Applied hydroformylation

Sustaining syngas production at a near-unity H2/CO ratio in the photo-induced dry reforming of methane independent of the reactant gas composition

A syngas was generated at a near-unity H2/CO ratio independent of the reactant gas composition over Rh-loaded strontium titanate in the photo-induced dry reforming of methane. Moreover, light irradiation inhibited side reactions, such as the reverse water gas shift reaction and the precipitation of the solid-state carbon. These results were not explained by thermodynamic equilibrium, but were presumably owing to the unique effect of the photogenerated electron-hole pairs.

Polyoxometalates Based Catalysts for Carbonylation Reactions: A Review

As a type of diverse and structurally adjustable metal-oxo clusters, polyoxometalates (POMs) based materials have been extensively applied as a catalysis in various valuable reactions. This review summarized recent progress in the application of POMs-based catalysts for various carbonylation reactions including (1). Carbonylation of olefins, (2). Carbonylation of formaldehyde, (3). Carbonylation of methanol or dimethyl ether, (4). Oxidative carbonylation of methane, (5). Oxidative carbonylation of phenol and (6). Reductive carbonylation of nitrobenzene. A brief perspective on POMs-based catalysts for the carbonylation reactions is proposed.

Polymerized ionic liquid Co-catalysts driving photocatalytic CO2 transformation

Photocatalytic production of CO from CO2 has the potential for safe and atom-economic production of feedstock chemicals via in situ carbonylation chemistry. We developed novel ionic liquid-based polymeric materials through radical copolymerisation of 1-butyl-3-vinylimidazolium chloride and photocatalytically active Re- and Ru-complexes that serve as the CO2 reduction catalyst and photosensitiser, respectively. The crosslinked polymeric framework allows for the facile immobilisation of molecular organometallic complexes for use as heterogenised catalysts; moreover, the involved imidazolium core units co-catalyze the reduction of CO2 via covalent interaction. The ratio of sensitiser and catalyst was analysed by laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) and set in relation to results from photocatalytic experiments. Ultimately, the heterogenous polymeric framework showed high selectivity for CO formation on photocatalytic CO2 reduction with improved stability to the corresponding homogenous system.

Enantioconvergent synthesis of axially chiral amides enabled by Pd-catalyzed dynamic kinetic asymmetric aminocarbonylation

Atropisomeric biaryls bearing carbonyl groups have attracted increasing attention due to their prevalence in diverse bioactive molecules and crucial role as efficient organo-catalysts or ligands in asymmetric transformations. However, their preparation often involves tedious multiple steps, and the direct synthesis via asymmetric carbonylation has scarcely been investigated. Herein, we report an efficient palladium-catalyzed enantioconvergent aminocarbonylation of racemic heterobiaryl triflates with amines via dynamic kinetic asymmetric transformation (DyKAT). This protocol features a broad substrate scope and excellent compatibility for rapid construction of axially chiral amides in good to high yields with excellent enantioselectivities. Detailed mechanistic investigations discover that the base can impede the intramolecular hydrogen bond-assisted axis rotation of the products, thus allowing for the success to achieve high enantioselectivity. Moreover, the achieved axially chiral heterobiaryl amides can be directly utilized as N,N,N-pincer ligands in copper-catalyzed enantioselective formation of C(sp3)-N and C(sp3)-P bonds.

Elucidation of hemilabile-coordination-induced tunable regioselectivity in single-site Rh-catalyzed heterogeneous hydroformylation

Revealing key factors that modulate the regioselectivity in heterogeneous hydroformylation requires identifying and monitoring the dynamic evolution of the truly active center under real reaction conditions. However, unambiguous in situ characterizations are still lacking. Herein, we elaborately construct a series of Rh-POPs catalysts for propylene hydroformylation which exhibited tunable regioselectivity. Multi-technique approaches reveal the unique microenvironment of the diverse HRh(CO)(PPh3-frame)2 sites with distinct P-Rh-P bite angles ranging from 90° to 120° and 158° to 168°, respectively. In situ time-resolved XAFS, FT-IR, and quasi-in situ Solid-state NMR experiments combined with DFT calculations explain the dynamic evolution of the electronic and coordinate state of the distinct active sites induced by hemilabile PPh3-frame ligands and further disclose the regulatory mechanism of regioselectivity. These state-of-the-art techniques and multiscale analysis advance the understanding of how hemilabile coordination influences regioselectivity and will provide a new thought to modulate the regioselectivity in future industrial processes.

Towards the Use of Renewable Syngas for the Decarbonization of Industry

In this article we analyze how syngas produced in a renewable way can replace fossil-fuel based syngas production and thereby play an essential role in the decarbonization of industry. We show that in essentially all industrial applications renewable H2 and/or CO can replace syngas from fossil fuel feedstocks, and quantify the flows of these chemical building blocks required for the transformation of industry towards a net-zero emitting sector. We also undertake a techno-economic analysis, in which we demonstrate that under specific assumptions for the learning rates of some of the key process components, renewable syngas can become cost-competitive with that produced from fossil fuels. Cost competitiveness, however, only materializes for four of the five routes when natural gas prices are at least around 3 €/GJ and carbon taxes increase from 90 €/tCO2 today to 300 €/tCO2 in 2050.

Understanding the role of supported Rh atoms and clusters during hydroformylation and CO hydrogenation reactions with in situ/operando XAS and DRIFT spectroscopy

Supported Rh single-atoms and clusters on CeO2, MgO, and ZrO2 were investigated as catalysts for hydroformylation of ethylene to propionaldehyde and CO hydrogenation to methanol/ethanol with in situ/operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray absorption spectroscopy (XAS). Under hydroformylation reaction conditions, operando spectroscopic investigations unravel the presence of both single atoms and clusters and detected at first propanal and then methanol. We find that the formation of methanol is associated with CO hydrogenation over Rh clusters which was further confirmed under CO hydrogenation conditions at elevated pressure. The activity of catalysts synthesized via a precipitation (PP) method over various supports towards the hydroformylation reaction follows the order: Rh/ZrO2 > Rh/CeO2 > Rh/MgO. Comparing Rh/CeO2 catalysts synthesized via different methods, catalysts prepared by flame spray pyrolysis (FSP) showed catalytic activity for the hydroformylation reaction at lower temperatures (413 K), whereas catalysts prepared by wet impregnation (WI) showed the highest stability. These results not only provide fundamental insights into the atomistic level of industrially relevant reactions but also pave the way for a rational design of new catalysts in the future.

