Finn Moeller

A nanoflower-like CuFe-based electrocatalysts on copper foam (CF) substrates (CuFeO_x/CF) was fabricated, which achieving a DHMF selectivity of 93.3 % and a yield of 90.1 % in the electrocatalytic hydrogenation of HMF. Introducing Fe plays a role in regulating the electronic structure of Cu site, facilitating the generation of H* and adsorption of HMF, thus hampering the occurrence of dimerization.

Abstract

Converting biomass-derived 5-hydroxymethylfurfural (HMF) into high-valued 2,5-dihydroxymethylfurfural (DHMF) via electrocatalytic hydrogenation (ECH) technology has been widely regarded as one of the most economical and eco-friendly routes. The high selectivity and activity depend on the reasonable regulation of the adsorption and activation of adsorbed hydrogen (H*) and HMF on the surface of the electrocatalyst. Herein, we report nanoflower-like CuFe-based electrocatalysts on copper foam (CF) substrates (CuFeO_x/CF). DHMF was achieved on the optimal CuFeO_x/CF with a selectivity of 93.3 % and a yield of 90.1 %. The H*, HMF and product were observed by in situ attuned total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Moreover, in situ Raman spectra discloses the reconstruction of catalyst into CuFe-bimetal with low valence state. Density functional theory (DFT) calculations demonstrate that introducing Fe plays a role in regulating the electronic structure of Cu sites, which facilitate the generation of H* and adsorption of HMF, thus hampering the occurrence of dimerization. This study provides an innovative idea for the rational design of non-precious bimetallic electrocatalysts for ECH to produce high-valued chemicals.

The Cover Feature depicts the artificial photosynthesis process from CO₂ and water to 6-undecanone, starting with the electrochemical generation of syngas followed by its fermentation to give hexanoic acid and its decarboxylative ketonization to the C₁₁ building block 6-undecanone. All steps are in the pilot plant stage, as illustrated by the reactor on the right-hand side. When conducted in flow on a manganese sipernat catalyst, the decarboxylative ketonization step reaches 99.99 % yield at a productivity of 1.1 kg L⁻¹ h⁻¹. More information can be found in the Research Article by L. J. Gooßen and co-workers.

Nature Communications, Published online: 20 July 2024; doi:10.1038/s41467-024-50596-3

A novel green solvent, γ-valerolactone (GVL), efficiently facilitates the photocatalytic activation of C−H bonds in benzylic compounds. Mechanistic studies reveal that GVL′s high dielectric constant (ϵ) increases the driving force (−ΔG), and its large refractive index (n) reduces reorganization energy (λ), collectively reducing the reaction barrier (ΔG ^≠). This research advances the overlooked solvent effects in semiconductor photocatalysis.

Abstract

Solvents can significantly influence chemical reactions in condensed phases. Their critical properties are increasingly recognized in various research domains such as organic synthesis and biomass valorization. However, in semiconductor photocatalysis, solvents are primarily viewed as mediums for dissolving and diffusing substances, with their potential beneficial effects on photocatalytic conversions often overlooked. Additionally, common photocatalysis solvents like acetonitrile (ACN) pose serious safety and environmental concerns. In this study, we demonstrate that novel and safe green solvents, such as γ-valerolactone (GVL), can significantly enhance the performance of semiconductor photocatalysis for C−H bond activation. Non-specific solvent-solute interactions are the primary contributors to increased photocatalytic activity in the self-coupling of benzylic compounds. Specifically, GVL′s large dielectric constant and high refractive index lower the energy barrier for the rate-determining C−H bond activation step, facilitating a faster coupling reaction. The versatility of GVL is further demonstrated in reactions with multiple reagents and in various oxidation and reduction photocatalytic systems beyond classic C−H bond activation. This work not only pioneers the use of green solvents but also provides comprehensive insights for proper solvent selection in semiconductor photocatalysis.

This research article presents two new benign methodologies to access reactive and soluble lignin-based polyamines. The aminated lignin products have potential as renewable building blocks in aromatic polymeric materials or as potential chelating, antibacterial agents, for instance.

Abstract

Lignin is a widely available second-generation biopolymer and the main potential source of renewable aromatic building blocks. Lignin-based polyamines offer great potential in applications based on chemical and materials sciences. However, common aminations techniques for lignin usually involve toxic chemicals and generate hindered and low reactivity amines.

