Hydroformylation Reaction Research Articles

Sidearm modified phosphine ligands for Rh complex-catalyzed hydroformylation: Mechanistic pathway and structure-activity relationship

Development of high-performance phosphine ligands is an effectual strategy to improve the homogeneous hydroformylation reaction. This study designed a series of amide/ester sidearms-modified phosphine ligands with different characteristics (e.g., proton affinity, steric hindrance) for homogeneous Rh-complex in hydroformylation of formaldehyde. The sidearms-modified ligands with the stronger proton affinity serve to transfer proton from the hydrido rhodium species to the activated formaldehyde via the sidearms to generate the critical hydroxymethyl rhodium species that favours the hydroformylation to glycolaldehyde, yielding significantly improved reaction rates (twice as much as PPh3). The bulky sidearm with larger steric hindrance can stretch the hydrogen bond between the product and the sidearm, suppressing the by-product production and improving the target selectivity. A potential reaction mechanism involving sidearm-induced deprotonation and inner-molecule proton transfer was proposed for the sidearm-modified phosphine ligands coordinated Rh complex based on the DFT calculation and experimental study. This study can trigger the innovative phosphine ligand design with special functional sidearms for hydroformylation.

Diverse Catalytic Applications of Phosphine Oxide‐Based Metal Complexes

AbstractPhosphine oxides are an interesting class of compounds possessing tetracoordinate and pentavalent phosphorus atoms and have been employed in a wide range of applications including reagents in organic synthesis, metal extractants, flame retardants, pharmaceuticals, and bioactivity studies. Among all, the degree of basicity of phosphoryl oxygen driven by the nature of substituents influences the electronic properties of the central metal in a complex toward the diversified catalytic processes. Further, the presence of heteroatoms adjacent to the central phosphorus atom enhances the nucleophilicity of the phosphoryl oxygen atom. In view of this, the present review covers the past two decades of remarkable catalytic versatility of P=O‐based metal complexes and describes the governing factors influencing the structural properties and the resultant coordination behavior. Interestingly, some of the P=O bond distances of metal complexes are either longer or shorter compared to their free ligands, indicating the catalytic activity. These complexes can effectively catalyze a wide range of chemical reactions including polymerizations, C−C and Si−C bond activations, oxidation, reduction, hydroformylation, hydrophosphination, hydrogenation and cyclization reactions. Furthermore, this review emphasizes the impact of substituents, solvents, additives, light, and temperature on the catalytic efficiency.

Influence of support on Rh-Co bimetallic catalysts for ethylene hydroformylation

Bimetallic Rh- and Co-based catalysts are promising materials for the heterogenous ethylene hydroformylation reaction. Here, the influence of a mesoporous silica (SBA-15) support on Rh and Co bimetallic interactions was investigated through a comparison with silica gel and gamma-alumina supports. The bimetallic catalyst supported on mesoporous silica (RhCo3/SBA-15) showed the best C3 oxygenate yield among the three bimetallic catalysts. In-situ vibrational studies suggested moderate binding of the gem-dicarbonyl and Rh(CO)(C2H4) intermediates due to this bimetallic interaction that led to improved hydroformylation performance. Kinetic studies revealed a lower hydroformylation barrier for the bimetallic compared to a Rh monometallic catalyst, and in-situ X-ray absorption spectroscopy investigations showed clear Rh-Co alloy formation on RhCo3/SBA-15. The bimetallic enhancement effect from the interaction with the mesoporous silica support shown here can be further optimized to design olefin hydroformylation catalysts.