Calix[2]azolium[2]benzimidazolone hosts for selective binding of neutral substrates in water

The separation and purification of chemical raw materials, particularly neutral compounds with similar physical and chemical properties, represents an ongoing challenge. In this study, we introduce a class of water-soluble macrocycle compound, calix[2]azolium[2]benzimidazolone (H), comprising two azolium and two benzimidazolone subunits. The heterocycle subunits form a hydrophobic binding pocket that enables H1 to encapsulate a series of neutral guests in water with 1:1 or 2:1 stoichiometry, including aldehydes, ketones, and nitrile compounds. The host-guest complexation in the solid state was further confirmed through X-ray crystallography. Remarkably, H1 was shown to be a nonporous adaptive crystal material to separate valeraldehyde from the mixture of valeraldehyde/2-methylbutanal/pentanol with high selectivity and recyclability in the solid states. This work not only demonstrates that azolium-based macrocycles are promising candidates for the encapsulation of organic molecules but also shows the potential application in separation science.

A Resorcin[4]arene-Based Phosphite-Phosphine Ligand for the Branched-Selective Hydroformylation of Alkyl Alkenes

Synthesis of a chelating phosphite-phosphine ligand from a tris(quinoxaline) extended resorcin[4]arene and its application in the rhodium-catalyzed hydroformylation of terminal alkyl alkenes are reported. Rhodium complexes are formed within the cavity of the macrocycle and branched-selective hydroformylation of 1-octene with a b/l ratio of 5.9 has been achieved at 60 °C under 1:1 H2/CO (20 bar).

Chemo-, regio- and enantioselective hydroformylation of trisubstituted cyclopropenes: access to chiral quaternary cyclopropanes

Catalytic asymmetric synthesis of polysubstituted chiral cyclopropane presents a significant challenge in organic synthesis due to the difficulty in enantioselective control. Here we report a rhodium-catalyzed highly chemo-, regio- and enantioselective hydroformylation of trisubstituted cyclopropenes affording chiral quaternary cyclopropanes. Importantly, the easy made sterically bulky ligand L1 can effectively suppress hydrogenation and decomposition reactions and give quaternary cyclopropanes with high regio- and enantioselectivities for both aryl and alkyl functionalized substrates. Control experiments and computational studies reveal the sterically hindered well-defined chiral pocket instead of the substrates bearing electron-withdrawing diester groups is important for controlling the enantioselectivity and regioselectivity. Scale-up reaction and follow-up diverse transformations are also presented. Density Functional theory (DFT) computations suggest that the regio- and enantio-selectivities originate from the cyclopropene insertion to the Rh-H bond. The high regioselectivity is found to benefit from the presence of more efficient noncovalent interactions (NCIs) manifesting in the form of C-H···Cl, C-H···N, and l.p(Cl)···π contacts.

Atomic-Level Asymmetric Tuning of the Co1-N3P1 Catalyst for Highly Efficient N-Alkylation of Amines with Alcohols

Despite the extensive development of non-noble metals for the N-alkylation of amines with alcohols, the exploitation of catalysts with high selectivity, activity, and stability still faces challenges. The controllable modification of single-atom sites through asymmetric coordination with a second heteroatom offers new opportunities for enhancing the intrinsic activity of transition metal single-atom catalysts. Here, we prepared the asymmetric N/P hybrid coordination of single-atom Co1-N3P1 by absorbing the Co-P complex on ZIF-8 using a concise impregnation-pyrolysis process. The catalyst exhibits ultrahigh activity and selectivity in the N-alkylation of aniline and benzyl alcohol, achieving a turnover number (TON) value of 3480 and a turnover frequency (TOF) value of 174-h. The TON value is 1 order of magnitude higher than the reported catalysts and even 37-fold higher than that of the homogeneous catalyst CoCl2(PPh3)2. Furthermore, the catalyst maintains its high activity and selectivity even after 6 cycles of usage. Controlling experiments and isotope labeling experiments confirm that in the asymmetric Co1-N3P1 system, the N-alkylation of aniline with benzyl alcohol proceeds via a transfer hydrogenation mechanism involving the monohydride route. Theoretical calculations prove that the superior activity of asymmetric Co1-N3P1 is attributed to the higher d-band energy level of Co sites, which leads to a more stable four-membered ring transition state and a lower reaction energy barrier compared to symmetrical Co1-N4.

Robust, scalable, and highly selective spirocyclic catalysts for industrial hydroformylation and isomerization-hydroformylation

Hydroformylation (HF) or isomerization-hydroformylation (ISO-HF) represents the most direct and practical route for producing aldehydes on an industrial scale. To resolve the issues of low activity, low linear/branched (l/b) ratio, and low stability in HF and ISO-HF, we herein reported a class of spirocyclic diphosphites. Notably, the ligand termed O-SDPhite afforded excellent catalytic activity and regioselectivity for the HF of various olefins. Excellent l/b ratio and an unprecedented turnover number of up to 17,620,000 were achieved. O-SDPhite was also found to be effective in the regioselective ISO-HF of the industrially related cheap and abundant C4 Raffinates to n-valeraldehyde produced on a multimillion-ton scale. The reaction with O-SDPhite, superior to that of benchmark Biphephos, was continuously operated for 41 days and afforded an average 38.6 l/b ratio (31 days and 14.7 l/b ratio for Biphephos).

Highly (regio)selective hydroformylation of olefins using self-assembling phosphines

New phosphines with self-assembling 6-pyridinone moities were prepared, characterized, and examined in the hydroformylation of diverse olefins. Testing various known and novel ligands in the presence of [Rh(acac)(CO)2] under industrially relevant conditions, the hydroformylation of 1-octene proceeds best with 6,6'-(phenylphosphanediyl)bis(pyridin-2(1H)-one) (DPONP). Control experiments and modelling studies indicate dimerization of this ligand at higher temperatures (>100 °C). The optimal catalyst system is able to conserve high product linearity (>90%) for a broad range of olefins at industrially-employed temperatures at low ligand loading.

