Homogeneous Catalysts Research Articles

Impact of a homogeneous hydrogen bond catalysis for the ethyl (hetero)arylidene cyanoacetate preparation in the presence of TMDP

Impact of a homogeneous hydrogen bond catalysis for the ethyl (hetero)arylidene cyanoacetate preparation in the presence of TMDP

The Feasibility of Using Electrostatic Interactions for Immobilizing Ru-bda Catalysts in Covalent Organic Framework: A Proof-of-Concept.

Heterogenization of molecular catalysts effectively resolves the separation issues of homogeneous catalysts and expands their application scenarios. In recent years, more and more studies have been using non-covalent interactions to achieve the heterogenization of molecular catalysts. Herein, electrostatic attraction was used to immobilize molecular catalysts, Ru-bda small molecular catalysts in COF materials, where the charged Ru-bda catalysts were immobilized in the oppositely charged COF with a high [Ru] loading content of ~0.2 mmol [Ru] g-1 COF. The leakage experiment verified that the immobilization of Ru-bda catalysts in COF by electrostatic interactions is stable in 0.1 M HClO4 and less than 5 % of molecular Ru-bda catalysts were leached into the solution in 2 hours. The chemical water oxidation experiment was conducted as a model catalysis reaction to verify the feasibility of using electrostatic interactions for immobilizing Ru-bda catalysts in COFs. The prepared Ru(bda)@COFs demonstrate a high catalytic activity of 268 μmol L-1 s-1 O2 for chemical water oxidation, illustrating the electrostatic attractions between COF and small molecules that can be used to immobilize homogeneous catalysts in heterogeneous materials. However, the robustness of COF material itself under catalytic conditions should be considered in practical applications.

Tailoring of Novel Ru (III) and Cr (III) Salen Complexes as Catalysts for a Sustainable and Green Synthesis of Dihydro‐tetrazolo [1,5‐a] thiazolo [4,5‐d] pyrimidin‐6‐yl morpholine: Experimental and Theoretical Approaches

ABSTRACTTwo novel Cr (III) and Ru (III) salen complexes based on {3,4‐Bis‐[(5‐chloro‐2‐hydroxy‐benzylidene)‐amino]‐phenyl}‐phenyl‐methanone ligand (CSAB) were synthesized. The complexes were characterized using various spectral and analytical methods. The catalytic performance of the CSAB complexes was investigated via a four‐component condensation reaction involving aromatic aldehydes, rhodamine, morpholine, and 5‐aminotetrazole under mild, environmentally friendly conditions. Different Lewis acids, bases, ionic liquid catalysts, solvents, and catalyst amounts were assessed to optimize the reaction parameters. Both catalyst systems demonstrated robust catalytic activity under strictly managed conditions, with the heterogeneous catalyst CSAB‐Ru showing superior efficacy compared to the homogeneous CSAB‐Cr catalyst. The study confirmed the catalytic capabilities of both complexes and evaluated their recyclability and reusability. The heterogeneous catalyst (CSAB‐Ru) could be reused seven times, whereas the homogeneous catalyst (CSAB‐Cr) could be recycled four times. Both complexes demonstrated strong catalytic activity and selectivity, resulting in high product yields. The study provides insights into the synthetic applications of novel CSAB complexes, highlighting their potential in organic transformations. It emphasizes their ease of use, safety, stability, component availability, quick reaction times, and high yields, making them promising for future industrial applications.