In this study, we developed two new, simple, and benign 2-step methodologies for the elaboration of lignin-based polyamines from different technical lignins (kraft, soda and organosolv) with a selectivity towards reactive primary amines. These methods involve grafting amide groups onto lignin followed by a hydrolysis step. Non-toxic heterocyclic compounds N-acetyl-2-oxazolidinone and 2-methyl-2-oxazoline were used as amidation agents. Hydrolysis was performed in acetone-water mixtures. Reactions were studied on model compounds and optimized on lignins. Aminated lignins were fully characterized and primary amines were quantified using quantitative ¹⁹F NMR.

Our methods generated aminated lignins with low apparent molar masses and high solubility in water and solvents. Nitrogen contents of the products ranged between 2.0 and 3.5 mmol/g with reactive primary amines counts up to 1.7 mmol/g. These soluble and reactive lignin-based polyamines offer great potential as a replacement for fossil-based polyamines in e.g., the synthesis of aromatic polymer materials or as potential chelating, antibacterial agents.

The synthesis of housanes from cyclopropenes via highly strained intramolecular cyclopropanation is described. The reaction proceeds in synthetically useful yields and diastereoselectivity. Moreover, the application to the synthesis of unnatural housane-containing terpenoids is disclosed.

Abstract

The synthesis of housane derivatives from cyclopropenes is described. Under rhodium(II) catalysis, cyclopropenylvinyl carbinols can regioselectively generate a carbene intermediate which undergoes an intramolecular cyclopropanation to form a housane, a skeleton with similar ring strain as the cyclopropene precursor. The procedure shows a remarkable broad scope and efficiency. Moreover, the method served to prepare man-made housane-containing terpene derivatives, which are not accessible by Nature.

Electrosynthesis meets Simulation! A streamlined approach for producing hydrofuroin, a jet-fuel precursor, from biomass-derived furfural, is described, utilizing laser-structured Pb catalysts. Negligible impact of impurities highlights the catalyst's robustness. Integrating electrochemical approach and molecular dynamic simulations comprehended the reaction mechanisms, enhancing understanding of the hydrofuroin electrosynthesis.

Abstract

This research investigates the impact of laser-structuring of lead electrodes on the selectivity and production rate of hydrofuroin, a valuable jet fuel precursor derived from furfural (FF). Laser structuring of electrodes led to a slight enhancement in hydrofuroin selectivity, along with an improved production rate, suggesting promising advancements in electrosynthesis methodologies. The addition of acetic acid as an impurity did not significantly affect the selectivity or the production rate. This finding indicates that the catalytic activity of the electrode surface was not diminished by this impurity. Analysis via high-performance liquid chromatography revealed the presence of two isomers of hydrofuroin, indicating a complex reaction pathway. Combined experimental and molecular dynamics simulations indicated inner sphere adsorption of FF and H⁺ ions and outer sphere dimerization reaction to form hydrofuroin. These findings offer insights into surface morphology, adsorption, and reaction pathways, guiding future optimization of catalytic systems for sustainable chemical synthesis.

A general palladium-catalyzed hydroaminocarbonylation of acetylene towards important acrylamide derivatives is presented. The novel synthetic protocol shows high functional group-compatibility, high atom efficiency and good chemoselectivity to obtain a variety of bio-active compounds including several actual drugs.

Abstract

The development of all kinds of covalent drugs had a major impact on the improvement of the human health system. Covalent binding to target proteins is achieved by so-called electrophilic warheads, which are incorporated in the respective drug molecule. In the last decade, specifically acrylamides emerged as attractive warheads in covalent drug design. Herein, a straightforward palladium-catalyzed hydroaminocarbonylation of acetylene has been developed, allowing a modular and diverse synthesis of bio-active acrylamides. This general protocol features high atom efficiency, wide functional group compatibility, high chemoselectivity and proceeds additive free under mild reaction conditions. The synthetic utility of this protocol is showcased in the synthesis of ibrutinib, osimertinib, and other bio-active compound derivatives.