Revisiting the Preparation and Catalytic Performance of a Phosphine-Modified Co(II) Hydroformylation Precatalyst

In light of recent conflicting reports regarding the hydroformylation catalytic activity derived from cationic Co(II) precatalysts of the form [Co(acac)(bis(phosphine))]BF4, the synthetic procedures and characterization of [Co(acac)(dppBz)]BF4, 1, are evaluated. Leveraging calibrated ESI-TOF MS methodologies, substantial quantities of Co(acac)2(dppBz), 2, were observed within samples of 1. The source of the impurity, 2, is determined to derive from incomplete protonolysis of the Co(acac)2 precursor and ligand scrambling occurring during the synthesis of 1. Revised synthetic procedures using lower temperature conditions and longer reaction times afford analytically pure samples of 1 based on ESI-TOF MS and NMR spectroscopic analysis. Complex 1 is demonstrated to act as a hydroformylation precatalyst for the conversion of 1-hexene to 1-heptanal under relatively mild conditions at 51.7 bar and 140 °C. The presence of impurity 2 is shown to dramatically decrease the catalytic performance derived from 1.

Metal-Organic Framework-Induced Rh Monocoodination on Diphosphine Ligand Enables Catalytic Hydroformylation of Aliphatic Olefins at Room Temperature and Pressure

Persistent challenges in hydroformylation of olefins include controlling regioselectivity, particularly for short aliphatic olefins and conducting reactions under ambient conditions. We report here the synthesis of monophosphine-Rh complexes on a typical chelated diphosphine ligand mediated by a Zr-MOF through isolating a pair of phosphorus atoms. We demonstrate that single-crystal X-ray diffraction can elucidate the structural transformation of the Rh catalyst during olefin hydroformylation, providing valuable information on active site reconstruction during catalysis. The Rh-MOF catalyst demonstrates excellent catalytic and recyclable performance in the hydroformylation of short aliphatic olefins with linear to branched ratios of up to 99 : 1. Due to the framework's capacity to adsorb and concentrate gases, the catalytic reactions occur under room temperature and pressure, eliminating the need for the high temperature and pressures typically required in homogeneous systems. This study show that Zr-MOF can be a unique platform for synthesizing unusual catalytic species that cannot exist in solutions for meaningful chemical transformations and elucidate valuable structural information pertaining to metal-based catalysis.

Merging High-Pressure Syngas Metal Catalysis and Biocatalysis in Tandem One-Pot Processes for the Synthesis of Nonchiral and Chiral Alcohols from Alkenes in Water

While simultaneously proceeding reactions are among the most fascinating features of biosynthesis, this concept of tandem processes also offers high potential in the chemical industry in terms of less waste production and improved process efficiency and sustainability. Although examples of one-pot chemoenzymatic syntheses exist, the combination of completely different reaction types is rare. Herein, we demonstrate that extreme "antipodes" of the "worlds of catalysis", such as syngas-based high-pressure hydroformylation and biocatalyzed reduction, can be combined within a tandem-type one-pot process in water. No significant deactivation was found for either the biocatalyst or the chemocatalyst. A proof-of-concept for the one-pot process starting from 1-octene was established with >99 % conversion and 80 % isolated yield of the desired alcohol isomers. All necessary components for hydroformylation and biocatalysis were added to the reactor from the beginning. This concept has been extended to the enantioselective synthesis of chiral products by conducting the hydroformylation of styrene and an enzymatic dynamic kinetic resolution in a tandem mode, leading to an excellent conversion of >99 % and an enantiomeric ratio of 91 : 9 for (S)-2-phenylpropanol. The overall process runs in water under mild and energy-saving conditions, without any need for intermediate isolation.

Recent developments in the synthesis and applications of terpyridine-based metal complexes: a systematic review

Terpyridine-based metal complexes have emerged as versatile and indispensable building blocks in the realm of modern chemistry, offering a plethora of applications spanning from materials science to catalysis and beyond. This comprehensive review article delves into the multifaceted world of terpyridine complexes, presenting an overview of their synthesis, structural diversity, and coordination chemistry principles. Focusing on their diverse functionalities, we explore their pivotal roles in catalysis, supramolecular chemistry, luminescent materials, and nanoscience. Furthermore, we highlight the burgeoning applications of terpyridine complexes in sustainable energy technologies, biomimetic systems, and medicinal chemistry, underscoring their remarkable adaptability to address pressing challenges in these fields. By elucidating the pivotal role of terpyridine complexes as versatile building blocks, this review provides valuable insights into their current state-of-the-art applications and future potential, thus inspiring continued innovation and exploration in this exciting area of research.

Diversification of Pharmaceutical Manufacturing Processes: Taking the Plunge into the Non-PGM Catalyst Pool

Recent global events have led to the cost of platinum group metals (PGMs) reaching unprecedented heights. Many chemical companies are therefore starting to seriously consider and evaluate if and where they can substitute PGMs for non-PGMs in their catalytic processes. This review covers recent highly relevant applications of non-PGM catalysts in the modern pharmaceutical industry. By highlighting these selected successful examples of non-PGM-catalyzed processes from the literature, we hope to emphasize the enormous potential of non-PGM catalysis and inspire further development within this field to enable this technology to progress toward manufacturing processes. We also present some historical contexts and review the perceived advantages and challenges of implementing non-PGM catalysts in the pharmaceutical manufacturing environment.

Microkinetic Molecular Volcano Plots for Enhanced Catalyst Selectivity and Activity Predictions

Molecular volcano plots, which facilitate the rapid prediction of the activity and selectivity of prospective catalysts, have emerged as powerful tools for computational catalysis. Here, we integrate microkinetic modeling into the volcano plot framework to develop "microkinetic molecular volcano plots". The resulting unified computational framework allows the influence of important reaction parameters, including temperature, reaction time, and concentration, to be quickly incorporated and more complex situations, such as off-cycle resting states and coupled catalytic cycles, to be tackled. Compared to previous generations of molecular volcanoes, these microkinetic counterparts offer a more comprehensive understanding of catalytic behavior, in which selectivity and product ratios can be explicitly determined by tracking the evolution of each product concentration over time. This is demonstrated by examining two case studies, rhodium-catalyzed hydroformylation and metal-catalyzed hydrosilylation, in which the unique insights provided by microkinetic modeling, as well as the ability to simultaneously screen catalysts and reaction conditions, are highlighted. To facilitate the construction of these plots/maps, we introduce mikimo, a Python program that seamlessly integrates with our previously developed automated volcano builder, volcanic.