Conversion of Penta‐Acetyl‐Xylitol to 3‐Acetoxymethylene‐Tetrahydrofuran by a Combined Hetero‐/Homogeneous Tandem Catalyst System

A tandem catalyst system comprised of trifluoromethanesulfonic (triflic acid, HOTf) or Hafnium tetratriflate (Hf(OTf)4) and Ru/C in glacial acetic acid (HOAc) as the solvent at 200 °C and ~ 7 MPa hydrogen pressure in a batch reactor converts penta‐acetyl‐xylitol ((2R,3R,4S)‐Pentane‐1,2,3,4,5‐penta‐acetoxy‐pentane) or unprotected xylitol to 3‐acetoxymethylene‐tetrahydrofuran (3‐AMT) in up to 15 % yield at full conversion. A comparative analysis by SEM‐EDS and XPS of the fresh commercial Ru/C catalyst vs catalyst reused and recovered after 5 cycles shows increasing aggregation of ruthenium to larger particles with a concomitant decrease in yield of 3‐AMT to 8‐9 % for cycles 4 and 5. 3‐AMT or its hydrolysis product 3‐hydroxymethyl‐tetrahydrofuran (3‐HMT) are valuable synthons for the preparation of agrochemicals, pharmaceuticals and specialty polyurethanes and polyesters.

Tailoring rhodium-based metal-organic layers for parahydrogen-induced polarization: achieving 20% polarization of 1H in liquid phase

Abstract Heterogeneous catalysts for parahydrogen-induced polarization (HET-PHIP) would be useful for producing high sensitivity contrasting agents for magnetic resonance imaging (MRI) in liquid phase, as they can be removed by simple filtration. Although homogeneous hydrogenation catalysts are highly efficient for PHIP, their sensitivity decreases when anchored on porous supports due to slow substrate diffusion to the active sites and rapid depolarization within the channels. To address this challenge, we explored two-dimensional (2D) metal-organic layers (MOLs) as supports for active Rh complexes with diverse phosphine ligands and tunable hydrogenation activities, taking advantage of accessible active sites and chemical adaptability of the MOLs. By adjusting the electronic properties of phosphines, TPP-MOL-Rh-dppb (TPP = tris(4-carboxylphenyl)phosphine), featuring a κ2-connected di(phosphine) ligand, generated hyperpolarized styrene achieving over 2400-fold signal enhancement and polarization level of 20% for 1H in methanol-d4 solution. The TPP-MOL-Rh-dppb effectively inherited the high efficiency and pairwise addition of its homogenous catalyst while maintaining the heterogeneity of MOL. This work demonstrates the potential of 2D phosphine-functionalized MOLs as heterogenous solid support for HET-PHIP.

Acceptorless Dehydrogenation of Glycerol Catalysed by Ir(III) Complexes with Carbohydrate‐Functionalised Ligands: A Sweet Pathway to Produce Hydrogen and Lactic Acid

AbstractGlycerol, a by‐product of biodiesel production, has gained prominence as a precious platform chemical. To enhance the economic viability of the biodiesel production process and address the surplus of glycerol production, it is essential to transform it into value‐added products. In this context, homogeneous catalysis offers a promising avenue for glycerol valorisation. In this study, we introduce a family of iridium complexes bearing picolineamidate ligands with glucose‐functionalised substituents as novel homogeneous catalysts for glycerol to hydrogen and lactic acid conversion. These complexes exhibit high activity (conversion up to 53.3 %) and 99 % selectivity after 24 hours of reaction (TOFMAX=159 h−1, TON24h=2498). Notably, the reaction occurs under ambient air and at milder temperature conditions (120 °C) compared to other catalysts. These efforts in glycerol valorisation contribute to reducing biodiesel production costs, increasing the competitiveness of biofuels against petroleum‐based liquid fuels, giving rise to H2, through a global process with negative carbon dioxide emission, and lactic acid utilizable, among other, as a monomer for the synthesis of biodegradable plastics.