The novel designed bifunctional chiral electrocatalyst has been presented for the asymmetric electrochemical α-alkylation of aldehydes. The new bifunctional catalyst, which combines a chiral aminocatalyst with a redox mediator, significantly enhances efficiencies and stereoselectivities compared to conventional catalysts. It plays a dual role as a redox mediator for electrooxidation while simultaneously providing remarkable asymmetric induction for the stereoselective α-alkylation of aldehydes.

Abstract

Herein, we describe an innovative approach to the asymmetric electrochemical α-alkylation of aldehydes facilitated by a newly designed bifunctional chiral electrocatalyst. The highly efficient bifunctional chiral electrocatalyst combines a chiral aminocatalyst with a redox mediator. It plays a dual role as a redox mediator for electrooxidation, while simultaneously providing remarkable asymmetric induction for the stereoselective α-alkylation of aldehydes. Additionally, this novel catalyst exhibits enhanced catalytic activity and excellent stereoselective control comparable to conventional catalytic systems. As a result, this strategy provides a new avenue for versatile asymmetric electrochemistry. The electrooxidation of diverse phenols enables the C−H/C−H oxidative α-alkylation of aldehydes in a highly chemo- and stereoselective fashion. Detailed mechanistic studies by control experiments and cyclic voltammetry analysis demonstrate possible reaction pathways and the origin of enantio-induction.

An asymmetric paired electrolysis strategy for alkylation of sulfonylimines is reported. Anodic oxidation for benzylic radical formation and Lewis acid-catalyzed sulfonylimine reduction on the cathode are seamlessly cross-coupled using this protocol, providing enantio-enriched chiral amines containing a tetrasubstituted carbon stereocenter with high enantioselectivity under mild conditions.

Abstract

Enantioselective transformation of ubiquitous C(sp³)−H bonds into three-dimensional chiral scaffolds is of longstanding interest to synthetic chemists. Herein, an asymmetric paired electrolysis enables a highly efficient and sustainable approach to the enantioselective alkylation of sulfonylimines via C(sp³)−H functionalization. In this protocol, anodic oxidation for benzylic radical formation and Lewis acid-catalyzed sulfonylimine reduction on the cathode were seamlessly cross-coupled (up to 88 % yield). Enantioenriched chiral amines containing a tetrasubstituted carbon stereocenter are accessed with high enantioselectivity (up to 96 % ee). Mechanistic studies suggest that the amine generated in situ could serve as a base to deprotonate phenols and decrease the oxidation potential of the reaction, allowing phenols with lower potentials to be preferentially oxidized.

A system comprehensively analyzed the pertinent aspects of transition metal catalyzed promotion of the electrocatalytic reduction reaction of HMF, including catalytic mechanisms, in-situ characterization, catalyst design, and discussed the effects of catalyst design on catalytic activity from the perspectives of crystal facet effects, single-atom active sites, crystal defects, heterogeneous interfaces, and more.

Abstract

The electrochemical reduction reaction (HMFRR) of 5-hydroxymethylfurfural (HMF) has emerged as a promising avenue for the utilization and refinement of the biomass-derived platform molecule HMF into high-value chemicals, addressing energy sustainability challenges. Transition metal electrocatalysts (TMCs) have recently garnered attention as promising candidates for catalyzing HMFRR, capitalizing on the presence of vacant d orbitals and unpaired d electrons. TMCs play a pivotal role in facilitating the generation of intermediates through interactions with HMF, thereby lowering the activation energy of intricate reactions and significantly augmenting the catalytic reaction rate. In the absence of comprehensive and guiding reviews in this domain, this paper aims to comprehensively summarize the key advancements in the design of transition metal catalysts for HMFRR. It elucidates the mechanisms and pH dependency of various products generated during the electrochemical reduction of HMF, with a specific emphasis on the bond-cleavage angle. Additionally, it offers a detailed introduction to typical in-situ characterization techniques. Finally, the review explores engineering strategies and principles to enhance HMFRR activity using TMCs, particularly focusing on multiphase interface control, crystal face control, and defect engineering control. This review introduces novel concepts to guide the design of HMFRR electrocatalysts, especially TMCs, thus promoting advancements in biomass conversion.

For the first time, “cathodic hydrogenolysis of C _β −O−4 linkage” and “anodic C−H/N−H cross-coupling reaction” are paired in an undivided cell, thus the lignin (models) depolymerization and the synthesis of valuable triarylamine derivatives could be simultaneously achieved in a selective and energy-effective manner.