Copper-catalyzed syn-hydroformylation of alkynes with silanes and N,N-dimethylformamide dimethylacetal

A copper-catalyzed syn-hydrocarbonization of internal alkynes with N,N-dimethylformamide dimethylacetal and silanes has been disclosed that offers an efficient and expedient access to (E)-α,β-unsaturated aldehydes. This highly selective process, which can be performed at gram-scale, enjoys operational simplicity, as well as syngas-free conditions.

Probing Basal and Prismatic Planes of Graphitic Materials for Metal Single Atom and Subnanometer Cluster Stabilization

Supported metal single atom catalysis is a dynamic research area in catalysis science combining the advantages of homogeneous and heterogeneous catalysis. Understanding the interactions between metal single atoms and the support constitutes a challenge facing the development of such catalysts, since these interactions are essential in optimizing the catalytic performance. For conventional carbon supports, two types of surfaces can contribute to single atom stabilization: the basal planes and the prismatic surface; both of which can be decorated by defects and surface oxygen groups. To date, most studies on carbon-supported single atom catalysts focused on nitrogen-doped carbons, which, unlike classic carbon materials, have a fairly well-defined chemical environment. Herein we report the synthesis, characterization and modeling of rhodium single atom catalysts supported on carbon materials presenting distinct concentrations of surface oxygen groups and basal/prismatic surface area. The influence of these parameters on the speciation of the Rh species, their coordination and ultimately on their catalytic performance in hydrogenation and hydroformylation reactions is analyzed. The results obtained show that catalysis itself is an interesting tool for the fine characterization of these materials, for which the detection of small quantities of metal clusters remains a challenge, even when combining several cutting-edge analytical methods.

Electrifying Hydroformylation Catalysts Exposes Voltage-Driven C-C Bond Formation

Electrochemical reactions can access a significant range of driving forces under operationally mild conditions and are thus envisioned to play a key role in decarbonizing chemical manufacturing. However, many reactions with well-established thermochemical precedents remain difficult to achieve electrochemically. For example, hydroformylation (thermo-HFN) is an industrially important reaction that couples olefins and carbon monoxide (CO) to make aldehydes. However, the electrochemical analogue of hydroformylation (electro-HFN), which uses protons and electrons instead of hydrogen gas, represents a complex C-C bond-forming reaction that is difficult to achieve at heterogeneous electrocatalysts. In this work, we import Rh-based thermo-HFN catalysts onto electrode surfaces to unlock electro-HFN reactivity. At mild conditions of room temperature and 5 bar CO, we achieve Faradaic efficiencies of up to 15% and turnover frequencies of up to 0.7 h-1. This electro-HFN rate is an order of magnitude greater than the corresponding thermo-HFN rate at the same catalyst, temperature, and pressure. Reaction kinetics and operando X-ray absorption spectroscopy provide evidence for an electro-HFN mechanism that involves distinct elementary steps relative to thermo-HFN. This work demonstrates a step-by-step experimental strategy for electrifying a well-studied thermochemical reaction to unveil a new electrocatalyst for a complex and underexplored electrochemical reaction.

CuH-Catalyzed Regio- and Enantioselective Formal Hydroformylation of Vinyl Arenes

A highly enantioselective formal hydroformylation of vinyl arenes enabled by copper hydride (CuH) catalysis is reported. Key to the success of the method was the use of the mild Lewis acid zinc triflate to promote the formation of oxocarbenium electrophiles through the activation of diethoxymethyl acetate. Using the newly developed protocol, a broad range of vinyl arene substrates underwent efficient hydroacetalization reactions to provide access to highly enantioenriched α-aryl acetal products in good yields with exclusively branched regioselectivity. The acetal products could be converted to the corresponding aldehydes, alcohols, and amines with full preservation of the enantiomeric purity. Density functional theory studies support that the key C-C bond-forming event between the alkyl copper intermediate and the oxocarbenium electrophile takes place with inversion of configuration of the Cu-C bond in a backside SE2-type mechanism.

A Tandem Hydroformylation-Organocatalyzed Friedel-Crafts Reaction for the Synthesis of Diindolylmethanes

Herein, we present an efficient and atom-economic tandem hydroformylation organocatalyzed Friedel-Crafts reaction sequence for the synthesis of diindolylmethanes. Classic syntheses have relied on (Lewis) acid activation of aldehydes, which are often not commercially available and rather sensitive in handling. In contrast, the combination of rhodium-catalyzed hydroformylation and subsequent organocatalytic activation of the in-situ formed aldehydes allows the use of readily available and stable alkenes with various functional groups while avoiding acidic conditions to expand the range of available diindolylmethanes. A broad scope of diindolylmethanes was prepared in yields up to 85 % demonstrates the utility of the presented method.

Probing Homogeneous Catalysts and Precatalysts in Solution by Exchange-Mediated Overhauser Dynamic Nuclear Polarization NMR

Triphenylphosphine (PPh3) is a ubiquitous ligand in organometallic chemistry that has been shown to give enhanced 31P NMR signals at high magnetic field via a scalar-dominated Overhauser effect dynamic nuclear polarization (OE DNP). However, PPh3 can only be polarized via DNP in the free form, while the coordinated form is DNP-inactive. Here, we demonstrate the possibility of enhancing the 31P NMR signals of coordinated PPh3 in metal complexes in solution at room temperature by combining Overhauser effect DNP and chemical exchange between the free and coordinated PPh3 forms. With this method, we successfully obtain 31P DNP enhancements of up to 2 orders of magnitude for the PPh3 ligands in Rh(I), Ru(II), Pd(II), and Pt(II) complexes, and we show that the DNP enhancements can be used to determine the activation energy of the ligand exchange reaction.