Catalytically Active Site Mapping Realized through Energy Transfer Modeling

AbstractThe demands of a sustainable chemical industry are a driving force for the development of heterogeneous catalytic platforms exhibiting facile catalyst recovery, recycling, and resilience to diverse reaction conditions. Homogeneous‐to‐heterogeneous catalyst transitions can be realized through the integration of efficient homogeneous catalysts within porous matrices. Herein, we offer a versatile approach to understanding how guest distribution and evolution impact the catalytic performance of heterogeneous host–guest catalytic platforms by implementing the resonance energy transfer (RET) concept using fluorescent model systems mimicking the steric constraints of targeted catalysts. Using the RET‐based methodology, we mapped condition‐dependent guest (re)distribution within a porous support on the example of modular matrices such as metal–organic frameworks (MOFs). Furthermore, we correlate RET results performed on the model systems with the catalytic performance of two MOF‐encapsulated catalysts used to promote CO2 hydrogenation and ring‐closing metathesis. Guests are incorporated using aperture‐opening encapsulation, and catalyst redistribution is not observed under practical reaction conditions, showcasing a pathway to advance catalyst recyclability in the case of host–guest platforms. These studies represent the first generalizable approach for mapping the guest distribution in heterogeneous host–guest catalytic systems, providing a foundation for predicting and tailoring the performance of catalysts integrated into various porous supports.

ZnO with Different Morphologies Sensitized by Metalloporphyrins as Catalysts for H2 Production by Water Splitting Under Sunlight.

In this work, zinc oxide with different morphologies and textural properties were prepared and sensitized with metalloporphyrins (MPs) aiming to improve its solar energy harvesting capability for H2 production by water splitting under sunlight (a 300 W Xe/Hg lamp). An anionic iron(III)porphyrin and a cationic manganese(III)porphyrin were immobilized on different ZnO solids predominantly by electrostatic interactions. In general, the prepared MP-free ZnO solid yielded modest catalytic results which had apparently no direct correlation with their textural properties or morphology. On the other hand, when these ZnO solids had iron or manganese porphyrin sensitizing them, their catalytic performances changed and a superior yield towards H2 production was observed in comparison to the pure ZnO solids, making evident the synergy achieved between these two components (ZnO and metalloporphyrins) for the prepared solids. It was also observed that the metalloporphyrins and the respective free-base ligand suffered redox reactions when used as homogenous catalyst in this reaction, which could influence their performances as catalysts. The same was not observed in the solids containing immobilized MP, suggesting some protective effect of the ZnO solids on the MP complexes upon immobilization probably due to interaction of the complexes with the ZnO matrix.

Modulating the Aggregation States of a Pd6L4 Cage for Selectivity Flipping during the Stereo‐Divergent Semi‐Hydrogenation of Alkynes

An enzyme‐mimicking catalytic system has been established using a singular palladium‐based octahedral cage as the supramolecular reactor, deftly unlocking off‐on‐off selectivity in the semi‐hydrogenation of alkynes. Water serves as a critical regulator, modulating the catalyst states, reaction rates, and endpoints. The choice of solvent system influences the activity of host‐guest binding and the reaction types of homogeneous and heterogeneous catalysis, effectively modifying the reaction steps involved in the Z→E isomerization during the semi‐hydrogenation of alkynes. Kinetic and inhibition experiments indicate that the catalyst mimics the binding and activation characteristics of enzymes towards substrates, enabling selective transformations within the confined enzyme‐mimicking environment. The utility of this switchable cage‐confined catalysis has been demonstrated in the synthesis and modification of complex biologically active molecules with controllable E/Z selectivity. This work sheds light on the design and control of artificial supramolecular counterparts of enzymes, offering fundamental insights into the factors influencing the activity and catalytic selectivity of biological macromolecules.

Modulating the Aggregation States of a Pd6L4 Cage for Selectivity Flipping during the Stereo-Divergent Semi-Hydrogenation of Alkynes.