Abstract

The cleavage of C−O bonds is one of the most promising strategies for lignin-to-chemicals conversion, which has attracted considerable attention in recent years. However, current catalytic system capable of selectively breaking C−O bonds in lignin often requires a precious metal catalyst and/or harsh conditions such as high-pressure H₂ and elevated temperatures. Herein, we report a novel protocol of paired electrolysis to effectively cleave the C _β −O−4 bond of lignin model compounds and real lignin at room temperature and ambient pressure. For the first time, “cathodic hydrogenolysis of C _β −O−4 linkage” and “anodic C−H/N−H cross-coupling reaction” are paired in an undivided cell, thus the cleavage of C−O bonds and the synthesis of valuable triarylamine derivatives could be simultaneously achieved in an energy-effective manner. This protocol features mild reaction conditions, high atom economy, remarkable yield with excellent chemoselectivity, and feasibility for large-scale synthesis. Mechanistic studies indicate that indirect H* (chemical absorbed hydrogen) reduction instead of direct electron transfer might be the pathway for the cathodic hydrogenolysis of C _β −O−4 linkage.

Discover our innovative synthesis of 3-hydroxy-2-butanone (acetoin) from ethanol-derived acetaldehyde, a key step in producing C₄ molecules from bio-based resources. Using an N-heterocyclic carbene (NHC) catalyst, this process offers efficient C−C bond formation with high selectivity and robust performance. Explore catalyst immobilization, recycling, continuous flow experiments, and deactivation insights from advanced NMR spectroscopy.

Abstract

We report the catalytic synthesis of 3-hydroxy-2-butanon (acetoin) from acetaldehyde as a key step in the synthesis of C₄-molecules from ethanol. Facile C−C bond formation at the α-carbon of the C₂ building block is achieved using an N-heterocyclic carbene (NHC) catalyst. The immobilization of the catalyst on a Merrifield’s peptide resin and its spectroscopic characterisation using solid-state Nuclear Magnetic Resonance (NMR) is described herein. The immobilization of the NHC catalyst allows for process intensification steps and the reported catalytic system was subjected to batch recycling as well as continuous flow experiments. The robustness of the catalytic system was shown over a maximum of 10 h time-on-stream. Overall, high selectivity S>90 % was observed. The observed deactivation of the catalyst with increasing time-on-stream is explained by ex-situ ¹H solution-state, as well as ¹³C and ¹⁵N solid-state NMR spectra allowing us to develop a deeper understanding of the underlying decomposition mechanism of the catalyst.

The two-electron reduction to low-valent rhodium −I is underpinned by structural rearrangements that defines whether the redox transitions are stepwise or in a bielectronic fashion. Study of a parametrized series of Rh bis(diphosphine) complexes identifies how ligand parameters influence this behaviour, whereas an expedient computed electronic parameter allows correlating electronics and geometrics with redox potentials.

Abstract

Rhodium complexes in the −I and 0 oxidation states are of great potential interest in catalytic applications. In contrast to their rhodium +I congeners, however, the structural and electronic parameters governing their access and stability are far less understood. Herein, we investigate the two-electron reduction of a parameterized series of bis(diphosphine) Rh complexes [Rh(dxpy)₂]NTf₂ (x=P-substituent, y=alkanediyl bridging P atoms). Through (electro)reductions from the Rh^I parents, Rh^−I d ¹⁰-complexes were obtained and characterized spectroscopically, including ¹⁰³Rh NMR data. The reductive steps convolute with structural rearrangements from square planar to tetrahedral coordination. We found that the extent of these reorganisations defines whether the first E ⁰ (Rh^I/0) and second E ⁰ (Rh^0/−I) reduction potentials are normally ordered, leading to monoelectronic stepwise transitions, or inverted, giving bielectronic events. Reductionist approaches based on Hammett parameters or the P−Rh-P bite angles provide only partial correlations with the redox potentials. However, we identified the C−O stretch of analogue diphosphine complexes as an expedient computational parameter that enables these correlations through both electronic and geometric features, even in a predictive manner. Gaining control over two-electron reduction behaviors through rationalized ligand effects has potential impact beyond Rh complexes, for molecular and enzymatic metal sites commonly exhibiting bielectronic transitions.