A Sustainable and Versatile Cellulose-based CO Surrogate for Carbonylative Reactions

The highly toxic and flammable nature of CO lead to high handling demand for its use and storage, undoubtedly constricting its further academic exploration for carbonylative reactions in laboratory. Although many CO surrogates have been developed and applied in carbonylative reactions instead of CO gas, exploration of more versatile CO surrogates for diverse carbonylations is still highly desirable. Here we report a cellulose-based CO surrogate (cellulose-CO), which prepared from cheap and abundant cellulose through a simple and green process. The very mild and efficient CO release makes this reagent a highly competitive candidate for providing CO in carbonylation. This surrogate is compatible with a wide variety of functional groups in various carbonylative reactions due to the excellent compatibility of cellulose-CO. Moreover, the cellulose-CO exhibits excellent chemical stability which can be stored exposed to air for 12 months, making this CO surrogate a robust and general reagent in CO chemistry.

Regioselective hydroformylation of propene catalysed by rhodium-zeolite

Hydroformylation is an industrial process for the production of aldehydes from alkenes1,2. Regioselective hydroformylation of propene to high-value n-butanal is particularly important, owing to a wide range of bulk applications of n-butanal in the manufacture of various necessities in human daily life3. Supported rhodium (Rh) hydroformylation catalysts, which often excel in catalyst recyclability, ease of separation and adaptability for continuous-flow processes, have been greatly exploited4. Nonetheless, they usually consist of rotationally flexible and sterically unconstrained Rh hydride dicarbonyl centres, only affording limited regioselectivity to n-butanal5-8. Here we show that proper encapsulation of Rh species comprising Rh(I)-gem-dicarbonyl centres within a MEL zeolite framework allows the breaking of the above model. The optimized catalyst exhibits more than 99% regioselectivity to n-butanal and more than 99% selectivity to aldehydes at a product formation turnover frequency (TOF) of 6,500 h-1, surpassing the performance of all heterogeneous and most homogeneous catalysts developed so far. Our comprehensive studies show that the zeolite framework can act as a scaffold to steer the reaction pathway of the intermediates confined in the space between the zeolite framework and Rh centres towards the exclusive formation of n-butanal.

Suppressing Metal Leaching and Sintering in Hydroformylation Reaction by Modulating the Coordination of Rh Single Atoms with Reactants

Hydroformylation reaction is one of the largest homogeneously catalyzed industrial processes yet suffers from difficulty and high cost in catalyst separation and recovery. Heterogeneous single-atom catalysts (SACs), on the other hand, have emerged as a promising alternative due to their high initial activity and reasonable regioselectivity. Nevertheless, the stability of SACs against metal aggregation and leaching during the reaction has rarely been addressed. Herein, we elucidate the mechanism of Rh aggregation and leaching by investigating the structural evolution of Rh1@silicalite-1 SAC in response to different adsorbates (CO, H2, alkene, and aldehydes) by using diffuse reflectance infrared Fourier transform spectroscopy, X-ray adsorption fine structure, and scanning transmission electron microscopy techniques and kinetic studies. It is discovered that the aggregation and leaching of Rh are induced by the strong adsorption of CO and aldehydes on Rh, as well as the reduction of Rh3+ by CO/H2 which weakens the binding of Rh with support. In contrast, alkene effectively counteracts this effect by the competitive adsorption on Rh atoms with CO/aldehyde, and the disintegration of Rh clusters. Based on these results, we propose a strategy to conduct the reaction under conditions of high alkene concentration, which proves to be able to stabilize Rh single atom against aggregation and/or leaching for more than 100 h time-on-stream.

Pd-catalysed synthesis of oxomalonamides through adjacent triple carbonylation of tertiary amines

The monocarbonylation and dicarbonylation reactions are well-established reactions in carbonylation chemistry. This work reports unusual oxidative adjacent triple carbonylation of the tertiary amine towards oxomalonamide synthesis using a Pd catalyst. The protocol involves the use of inert tertiary amines as an active reservoir of secondary amines through sp3 C-N bond activation using O2 as an ideal oxidant.

Co/SiO2 Catalyst for Methoxycarbonylation of Acetylene: On Catalytic Performance and Active Species

Reppe carbonylation of acetylene is an atom-economic and non-petroleum approach to synthesize acrylic acid and acrylate esters, which are key intermediates in the textile, leather finishing, and polymer industries. In the present work, a noble metal-free Co@SiO2 catalyst was prepared and evaluated in the methoxycarbonylation reaction of acetylene. It was discovered that pretreatment of the catalyst by different reductants (i.e., C2H2, CO, H2, and syngas) greatly improved the catalytic activity, of which Co/SiO2-H2 demonstrated the best performance under conditions of 160 °C, 0.05 MPa C2H2, 4 MPa CO, and 1 h, affording a production rate of 4.38 gMA+MP gcat-1 h-1 for methyl acrylate (MA) and methyl propionate (MP) and 0.91 gDMS gcat-1 h-1 for dimethyl succinate (DMS), respectively. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectra of CO adsorption (CO-DRIFTS) measurements revealed that an H2 reduction decreased the size of the Co nanoparticles and promoted the formation of hollow architectures, leading to an increase in the metal surface area and CO adsorption on the catalyst. The hot filtration experiment confirmed that Co2(CO)8 was generated in situ during the reaction or at the pre-activation stage, which served as the genuine active species. Our work provides a facile and convenient approach to the in situ synthetization of Co2(CO)8 for a Reppe carbonylation reaction.

Highly active and regioselective hydroaminomethylation of olefins catalyzed by Rh/sulfoxantphos with ZSM-5

Rh-catalyzed hydroaminomethylation has been developed with acid sulfoxantphos and ZSM-5. Linear amines were obtained in good yields (71-95%) with high l/b ratios (up to 132.4) and excellent TON values (up to 23 760). The ZSM-5 and SO3H group of ligands improved the performances of hydroformylation and reductive amination.