An enzyme-mimicking catalytic system has been established using a singular palladium-based octahedral cage as the supramolecular reactor, deftly unlocking off-on-off selectivity in the semi-hydrogenation of alkynes. Water serves as a critical regulator, modulating the catalyst states, reaction rates, and endpoints. The choice of solvent system influences the activity of host-guest binding and the reaction types of homogeneous and heterogeneous catalysis, effectively modifying the reaction steps involved in the Z→E isomerization during the semi-hydrogenation of alkynes. Kinetic and inhibition experiments indicate that the catalyst mimics the binding and activation characteristics of enzymes towards substrates, enabling selective transformations within the confined enzyme-mimicking environment. The utility of this switchable cage-confined catalysis has been demonstrated in the synthesis and modification of complex biologically active molecules with controllable E/Z selectivity. This work sheds light on the design and control of artificial supramolecular counterparts of enzymes, offering fundamental insights into the factors influencing the activity and catalytic selectivity of biological macromolecules.

Sustainable Hydrogen Production by Glycerol and Monosaccharides Catalytic Acceptorless Dehydrogenation (AD) in Homogeneous Phase.

In the quest for sustainable hydrogen production, the use of biomass-derived feedstock is gaining importance. Acceptorless Dehydrogenation (AD) in the presence of efficient and selective catalysts has been explored worldwide as a suitable method to produce hydrogen from hydrogen-rich simple organic molecules. Among these, glycerol and sugars have the advantage of being cheap, abundant, and obtainable from fatty acid basic hydrolysis (biodiesel industry) and from biomass by biochemical and thermochemical processing, respectively. Although heterogeneous catalysts are more widely used for hydrogen production from biomass-based feedstock, the harsh reaction conditions applied limit applicability due to deactivation of active sites due to coking of carbonaceous materials. Moreover, heterogeneous catalyst are more difficult to fine-tune than homogeneous counterparts, and the latter also allow for high process selectivities under milder conditions. The present Concept article summarizes the main features of the most active homogeneous catalysts reported for glycerol and monosaccharides AD. In order to directly compare hydrogen production efficiencies, the choice of literature works was limited to reports where hydrogen was clearly quantified by yields and turnover numbers (TONs). The types of transition metals and ligands is discussed, together with a perspective view on future challenges of homogeneous AD reactions for practical applications.

Molecular complex inspired design of an efficient copper(II)-containing robust porous polymers for electrochemical water oxidation

Homogeneous copper-bipyridine complexes have been reported as effective catalysts for water oxidation, demonstrating significant potential as alternatives to precious metal-based complexes. However, these complexes face long-term stability and product separation challenges similar to many homogeneous catalysts. Meanwhile, recent studies have underscored the potential of metalated polymer networks, which integrate the structural advantages of polymers with the functional benefits of metal species, making them highly attractive for various applications. Herein, we integrated copper-bipyridine units into porous polymer networks to overcome the limitations of copper-bipyridine complexes. We prepared a series of copper-incorporated polymers (TpBpy-Cux) for electrochemical water oxidation. The electrochemical properties of these polymers were tuned by varying the copper content, with TpBpy-Cu3 presenting the best performance among the samples studied. TpBpy-Cu3 demonstrated a low Tafel slope of 69 mV/decade, achieved a high Faradaic efficiency (FE) of 94 %, and exhibited exceptional stability over 1000 cyclic scans. This study offers insights into the design and optimization of metal-incorporated porous polymer networks building on the foundational understanding of their molecular counterparts for advanced catalytic applications.

Synthesis, Structure and Catalytic Properties of Hyp3[Ge9Rh]PPh3

In single‐site homogeneous catalysts (SSHoCs) transition metal atoms are incorporated in the surface of a small homoatomic atom cluster. Within this concept the main group element cluster is considered as innocent support material, while the catalysis itself is realised at the transition metal atom. In the case of [Ge9] clusters, both transition metal atoms and the Ge atoms have low oxidation state. Thus improving the synthesis towards transition metal decorated Zintl cluster has become important in the last years, and the catalytic activity of these clusters is of high interest. An optimised one‐step synthetic protocol for Hyp3[Ge9Rh]PPh3 is presented. The product is characterised by NMR spectroscopy, LIFDI/MS and single crystal structure determination. The Rh atom is incorporated in the clusters surface and bridges a deltahedral cluster face, whereby one of the triangular edge opens forming an almost planar face of three Ge and one Rh atom. PPh3 ligand dissociation as well as the catalytic activity in the isomerisation of 1‐hexene and allylbenzene as well as the hydrogenation of those substrates with hydrogen is investigated.

