that this review could be beneficial for the further development of highly efficient and selective e-NRR to ammonia.

The Cover Feature illustrates an acceleration effect of novel anionic N-heterocyclic carbene (NHC) ligands in Pd-catalyzed cross-coupling reactions with unactivated aryl chlorides. In their Research Article, V. M. Chernyshev, V. P. Ananikov et al. report on the synthesis and catalytic activity studies of new base-ionizable NHCs and their Pd complexes that deprotonate in basic reaction media and, due to the negative charge on the NHC, significantly facilitate the oxidative addition of aryl chlorides compared to conventional NHCs of close steric bulkiness.More information can be found in the Research Article by V. M. Chernyshev, V. P. Ananikov et al.

We have demonstrated that bidentate pyridinophanes can be used as ligands for organometallic Ni complexes. These complexes exhibit unusual structural and electronic properties owing to the geometrically enforced anagostic interactions. These interactions were fully characterized and their impact on catalytic activity was evaluated.

Abstract

Herein, we report for the first time the use of the nitrogen-based bidentate molecule [2.2]pyridinophane (N2) as a ligand for metal complexes. Additionally, its improved synthesis allows for electronic modification of the pyridine rings to access the new para-dimethylamino-[2.2]pyridinophane ligand (p-NMe₂N2). These ligands bind nickel in an analogous fashion to other pyridinophane ligands, completing the series of tetra-, tri-, and bidentate pyridinophane-nickel complexes. The new compounds exhibit geometrically enforced C−H anagostic interactions between the ethylene bridge protons and the nickel center that are not present in other pyridinophane systems. These ethylene bridge groups also act as an unusual form of steric encumbrance, enforcing square planar geometries in ligand fields that would otherwise adopt tetrahedral structures. In addition, these anagostic interactions inhibit the catalytic performance in Csp³–Csp³ Kumada cross coupling reactions relative to other common bidentate N-ligand platforms, possibly by preventing the formation of the 5-coordinate oxidative addition intermediates.

We report the first case of amide hydrolysis on a rock-forming material, TiO₂, with insights into its surface activity. Amide hydrolysis at room temperature was achieved on TiO₂ with (001) surface, which is much lower than fluorine-modified (001) surface (>70 °C). The former surface follows the Lewis acid-catalyzed pathway, while the additional Brönsted acid sites induced by fluorine atoms on the latter one unexpectedly hindered the reaction.

Abstract

Amides are crucial components of biomolecules and are extensively used in polymer, pharmaceutical, and agrochemical production. Their direct hydrolysis offers great potential for exploring protein structures and producing valuable carboxylic acids in biological and industrial applications. Nevertheless, activating the resonance-stabilized C−N bond in amides poses a formidable challenge. Extensive research over the past decades has reported various transition metal-based complexes and solid catalysts that catalyze this reaction. These catalysts possess Lewis acid (LA) sites and exhibit enhanced activity when further combined with Brönsted acid (BA) sites. In this study, we present the first demonstration of amide hydrolysis on TiO₂, a rock-forming material, offering valuable insights into its surface activity. By using acetamide as the model compound, we observed that the thermodynamically stable (101) surface of TiO₂ remained inert up to 95 °C. Surprisingly, the high-energy (001) surface of TiO₂ activated amide hydrolysis at a temperature as low as 25 °C. Contrary to previous reports, the fluorine-modified (001) surface with additional BA sites required temperatures above 70 °C likely due to hydrogen bond stabilization by nearby fluorine atoms. These findings provide guidance for the development of cost-effective catalysts with improved activity.

A new approach to designing NHC ligands that enables significant facilitation of unactivated aryl halide oxidative addition in Pd/NHC-catalyzed reactions has been developed. Innovative NHC ligands enhancing Pd-catalyzed aryl chloride reactions are introduced. Leveraging steric and anionic properties, these 1,2,4-triazol-5-ylidene ligands improve efficiency in oxidative addition. Based on Nitron-type designs and NH-acidic groups, deprotonation of the ligand boosts electron donation, enhancing catalysis. The ATPr ligand, with 2,6-diisopropylphenyl groups, shows exceptional efficacy in various reactions, offering new insights for NHC design and metal-catalyzed processes.

Abstract

Aryl chlorides, due to their affordability and accessibility, are preferred reagents in Pd-catalyzed arylation reactions. However, the reactivity of aryl chlorides is often lower than that of aryl bromides and iodides due to the significantly higher barriers of the oxidative addition stage. This research introduces a novel design for NHC ligands, which notably enhances the efficiency of Pd/NHC catalytic systems in reactions where the oxidative addition of aryl chloride is the rate-limiting step. This design leverages the synergy between specific steric characteristics and the anionic nature of the newly fashioned 1,2,4-triazol-5-ylidene ligands. These ligands, inspired by Nitron-type designs, can be ionized under basic conditions due to their NH-acidic aryl(alkyl)amino groups. Detailed experimental and DFT studies revealed that the deprotonation of these NHCs promotes electron donation to the metal center, promoting the oxidative addition of aryl chloride. The specially optimized ATPr ligand, featuring 2,6-diisopropylphenyl groups, displayed remarkable catalytic efficacy in the Suzuki-Miyaura reaction and improved outcomes in ketone α-arylation and Buchwald-Hartwig reactions with unactivated aryl chlorides. The insights and strategies established in this study provide rational considerations for further advancements in NHC designs and their applications in metal-catalyzed reactions.

This concept highlights the recent advances in PEC selective glycerol oxidation for the preparation of multiple high value-added products, and discuss the reaction mechanism and selective production strategies in detail.

Abstract

The catalytic oxidation of glycerol, a surplus byproduct of biodiesel, has received increasing attention due to the popular applications of its oxidation products, such as aldehydes, ketones, and carboxylates. Photoelectrochemical (PEC) methods provide a clean and sustainable pathway for glycerol oxidation and upgrading. However, selective oxidation of glycerol is a challenge due to its complex oxidation path, where the cleavage of C−O or C−C bonds at different positions can lead to a variety of products. This concept aims to describe the recent advances in PEC selective glycerol oxidation for the preparation of multiple high value-added products, and discuss the reaction mechanism and selective production strategies in detail. Finally, the remaining challenges and future prospects for the PEC glycerol oxidation system are presented.