Theoretical study on hydroformylation catalyzed by cationic cobalt(II) complexes

Hydroformylation is one of the most important homogeneous reactions in industrial production. Herein, a density functional theory (DFT) method was employed to investigate two proposed reaction mechanisms of hydroformylation catalyzed by cationic cobalt(II) complexes, the carbonyl dissociative mechanism and the associative mechanism. The calculated results showed that the heterolytic H2 activation is the rate-determining step for both the dissociative mechanism and the associative mechanism, with energy barriers of 26.8 kcal mol-1 and 40.5 kcal mol-1, respectively. Meanwhile, the regioselectivity, the spin multiplicity of the catalyst and the substituent effects on the reaction were also investigated. The most stable cobalt(II) catalyst has a doublet state and the linear aldehyde is the dominant product. In addition, it was found that the energy barrier of the reaction decreased when the electron density of the Co center of the catalyst was increased by changing the ligand. The catalytic activity of the catalyst was proposed to be the best when the PEt2 group of the ligand is replaced by the P(tBu)2 group. This study might not only provide new insights for hydroformylation catalyzed by cobalt but also facilitate theory-guided design of novel transition metal catalysts for hydroformylation.

Differentiating the Yield of Chemical Reactions Using Parameters in First-Order Kinetic Equations to Identify Elementary Steps That Control the Reactivity from Complicated Reaction Path Networks

The yield of a chemical reaction is obtained by solving its rate equation. This study introduces an approach for differentiating yields by utilizing the parameters of the rate equation, which is expressed as a first-order linear differential equation. The yield derivative for a specific pair of reactants and products is derived by mathematically expressing the rate constant matrix contraction method, which is a simple kinetic analysis method. The parameters of the rate equation are the Gibbs energies of the intermediates and transition states in the reaction path network used to formulate the rate equation. Thus, our approach for differentiating the yield allows a numerical evaluation of the contribution of energy variation to the yield for each intermediate and transition state in the reaction path network. In other words, a comparison of these values automatically extracts the factors affecting the yield from a complicated reaction path network consisting of numerous reaction paths and intermediates. This study verifies the behavior of the proposed approach through numerical experiments on the reaction path networks of a model system and the Rh-catalyzed hydroformylation reaction. Moreover, the possibility of using this approach for designing ligands in organometallic catalysts is discussed.

Substrate scope driven optimization of an encapsulated hydroformylation catalyst

Caged complexes can provide impressive selective catalysts. Due to the complex shapes of such caged catalysts, however, the level of selectivity control of a single substrate cannot be extrapolated to other substrates. Herein, the substrate scope using 41 terminal alkene substrates is investigated in the hydroformylation reaction with an encapsulated rhodium catalyst [Rh(H)(CO)3(P(mPy3(ZnTPP)3))] (CAT1). For all substrates, the amount of branched products formed was higher with CAT1 than with the unencapsulated reference catalyst [Rh(H)(CO)2(P(mPy3))2] (CAT2) (linear/branched ratio between 2.14 and 0.12 for CAT1 and linear/branched ratio between 6.22 and 0.59 for CAT2). Interestingly, the level of cage induced selectivity depends strongly on the substrate structure that is converted. Analysis of the substrate scope combined with DFT calculations suggests that noncovalent interactions between the substrate moieties and cage walls play a key role in controlling the regioselectivity. Consequently, these supramolecular interactions were further optimized by replacing the ZnTPP building block with a zinc porphyrin analog that contained OiPr substituents on the meta position of the aryl rings. The resulting caged catalyst, CAT4, converted substrates with even higher branched selectivity.

Continuous-Flow Catalysis Using Phosphine-Metal Complexes on Porous Polymers: Designing Ligands, Pores, and Reactors

Continuous-flow syntheses using immobilized catalysts can offer efficient chemical processes with easy separation and purification. Porous polymers have gained significant interests for their applications to catalytic systems in the field of organic chemistry. The porous polymers are recognized for their large surface area, high chemical stability, facile modulation of surface chemistry, and cost-effectiveness. It is crucial to immobilize transition-metal catalysts due to their difficult separation and high toxicity. Supported phosphine ligands represent a noteworthy system for the effective immobilization of metal catalysts and modulation of catalytic properties. Researchers have been actively pursuing strategies involving phosphine-metal complexes supported on porous polymers, aiming for high activities, durabilities, selectivities, and applicability to continuous-flow systems. This review provides a concise overview of phosphine-metal complexes supported on porous polymers for continuous-flow catalytic reactions. Polymer catalysts are categorized based on pore sizes, including micro-, meso-, and macroporous polymers. The characteristics of these porous polymers are explored concerning their efficiency in immobilized catalysis and continuous-flow systems.

Enantioselective C-H bond functionalization under Co(III)-catalysis

While progress in enantioselective C-H functionalization has been accomplished by employing 4d and 5d transition metal-based catalysts, the rapid depletion of these metals in the earth's crust poses a serious threat to making these protocols sustainable. On the other hand, because of their unique reactivity, low toxicity, and high earth abundance, newer strategies utilizing affordable 3d transition metals have come to the forefront. Among the first-row transition metals, high-valent cobalt has recently attracted a lot of attention for catalytic C-H functionalization with mono and bidentate directing groups. This approach was extended for asymmetric catalysis due to a fairly thorough knowledge of its catalytic cycles. Four major themes have been investigated as a result of this insight: (1) rational design of a chiral Cp#Co(III)-catalyst, (2) chiral carboxylic acid with achiral Cp*Co(III)-catalysts using monodentate directing groups, (3) cobalt/salox-based systems, and (4) cobalt/chiral phosphoric acid-based hybrid systems with bidentate directing groups. Herein, we highlight the recent developments in high-valent cobalt-catalyzed enantioselective C-H functionalization up to October 2023, with the strong belief that the current state-of-the-art can attract considerable interest in the synthetic community, encouraging discoveries in the evolving landscape of asymmetric catalysis.

Cascade Electrocatalytic and Thermocatalytic Reduction of CO2 to Propionaldehyde

Electrochemical CO2 reduction can convert CO2 to value-added chemicals, but its selectivity toward C3+ products are very limited. One possible solution is to run the reactions in hybrid processes by coupling electrocatalysis with other catalytic routes. In this contribution, we report the cascade electrocatalytic and thermocatalytic reduction of CO2 to propionaldehyde. Using Cu(OH)2 nanowires as the precatalyst, CO2 /H2 O is reduced to concentrated C2 H4 , CO, and H2 gases in a zero-gap membrane electrode assembly (MEA) reactor. The thermochemical hydroformylation reaction is separately investigated with a series of rhodium-phosphine complexes. The best candidate is identified to be the one with the 1,4-bis(diphenylphosphino)butane diphosphine ligand, which exhibits a propionaldehyde turnover number of 1148 under a mild temperature and close-to-atmospheric pressure. By coupling and optimizing the upstream CO2 electroreduction and downstream hydroformylation reaction, we achieve a propionaldehyde selectivity of ~38 % and a total C3 oxygenate selectivity of 44 % based on reduced CO2 . These values represent a more than seven times improvement over the best prior electrochemical system alone or over two times improvement over other hybrid systems.