A facile and green procedure in preparing dibenzo-chromeno-phenazine-diones using an effectual and recyclable Brønsted acidic ionic liquid

First, a Brønsted acid ionic liquid (BAIL) in the role of a double acid-base called 1,3-n-propyl-bipyridinium bisulfonic acid-ditrifluoroacetate (PBPBSDT) was produced, and its skeleton was determined via TGA, mass, 13C NMR, 19F NMR, 1H NMR and FT-IR data. Further, it was successfully applied in the preparation of dibenzo-chromeno-phenazine-dione derivatives (1a-12a, 9–15 min, 90–98%) via one-pot multicomponent domino reaction among 2 mmol 2-hydroxynaphthalene-1,4-dione, 1 mmol benzene-1,2-diamine, and 1 mmol aldehydes under optimal conditions (5 mol% of PBPBSDT, solvent-free, 60 °C). The proper reproducibility of the PBPBSDT homogeneous catalyst (5 times), solvent-free medium, reasonable TON (Turnover Number) and TOF (Turnover Frequency) numbers, the non-metallic framework of the catalyst, and the formation of C-N, C = N, C-C, C = C, C-O bonds in a single operation are the distinct advantages of this protocol.

Transition Metal Catalyzed Deuteration via Hydrogen Isotope Exchange

Direct hydrogen isotope exchange represents a distinctive strategy for deuterium labelling, where the protium is directly replaced by deuterium. In this graphic review, we summarized the progress in deuteration via transition metal catalyzed hydrogen isotope exchange. The review was organized according to the mechanism of C-H bond activation in the homogeneous catalysis, and the heterogeneous catalysis was also discussed according to the catalyst type. Representative mechanistic processes were depicted, and proven cases for tritiation were also highlighted.

Recent Advances in Immobilizing and Benchmarking Molecular Catalysts for Artificial Photosynthesis.

Transition metal complexes have been widely used as catalysts or chromophores in artificial photosynthesis. Traditionally, they are employed in homogeneous settings. Despite their functional versatility and structural tunability, broad industrial applications of these catalysts are impeded by the limitations of homogeneous catalysis such as poor catalyst recyclability, solvent constraints (mostly organic solvents), and catalyst durability. Over the past few decades, researchers have developed various methods for molecular catalyst heterogenization to overcome these limitations. In this review, we summarize recent developments in heterogenization strategies, with a focus on describing methods employed in the heterogenization process and their effects on catalytic performances. Alongside the in-depth discussion of heterogenization strategies, this review aims to provide a concise overview of the key metrics associated with heterogenized systems. We hope this review will aid researchers who are new to this research field in gaining a better understanding.

Lithium iodide promoted CO2 hydrogenation towards ethanol via biphasic lewis-acid-base pairs synergistic catalysis

Ethanol synthesis via CO2 hydrogenation is of great importance in view of its high-value utilization. Herein, combining with heterogeneous and homogenous catalysis, we have developed an efficient biphasic Lewis-acid-base pairs synergistic catalysis strategy from CO2 hydrogenation. Apart from conventional heterogeneous ethanol synthesis route, it was surprisingly found that LiI homogenous promoter significantly enhanced CO2 conversion, ethanol selectivity, and productivity. LiI promoted CO2 dissolution in pure water and accelerated reaction intermediates consumption, favoring CO2 conversion. In detail, it can weaken C-O bond of CH3OH intermediate through Li+-I- Lewis-acid-base catalysis. The formed CH3I* with lower bond energy for C-I was more facile to dissociate into CH3*, favoring its subsequent coupling with CO* to form ethanol. In combination of Rh1/CeTiOx catalyst, LiI promoter, and methanol as solvent, a record-breaking ethanol yield was achieved (223.1 mmol·g−1·h−1). The obtained ethanol yield was about 18.7 times of that reported the best result in literatures. Especially, the established catalyst system could also be applied for synthesis of higher-carbon-number alcohols by the CO2 hydrogenation with other alcohols solvent (CnH2n+1OH, n = 2,3…).

