Rh-catalyzed Hydroformylation Research Articles

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.

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.

Stereodivergent Synthesis of Alkaloid (±)-223A and (±)-6-epi-223A via Rh-Catalyzed Hydroformylation Double Cyclization.

A stereodivergent approach toward total syntheses of Dendrobatid alkaloids 223A and 6-epi-223A is described. The approach features a concise construction of an indolizidine skeleton by Rh-catalyzed domino hydroformylation double cyclization and sequential stereocontrolled transformations such as reductive alkylation or anti-selective α-alkylation of the 5-oxoindolizidine. These stereoselective reactions afford the desired stereochemistry in the targets.

Total Synthesis of (±)-20-epi-Kopsiyunnanine K: A Domino and Stereocontrolled Approach.

A one-pot route to a novel azepane-fused tetrahydro-β-carboline framework from tryptyl-4-pentenamide derivatives has been developed, featuring the Rh-catalyzed hydroformylation double cyclization. Subsequent alkylation in the tetracyclic system proceeded stereoselectively to form a quaternary carbon. The synthesis of (±)-20-epi-kopsiyunnanine K was accomplished through the strategy.

Highly selective and recyclable homogeneous hydroformylation of olefins with [Rh(cod)Cl]2/PPh3 regulated by Et3N as additive

Rh-catalyzed hydroformylation of different olefins toward the corresponding aldehydes were performed under syngas atmosphere in the presence of triethylamine (Et3N) as additive. The influence of various reaction parameters including the phosphine ligands, solvents, additives have been investigated. It was found that, by involving Et3N as additive in the [Rh(cod)Cl]2/PPh3 catalytic system, the conversion of substrates (including cyclic, internal and linear olefins, up to 99%) and chemo/regioselectivity of the products were improved (up to 99%), the applicability for the synthesis of important aldehydes was wider in the absence of solvent. More importantly, the catalytic system could be recycled more than 7 times through vacuum distillation operation and provided a new synthesis method for the pesticide dinotefuran (Tetrahydrofuran-3-formaldehyde) and perfume (Lily aldehyde) intermediates.

Boosting the Hydroformylation Activity of a Rh/CeO2 Single-Atom Catalyst by Tuning Surface Deficiencies

Controlling the interactions between atomically dispersed metal atoms and the support plays significant roles in determining the activity and selectivity of single-atom catalysts. In this report, we tuned the local coordination environment of Rh single atoms on CeO2 via calcination to construct a highly active hydroformylation catalyst. Single-atom Rh/CeO2 calcined at a high temperature exhibits more oxygen vacancies, which lead to the formation of a large amount of low-coordination Rh active species that are more active for hydroformylation. Under the optimum conditions, the best Rh/CeO2 catalyst achieved a TOF at approximately 5000 h–1 with 100% aldehyde selectivity in propylene hydroformylation to butanal. In situ FTIR spectroscopy and in situ XPS characterizations provide strong evidence that Rh on 800 °C-calcined CeO2 is easily activated to form surface HRh(CO)2 active species, favoring propylene adsorption and CO insertion. This work highlights the significance of engineering metal–support interactions in tuning the hydroformylation performance of single-atom catalysts and contributes to mechanistic insights into single-atom Rh-catalyzed hydroformylation reactions.

Rh-catalyzed hydroformylation of allyl acetate toward 4-acetoxybutyraldehyde: The crucial step in production of 1,4-butanediol via hydroformylation/hydrogenation sequence

The synthesis protocol for 1,4-butanediol via two-step hydroformylation-hydrogenation sequence using allyl acetate as the starting material has attracted much attention in industry. In this work, the first-step hydroformylation of allyl acetate determining the overall efficiency of this protocol was studied. Based on the phosphine screening and reaction condition optimization allyl acetate, Xantphos-modified Rh(acac)(CO)2 catalytic system proved highly efficient for hydroformylation of allyl acetate, giving the target product of 4-acetoxybutanal in the yield of 80%. This catalytic system is advantageous with excellent regioselectivity to the linear product of 4-acetoxybutanal as well as the recyclability up to 10 runs without activity loss, demonstrating its remarkable stability required for large-scale application. The control experiments were conducted to shed light on the involved reaction pathways for generation of target 4-acetoxybutanal and the related side-products.

Rhodium-catalyzed hydroformylation of strained dialkenes: Ligand effect on product selectivity and complex coordination mode

We reported the synthesis of new and easily tunable diphosphine ligands L1-L5 based on bis(1H-indol-3-yl)methane. Strained 2,5-norbornadiene and dicyclopentadiene were used as the substrates to elucidate the relationship between ligand structure and product selectivity in Rh-catalyzed hydroformylation. Details in NMR, HRMS and single-crystal X-ray diffraction revealed that the coordination number and oxidation state could change rapidly upon exposure of RhI-L complexes to air. More importantly, the special structure of ligand which led to intramolecular methylene C–H oxidative addition to metal center could facilitate the hydroformylation reaction in an unexpected way.