Efficient Alkene Hydroformylation by Co-C Symmetry-Breaking Sites

Alkene hydroformylation is one of the largest industrial reactions on an industrial scale; however, the development of nonnoble heterogeneous catalysts is usually limited by their low activities and stabilities. Herein, we constructed a 1% Co2C/SiO2 catalyst featuring Co-Cvacancy-Co-C symmetry-breaking sites, which generated a polar surface exhibiting a moderate charge density gradient at the localized Co atoms. Comparatively, this catalyst exhibited notable enhancements in the adsorption and activation of the reactants, as well as in the polarity between intermediates. Significantly, the spatial distance between the adsorption sites of intermediates was reduced, thereby effectively decreasing the energy barrier of reaction processes. As the density of the symmetry-breaking sites increased, the turnover number for propene hydroformylation soared to 18 363, exceeding the activity of heterogeneous Co-based catalysts reported thus far by 1 or 2 orders of magnitude, and the catalyst exhibited high stability during the reaction. This study provides a methodology for constructing atomically active sites, which holds great potential for the design and development of highly efficient catalysts.

Cobalt-Catalyzed Asymmetric Hydrogenation: Substrate Specificity and Mechanistic Variability

Asymmetric hydrogenation finds widespread application in academia and industry. And indeed, a number of processes have been implemented for the production of pharma and agro intermediates as well as flavors & fragrances. Although these processes are all based on the use of late transition metals as catalysts, there is an increasing interest in the use of base metal catalysis in view of their lower cost and the expected different substrate scope. Catalysts based on cobalt have already shown their potential in enantioselective hydrogenation chemistry. This review outlines the impressive progress made in recent years on cobalt-catalyzed asymmetric hydrogenation of different unsaturated substrates. We also illustrate the ligand dependent substrate specificity as well as the mechanistic variability in detail. This may well guide further catalyst development in this research area.

Borataalkenes, boraalkenes, and the η2-B,C coordination mode in coordination chemistry and catalysis

Borataalkenes and boraalkenes are the boron-containing isoelectronic analogues of alkenes and vinyl cations respectively. Compared with alkenes, the borataalkene and boraalkene ligand motifs in transition metal coordination chemistry are relatively underexplored. In this review, the synthesis of borataalkene and boraalkene complexes and other transition metal complexes featuring the η2-B,C coordination mode is described. The diversity of coordination modes and geometry in these complexes, and the spectroscopic and structural evidence supporting their assignments is disclosed as well as computational analysis of bonding. The applications of the borataalkene ligand motif in synthetic organic homogeneous catalysis, especially those involving geminal bis(pinacolatoboronates) and 1,4-azaborines, are discussed.

Spectroscopic characterization of carbon monoxide activation by neutral chromium carbides

Spectroscopic characterization of carbon monoxide activation by neutral metal carbides is of essential importance for understanding the structure-reactivity relationships of catalytic sites, but has been proven to be very challenging owing to the difficulty in size selection. Here, we report a size-specific infrared-vacuum ultraviolet spectroscopic study of the reactions between carbon monoxide with neutral chromium carbides. Quantum chemical calculations were carried out to identify the low-lying structures and to interpret the experimental features. The results reveal that the most stable structure of CrC3(CO)2 consists of a CCO ketenylidene unit and that of CrC4(CO)2 has a semi-bridging CO with a very low CO stretching vibrational frequency at 1821 cm-1. The electron structure analyses show that this semi-bridging CO is highly activated through the delocalized Cr-C-C three-center two-electron (3c-2e) interaction between the antibonding orbitals of CO and the metal carbide skeleton. The formation of these metal carbide carbonyls is found to be both thermodynamically exothermic and kinetically facile in the gas phase. The present findings have important implications for the mechanical understanding of the catalytic processes with isolated metal atoms/clusters dispersed on supports.

Ligand Hydrogenation during Hydroformylation Catalysis Detected by In Situ High-Pressure Infra-Red Spectroscopic Analysis of a Rhodium/Phospholene-Phosphite Catalyst

Phospholane-phosphites are known to show highly unusual selectivity towards branched aldehydes in the hydroformylation of terminal alkenes. This paper describes the synthesis of hitherto unknown unsaturated phospholene borane precursors and their conversion to the corresponding phospholene-phosphites. The relative stereochemistry of one of these ligands and its Pd complex was assigned with the aid of X-ray crystal structure determinations. These ligands were able to approach the level of selectivity observed for phospholane-phosphites in the rhodium-catalysed hydroformylation of propene. High-pressure infra-red (HPIR) spectroscopic monitoring of the catalyst formation revealed that whilst the catalysts showed good thermal stability with respect to fragmentation, the C=C bond in the phospholene moiety was slowly hydrogenated in the presence of rhodium and syngas. The ability of this spectroscopic tool to detect even subtle changes in structure, remotely from the carbonyl ligands, underlines the usefulness of HPIR spectroscopy in hydroformylation catalyst development.

Carbon monoxide poisoning: A problem uniquely suited to a medicinal inorganic chemistry solution

Carbon monoxide poisoning is one of the most common forms of poisoning in the world. Although the primary mode of treatment, oxygen therapy, is highly effective in many cases, there are instances in which it is inadequate or inappropriate. Whereas oxygen therapy relies on high levels of a low-affinity ligand (O2) to displace a high-affinity ligand (CO) from metalloproteins, an antidote strategy relies on introducing a molecule with a higher affinity for CO than native proteins (Kantidote,CO > Kprotein,CO). Based on the fundamental chemistry of CO, such an antidote is most likely required to be an inorganic compound featuring an electron-rich transition metal. A review is provided of the protein-, supramolecular complex-, and small molecule-based CO poisoning antidote platforms that are currently under investigation.