Novel fragrant aldehydes from (1R,5R)-sabinene: An experimental study supported by DFT calculations revealing an unusual hydroformylation mechanism

The fragrance industry continually searches for compounds that introduce new scent notes or improve existing ones. Herein, we report a methodology for obtaining two novel aldehydes, potentially interesting for application in fragrance formulations, via rhodium-catalyzed hydroformylation of (1R,5R)-sabinene, a biorenewable monoterpene available in many essential oils. One of the aldehydes, which retained the original sabinene skeleton, was derived from the hydroformylation of the exocyclic C-C double bond through the accepted hydroformylation mechanism. The other aldehyde arose from the interaction of rhodium with the cyclopropane ring through an unusual mechanism, which resulted in the cyclopropane ring cleavage, forming a product that shares structural similarities with established fragrant molecules. The selectivity was controlled by adjusting the reaction conditions (temperature, pressure, P-ligand, and P/Rh ratio). Each aldehyde was obtained in a 70–80 % yield, depending on the reaction conditions. Combining our experimental findings with DFT calculations allowed us to propose an unusual hydroformylation reaction mechanism involving cyclopropane moiety in vinylcyclopropanes.

Stereoselective Synthesis of anti-2,4-Disubstituted Tetrahydrofurans via a Pd-Catalyzed Hayashi-Heck Arylation and Rh-Catalyzed Hydroformylation Sequence.

A catalytic, two-step protocol for the expedient synthesis of anti-2,4-disubstituted tetrahydrofurans is described. In the first step, an enantioselective and regioselective Pd-catalyzed Hayashi-Heck arylation was developed using (R)-hexaMeOBiphep to generate 5-aryl-2,3-dihydrofurans. A subsequent Rh-catalyzed hydroformylation step proceeds at low Rh loading with high regio- and diastereoselectivity for the anti-2,4-disubstituted tetrahydrofuran isomer. Key to the development of the hydroformylation reaction was the utilization of either (R)-Me-i-Pr-INDOLphos or (R,R)-Ph-BPE to control the regioselectivity and provide the kinetic product isomer.

Porous Organic Polymers Supported Heterogeneous Catalysts for Hydroformylation Reactions

AbstractSince Otto Roelen revealed the accidental discovery of the hydroformylation process while exploring Fischer‐Tropsch synthesis, this chemical process of olefins with syngas has subsequently become the main source of aldehyde products. Compared to homogeneous systems, heterogeneous hydroformylation systems can avoid homogenous separation and lower the loss of valuable metals. Porous organic polymers (POPs) are one of porous materials that are interconnected by strong covalent bonds. By modifying the substrate structures, they may encapsulate various metal atoms and show remarkably high selectivity and activity for hydroformylation processes. In this review, we mainly focus on systematically summarizing recent developments, synthesis, and catalytic research on POPs supported catalysts in hydroformylation reactions. Lastly, we also discuss the prospects and challenges for future studies for the POPs supported metal catalysts.

In Situ XAS Diagnostics of Reductive Hydroformylation Reaction in Segmented Flow Under Elevated Pressure and Temperature

In Situ XAS Diagnostics of Reductive Hydroformylation Reaction in Segmented Flow Under Elevated Pressure and Temperature

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.

Constructing Co@C nanoparticles with chainmail-structure for highly efficient hydroformylation of 1-hexene

Constructing highly active noble-metal-free heterogeneous catalysts is the crux for the hydroformylation of long-chain α-olefins. Herein, novel chainmail-structured cobalt oxide nanoparticles (CoO@C|SBA-15) are fabricated by the channel confinement strategy, which display excellent activity for the 1-hexene hydroformylation. Specifically, the obtained catalyst shows 100% 1-hexene conversion and 94% heptanal selectivity, as well as up to 2.0 linear to branch (l/b) ratio, outperforming most of heterogeneous noble metal catalysts. Remarkably, in-situ DRIFT spectra combined with density functional theory calculations disclosed the metallic Co derived from in-situ reconstruction of CoO is the key active site for 1-hexene hydroformylation. Specifically, the reconstructed Co site is responsible for the adsorption of 1-hexene, and the graphite carbon layer promotes the adsorption of H2 and CO by interacting with the reconstructed Co. Moreover, the graphite carbon layer provides a strong protective effect on the internal cobalt active sites and thus enhances the catalytic stability during the harsh condition. This work provides a new method for designing the low-cost heterogeneous catalyst and emphasizes the intrinsic active sites for 1-hexene hydroformylation reaction.