By purely thermolytic treatment of different industrially produced lignins in highly concentrated aqueous KOH either vanillic acid or protocatechuic acid can be accessed in attractive yields and good selectivity. By employing a work-up of the reaction mixture with ion-exchange resins, the products could be obtained, and the media directly reused in further reactions.

Abstract

A new and practical method for the thermal degradation of technically relevant bio-based lignin is presented. By heating a solution of lignin in highly concentrated caustic potash, vanillic acid is almost exclusively obtained in yields up to 10.6 wt %. By altering the reaction parameters, the selectivity of the reaction can be shifted towards the demethylation product, protocatechuic acid, which is obtained in a yield of 6.9 wt %. Furthermore, the procedure was applicable to different types of Kraft and organosolv lignin. To create an economically feasible process, ion exchange resins were used for the work-up of the highly caustic reaction media without neutralizing the complete mixture. By the selective removal of the desired vanillic acid from the caustic potash, this alkaline media could directly be reused for at least 5 further lignin degradations without significant loss of yield.

“Whereas classical approaches focus only on cellulose… for upgrading biowaste directly to GVL, our research opens up the possibility of adding hemicellulose… to the substrate pool.” This and more about the story behind the research that inspired the Cover image is presented in the Cover Profile. Read the full text of the corresponding research at 10.1002/cssc.202301608. View the Front Cover 10.1002/cssc.20202400950.

Abstract

Invited for this issue's cover is the group of Martin Nielsen at the Technical University of Denmark. The image shows the chemical components of lignocellulose and the transformation of hemicellulose to GVL via furfural. The Research Article itself is available at 10.1002/cssc.202301608.

Within the core of circular economy, cigarette butts and their components (paper, filter and tobacco) were converted into Fe-N_x-C electrocatalysts for oxygen reduction reaction, via pyrolysis, KOH activation and blending with FePc precursor. The final electrocatalysts were tested in acid and alkaline media with RRDE after characterizing them from the morphological and chemical point of view.

Abstract

Trillion of cigarette butts are annually littered without being recycled. This work aims at valorizing the whole cigarette butts and their components (paper, filter and tobacco) into Fe-N_x-C electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The pristine wastes were pyrolyzed at 450 °C, activated with KOH at 700 °C, blended with iron phthalocyanine (FePc) precursor, and heat-treated at 600 °C to produce a robust Fe-N_x-C material with ORR active units. The effect of the cigarette components on the final electrocatalytic activity was evaluated by thoroughly investigating the surface chemistry with XPS. The electrocatalysts displayed similar results among the different components in both media due to comparable surface chemistry, especially concerning the nitrogen functional groups. The highest performance was obtained in alkaline where the electrocatalysts from whole cigarettes and paper (CIGF_450 and CIGPF_450) showed an E_1/2 of 0.89 V vs RHE, slightly larger than that of Pt/C with 40 wt % of Pt, which encouraged to replace Pt-based electrocatalysts in alkaline fuel cells.

The ion-pair [Ph₃C]⁺[B(C₆F₅)₄]⁻-mediated electrocatalytic benzylic C−H oxidation is described. In the absence of expensive oxidants and external supporting electrolyte, the selective oxidation of benzylic C−H bonds in air was achieved.

Abstract

The selective oxidation of benzylic C−H bonds is a pivotal transformation in organic synthesis. Undoubtedly, achieving efficient and highly selective aerobic oxidation of methylarenes to benzaldehydes has been highly challenging due to the propensity of benzaldehyde to undergo overoxidation under typical aerobic conditions. Herein, we propose an innovative approach to address this issue by leveraging electrocatalytic processes, facilitated by ion-pair mediators [Ph₃C]⁺[B(C₆F₅)₄]⁻. By harnessing the power of electrochemistry, we successfully demonstrated the effectiveness of our strategy, which enables the selective oxidation of benzylic C−H bonds in benzylic molecules and toluene derivatives. Notably, our approach exhibited high efficiency, excellent selectivity, and compatibility with various functional groups, underscoring the broad applicability of our methodology.

Nature Communications, Published online: 04 April 2024; doi:10.1038/s41467-024-47220-9