Efficient Interfacial Sites between Metallic and Oxidized Cobalt for Propene Hydroformylation

Currently, the hydroformylation of short olefins is operated almost exclusively by using Rh catalysts. Considering the high cost and scarcity of rhodium resources, it is important to develop non-noble metal catalysts toward hydroformylation. Herein, we report an efficient cobalt-based catalyst rich in interfacial sites between metallic and oxidized cobalt species for the hydroformylation of short olefin, propene, under a moderate syngas pressure. The catalyst exhibited a high specific activity of 252 mol molCo-1 h-1 in toluene under 2 bar of propene and 40 bar of CO/H2 mixed gas (CO/H2 = 1:1) at 160 °C. According to mechanistic studies, the interface of metallic and oxidized cobalt species promoted the adsorption of CO and propene. Moreover, the interfacial sites lowered the energy barrier for CO* hydrogenation and C-C coupling compared with metallic cobalt.

Regiodivergent Carbonylation of Alkenes: Selective Palladium-Catalyzed Synthesis of Linear and Branched Selenoesters

An unprecedented regiodivergent palladium-catalyzed carbonylation of aromatic alkenes has been developed. Utilizing commercially available Pd(CH3 CN)2 Cl2 in the presence of 1,1'-ferrocenediyl-bis(tert-butyl(pyridin-2-yl)phosphine) ligand L8 diverse selenoesters are obtained in a straightforward manner. Key to success for the control of the regioselectivity of the carbonylation step is the concentration of the acidic co-catalyst. This general protocol features wide functional group compatibility and good regioselectivity. Mechanistic studies suggest that the presence of stoichiometric amounts of acid changes the properties and coordination mode of the ligand leading to reversed regioselectivity.

Solvent-Controllable C-F Bond Activation for Masked Formylation of α-Trifluoromethyl Alkenes via Organo-Photoredox Catalysis

A solvent-controllable organo-photoredox-catalyzed C-F bond activation for masked formylation of α-trifluoromethyl alkenes with low-priced 1,3-dioxolane as masked formyl radical equivalent has been described. Consequently, a diversity of masked formylated gem-difluoroalkenes and monofluoroalkenes are constructed in moderate to high yields. This approach merits readily available starting materials, mild reaction conditions, and broad substrate scope. The feasibility of this approach has been highlighted by the one-pot masked formylation/hydrolysis sequence to form γ,γ-difluoroallylic aldehydes and late-stage modification of pharmaceutical and natural product derivatives.

Conductive catalysis by subsurface transition metals

The nature of catalysis has been hotly pursued for over a century, and current research is focused on understanding active centers and their electronic structures. Herein, the concept of conductive catalysis is proposed and verified by theoretical simulations and experimental observations. Metallic systems containing buried catalytically active transitional metals and exposed catalytically inert main group metals are constructed, and the electronic interaction between them via metallic bonding is disclosed. Through the electronic interaction, the catalytic properties of subsurface transitional metals (Pd or Rh) can be transferred to outermost main group metals (Al or Mg) for several important transformations like semi-hydrogenation, Suzuki-coupling and hydroformylation. The catalytic force is conductive, in analogy with the magnetic force and electrostatic force. The traditional definition of active centers is challenged by the concept of conductive catalysis and the electronic nature of catalysis is more easily understood. It might provide new opportunities for shielding traditional active centers against poisoning or leaching and allow for precise regulation of their catalytic properties by the conductive layer.

Kinetics of H· Transfer from CpCr(CO)3H to Various Enamides: Application to Construction of Pyrrolidines

The rate constants kH (kD) have been determined at 27 °C for H· (D·) transfer from CpCr(CO)3H(D) to the C=C bonds of various enamides. This process leads to the formation of α-amino radicals. Vinyl enamides with N-alkyl and N-phenyl substituents have proven to be good H· acceptors, with rate constants close to those of styrene and methyl methacrylate. A methyl substituent on the incipient radical site decreases kH by a factor of 4; a methyl substituent on the carbon that will receive the H· decreases kH by a factor of 380. The measured kH values indicate that these α-amino radicals can be used for the cyclization of enamides to pyrrolidines. A vanadium hydride, HV(CO)4(dppe), has proven more effective at the cyclization of enamides than Cr or Co hydrides-presumably because the weakness of the V-H bond leads to faster H· transfer. The use of the vanadium hydride is operationally simple, employs mild reaction conditions, and has a broad substrate scope. Calculations have confirmed that H· transfer is the slowest step in these cyclization reactions.

Carbonylation as a Key Step in New Tandem Reactions - A Route to BODIPYs

Herein, a highly efficient five-step reaction sequence to BODIPYs is presented. The key step is the combination of transition metal-catalyzed in-situ generation of aldehydes and their subsequent organocatalytic activation to yield dipyrromethanes, which are further converted to the corresponding BODIPY. Classic syntheses towards BODIPYs have relied on aldehydes or acid chlorides, which are often not commercially available and rather sensitive to handle. The presented approach starts from readily available and stable alkenes or aryl-bromides, which allows to extend the range of readily available BODIPYs that can be tailored for their specific use. The synthesis of 55 derivatives with overall yields of up to 78 % demonstrates the wide applicability and advantages of the presented method.

Low-temperature hydroformylation of ethylene by phosphorous stabilized Rh sites in a one-pot synthesized Rh-(O)-P-MFI zeolite

Zeolites containing Rh single sites stabilized by phosphorous were prepared through a one-pot synthesis method and are shown to have superior activity and selectivity for ethylene hydroformylation at low temperature (50 °C). Catalytic activity is ascribed to confined Rh2O3 clusters in the zeolite which evolve under reaction conditions into single Rh3+ sites. These Rh3+ sites are effectively stabilized in a Rh-(O)-P structure by using tetraethylphosphonium hydroxide as a template, which generates in situ phosphate species after H2 activation. In contrast to Rh2O3, confined Rh0 clusters appear less active in propanal production and ultimately transform into Rh(I)(CO)2 under similar reaction conditions. As a result, we show that it is possible to reduce the temperature of ethylene hydroformylation with a solid catalyst down to 50 °C, with good activity and high selectivity, by controlling the electronic and morphological properties of Rh species and the reaction conditions.