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.

Synthesis and Characterization of Co(II) Substituted Keggin‐Type Polyoxometalates as Novel Catalysts for the Hydroformylation of 1‐Hexene in a Thermomorphic Solvent System

AbstractPolyoxometalates (POMs) are a unique class of metal oxides, being of huge interest for the catalysis society. CoII‐substituted phosphomolybdate POMs (namely H7[PCoMo11O40], H11[PCo2Mo10O40] and H15[PCo3Mo9O40]) have been successfully synthesized for the first time. The structure of the new CoII substituted POMs was solved by single‐crystal X‐ray diffraction as well as vibrational (FT‐IR and Raman) and nuclear magnetic/electron paramagnetic resonance (NMR and EPR) spectroscopy and found to be of the Keggin‐type. The Co‐POMs were then applied as molecular catalysts for the hydroformylation of 1‐hexene in a thermomorphic solvent mixture of water and 1‐butanol. This is the very first example of a 1st row transition metal POM acting as a hydroformylation catalyst achieving 46 % heptanal yield. The best results were obtained using H11[PCo2Mo10O40] as a catalyst at 140 °C, 150 bar CO/H2 1 : 2, and a reaction time of 4 h, paving the way for new POM‐based catalysts in hydroformylation reactions.

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.

Grafting EDTA in UiO-66 to modulate the microenvironment of Rh for 1-hexene Hydroformylation

Oriented designing the microenvironment of catalytic sites is essential for understanding catalytic processes. In this work, EDTA was first grafted in UiO-66 and then chelated Rh to obtain an efficient catalyst for 1-hexene hydroformylation reaction. EDTA not only served as a chelation site for Rh immobilization in UiO-66, but also markedly influenced the structure and properties of Rh/UiO-66. The incorporation of EDTA reduced the micropore content and suppressed the formation of heavy products. Moreover, the grafted EDTA regulated the electronic state of Rh effectively to improve the CO and propene adsorption, thus constructing an appropriate microenvironment for hydroformylation. Therefore, EDTA-modified Rh/U-E catalyst exhibited higher aldehydes yield, TOF and stability than Rh/U without EDTA. The dual role of EDTA in anchoring Rh sites and modulating the microenvironment for hydroformylation provides more prospects for designing customized MOFs-based catalysts.

Adjacent MnOx clusters enhance the hydroformylation activity of rhodium single-atom catalysts

Hydroformylation reactions promoted by Rh single-atom catalysts typically exhibit a negative reaction order for CO and a positive reaction order for H2 and alkenes. To enhance the catalytic activity, efforts have been concentrated on reducing the CO adsorption strength and/or enhancing the hydrogenation capacity at Rh sites. This report introduces an optimized Rh single-atom catalyst, utilizing positively charged Mn species to weaken the CO adsorption strength. Our strategy involves placing MnOx clusters in the proximity to the Rh single atom. This arrangement allows the reduction of Rh3+ to produce electronically deficient Rhδ+ species (1 < δ < 2), rather than the usual formation of the lower valence state Rh+ species. The weakened CO adsorption strength on the more positively charged Rhδ+ results in reduced CO coverage on the Rh active site, and enhanced adsorption of propylene. Our mechanistic study reveals that H2 and CO adsorption on Rh catalyzes the reduction of adjacent Mn(IV) species, inducing the formation of a Rh-MnOx paired active site. The neighboring MnOx clusters hinder the extensive reduction of Rh3+ to Rh+. This study presents MnOx as an inorganic ligand in Rh-MnOx pair site modifies the electronic properties of Rh sites to modulate the hydroformylation activity of Rh single-atom catalysts.