Advancing Hybrid Nanocatalyst Research: A Python-based Visualization of Similarity Analysis for Interdisciplinary and Sustainable Development

Background: This study presents a comprehensive analysis of hybrid nanocatalysts, which amalgamate attributes of both heterogeneous and homogeneous catalysts. Aim: To achieve a holistic understanding of the topic, we embarked on a meticulous exploration across multiple databases. Methods: The Web of Science repository yielded 239 pertinent documents, while the Scopus database offered a more exhaustive collection of 1,887 documents. Although Google Scholar suggested a staggering 25,000 articles, its unclear selection criteria raised questions about the precision and dependability of its data. Hence, our study primarily relied on the Scopus database to ensure an extensive sample and analytical rigor. Using the Python-boosted visualization of Similarities methodology, we illuminated interconnections among various terminologies, identifying burgeoning areas within hybrid nanocatalyst research. Results: Our findings emphasized the ascending trajectory toward innovating materials with superior properties in hybrid nanocatalysis. This trajectory accentuated the pivotal role of interdisciplinary collaboration and sustainable methodologies. Advanced analytical techniques, notably X-ray diffraction, emerged as quintessential in delineating the nuanced relationship between hybrid nanocatalysts' structural and functional attributes. We also spotlighted Energy-Dispersive X-ray Spectroscopy's capability in fine-tuning hybrid nanocatalysts' properties, enhancing their catalytic efficacy and selectivity. An intriguing trend our study unearthed was the surge in interest toward integrating natural enzymes as potential catalysts within hybrid nanocatalysts, positioning them as beacons for sustainable and cost-efficient catalyst development. Conclusion: By synthesizing these insights, this research underlines the significance of diverse characterization techniques and the ethos of interdisciplinary collaboration. The derived knowledge offers a repository for fellow researchers, guiding further inquiries, especially regarding integrating natural enzymes in hybrid nanocatalyst innovation.

Unraveling the synergistic mechanisms of dual-atom catalysts on BeN4 substrates for enhanced hydrogen evolution reaction: A machine learning-assisted first-principles study

Synergistic effects have been widely studied in both homogeneous and heterogeneous bimetallic catalysis. However, the exact mechanisms underlying the synergistic effects between bimetallic atoms remain elusive. This study, using density functional theory calculations, systematically explores a dual-atom catalyst (DAC) on a BeN4 substrate, where two beryllium atoms are substituted with transition metals. The results demonstrate that the dual-atom catalysis TMTM’@BeN4 exhibits synergistic effects. Notably, five DAC systems, particularly those co-doped with V and Cr, significantly reduce the Gibbs free energy (ΔGH∗) for the hydrogen evolution reaction (HER). We further utilized machine learning to explore how the dual-atom catalysts exhibit synergistic effects. Machine learning analysis indicates that changes in the average interatomic distance and the Fermi level of the catalyst system are the main factors influencing the Gibbs free energy variation in dual-atom catalysts, jointly determining the hydrogen evolution catalytic activity. This work provides profound insights into understanding the synergistic mechanisms of dual-atom catalysts.

Recent Advances in Homogeneous Catalysts for the Acceptorless Dehydrogenation of Alcohols to Ketones and Aldehydes

Recent Advances in Homogeneous Catalysts for the Acceptorless Dehydrogenation of Alcohols to Ketones and Aldehydes