Cascade Electrocatalytic and Thermocatalytic Reduction of CO2 to Propionaldehyde

AbstractElectrochemical 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/H2O is reduced to concentrated C2H4, 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.

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.

Bifunctional heterogeneous catalyst: A sustainable route for cyclic acetals synthesis through tandem hydroformylation-acetalization reaction

A novel sustainable approach for the synthesis of 2-ethyl 1,3 dioxolane and various short to long-chain or aromatic cyclic acetals through a tandem hydroformylation-acetalization reaction using Rh oxide nanoparticle supported on zirconium phosphate has been established. The Rh oxide nanoparticle supported on zirconium phosphate was synthesized and characterized by various physicochemical methods. The SEM and TEM analysis revealed the average particle size of rhodium oxide was found to be ∼7.56 nm in 2%Rh@ZrP catalyst. Furthermore, the synthesized catalyst was employed to carry out a tandem hydroformylation reaction in a green solvent (ethylene glycol). Experimental results demonstrated that 2 wt.% of Rhodium on zirconium phosphate efficiently activated olefins, leading to the selective formation of cyclic acetals (60–99%) at 80°C for 6 h. In this cascade reaction, significant selectivity towards the desired product, linear cyclic acetals was observed for styrenes. This can be attributed to highly dispersed Rh oxide nanoparticles and plentiful acidic sites on the zirconium phosphate supports, which played a crucial role in tandem hydroformylation and acetalization reactions. The catalyst exhibited the ability to be reused three times without losing significant catalytic activity or selectivity. This is the first report on the synthesis of a fuel additive and other cyclic acetals via a tandem hydroformylation-acetalization reaction using heterogeneous catalysts.

MOF‐Supported Heterogeneous Catalysts for Hydroformylation Reactions: A Minireview

AbstractTransition metal‐catalyzed hydroformylation reaction of olefins is one of the most important transformations in the perspective of both industrial applications and academic research. This synthetic process provides a straightforward and easy way for the transformations of inexpensive feedstock (mostly different alkene molecules) to valuable aldehyde compounds, which are considered as major building blocks for several essential chemical products. Inspired and motivated by the tremendous success of homogeneous catalysis for hydroformylation reactions, paramount interests have been raised for the design and development of active heterogeneous catalysts owning advantages from both molecular and material sciences. Crystalline metal‐organic frameworks (MOFs) as solid support to immobilize active catalysts for the hydroformylation reaction have shown appealing promises as heterogeneous catalysts. This review sketches out a decade of developments of MOF‐based heterogeneous catalysts for the hydroformylation of olefins while discussing both advantages and limitations for their implementation beyond the lab scale.

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.

Modular synthesis of triphenylphosphine-derived cage ligands for rhodium-catalyzed hydroformylation applications.

Four new triphenylphosphine-derived cage ligands were modularly synthesized via dynamic imine chemistry (DIC), and their absolute structures were characterized by single crystal X-ray diffraction (SXRD), nuclear magnetic resonance (NMR) and high resolution mass spectroscopy (HRMS). In contrast to small-molecule analogues, cage ligands demonstrate superior activity and selectivity. The Rh/Cage-L2 catalyst exhibits remarkable performance with an aldehyde selectivity of 89%, accompanied by a TOF value of 2665 h-1 and an l/b ratio of 2.60, thereby showcasing leading activity, chemical selectivity, and regioselectivity in the realm of homogeneous catalysts that rely on triphenylphosphine ligands. The reason for the formation of a higher l/b ratio, with a 3.84 kJ mol-1 difference in the energy of the rate-determining step, has been explained through density functional theory (DFT) calculations. In addition, a Janus-type PPh3-Au complex has been discovered during the study of the coordination of cage ligands, offering partial corroboration for the single coordination mechanism of these cage ligands. The large steric hindrance effect of cage ligands is believed to play a pivotal role in the hydroformylation reaction. This work highlights the potential application of cage ligands and inspires future efforts in the search of highly selective and efficient organometallic catalysts.