Iodide-Assisted Pd Catalysis as an Attractive Alternative to Rh Catalysis for the Industrially Relevant Isoselective Hydroformylation of Simple Aliphatic Alkenes

AbstractThe hydroformylation of simple aliphatic alkenes, such as propylene, is one of the largest homogenous catalyzed processes in the chemical industry, producing over 10 million metric tons of different aldehydes each year. Typically, such processes are catalyzed by Co or Rh catalysts, yielding mostly linear aldehydes, such as n-butanal. However, the increasing demand for branched aldehydes, such as isobutanal, triggered further investigation to develop efficient isoselective protocols, which remain scarce. In this Synpacts article, we discuss our recent work on iodide-assisted Pd catalysis as an attractive alternative strategy for the development of isoselective methods. This article is presented considering the state of the art for Rh-catalyzed processes. Additionally, we discuss the limitations and challenges that need to be addressed in order to successfully transfer the technology to industry.1 Introduction2 State of the Art for the Isoselective Rh-Catalyzed Hydroformylation of Unbiased Aliphatic Alkenes2.1 Decomposition-Driven Isoselectivity2.2 Substrate-Dependent Isoselectivity2.3 Equiselective Catalysis2.4 Isoselective Rh Catalysts Bearing Small-Bite-Angle Ligands2.5 Isoselective Rh Catalyst Bearing a Tridentate Ligand2.6 Isoselective Catalysis Driven by Rh Encapsulation2.7 Isoselective Catalysis Driven by Specific Noncovalent Substrate–Ligand Interactions3 Pd-Catalyzed Isoselective Hydroformylation of Unbiased Aliphatic Alkenes3.1 Selectivity Patterns in Pd-Catalyzed Hydroformylation of Alkenes3.2 Unusual Iodide-Assisted Binuclear Pd(I)–Pd(I) Mechanism3.3 Development of Pd-Catalyzed Isoselective Hydroformylation of Unbiased Aliphatic Alkenes4 Conclusions and Outlook

A diphosphoramidite ligand for hydroformylation of various olefins.

A new rotationally hindered diphosphoramidite ligand has been applied to the Rh-catalyzed hydroformylation of various olefins. Good activity as well as excellent regioselectivity toward the formation of linear aldehydes were achieved. Remarkable performances were also observed in the hydroformylation of functionalized olefins, including methyl acrylate, allyl acetate, crotonaldehyde ethylene acetal and styrene.

Solvent effect on mechanistic pathways in Rh-catalyzed hydroformylation of formaldehyde

The homogeneous catalytic hydroformylation of formaldehyde to glycolaldehyde is a key intermediate step for one-step synthesis of ethylene glycol from syngas. The effect of solvent nature on the catalytic response and mechanistic pathway has been rarely studied. A group of parameters (e.g., εr, μ, α, β) describing the solvent electronic features were achieved for a descriptor database and correlated with the hydroformylation activity. The net electron donating ability has been found to govern the selectivity to glycolaldehyde. The DFT calculation demonstrates the stronger electron-donating solvents serve to lower the energy required for the dissociation of Rh-H to form the anionic rhodium species, which induces the anion mechanism that preferentially facilitates the glycolaldehyde generation. The polar aprotic solvents can be protonated in the dissociation of Rh-H to the anionic species and participate in the HCHO activation through the proton transfer from solvent molecules to HCHO, resulting in the formation of hydroxymethyl species.

Selective Rhodium-Catalyzed Hydroformylation of Terminal Arylalkynes and Conjugated Enynes to (Poly)enals Enabled by a π-Acceptor Biphosphoramidite Ligand.

The hydroformylation of terminal arylalkynes and enynes offers a straightforward synthetic route to the valuable (poly)enals. However, the hydroformylation of terminal alkynes has remained a long-standing challenge. Herein, an efficient and selective Rh-catalyzed hydroformylation of terminal arylalkynes and conjugated enynes has been achieved by using a new stable biphosphoramidite ligand with strong π-acceptor capacity, which affords various important E-(poly)enals in good yields with excellent chemo- and regioselectivity at low temperatures and low syngas pressures.

Insight into decomposition of formic acid to syngas required for Rh-catalyzed hydroformylation of olefins

Formic acid (FA) is one kind of important bulk chemicals, which is recognized as a sustainable and eco-friendly energy carrier to transport H2 via dehydrogenation or CO via decarbonylation. Expectantly, FA upon decomposition into H2 and CO could be used as the syngas alternative for hydroformylation. In this paper, the behaviors of FA to release H2 as well as CO following the distinct pathways were carefully investigated for the first time, and then established a new hydroformylation protocol free of syngas. It was found that the atmospheric hydroformylation of olefins with formic acid (FA) as syngas alternative was smoothly fulfilled over Xantphos (L1) modified Rh-catalyst under mild conditions (80 °C, Rh concentration 1 mol %, 14 h), resulting in >90% conversion of the olefins along with the high selectivity to the target aldehydes (>93%). By using FA as syngas source, the side-reaction of olefin-hydrogenation was greatly depressed. The in situ FT-IR and the high-pressure 1H NMR spectroscopic analyses were applied to reveal how FA behaves dually as CO surrogate and hydrogen source over L1-Rh(acac)(CO)2 catalytic system, based on which the deeply insight into the catalytic mechanism of hydroformylation of olefins with FA as syngas alternative was offered.

Computational chemistry considerations in catalysis: Regioselectivity and metal-ligand dissociation

The utility of a range of computational chemistry approaches for the prediction of the regioselectivity for hydroformylation processes and metal-ligand dissociation in a model organometallic system is considered to provide insight about computational strategies for use in catalysis. The hydroformylation reactions investigated are the Rh-catalyzed hydroformylation of terminal alkenes with triarylphosphine and chelating diphosphine ligands. As well, the dissociation of water from a Pt complex is considered to probe method effects on metal-ligand bonding. Several density functional theory (DFT) approaches and ab initio methods are considered. We demonstrate that the quality of the basis set selected for the calculations can play a vital role in the prediction of even the product distribution, and that correcting for basis set superposition error (BSSE) can be very important. As well, the study demonstrates a broad range of predictions achievable using a variety of DFT approaches, which is, as discussed, a manifestation of the challenges that are encountered for calculations involving transition metal molecular species, illustrating the critical need to gauge computational chemistry methods.

One-pot synthesis of aldoximes from alkenes via Rh-catalysed hydroformylation in an aqueous solvent system

Aldoxime synthesis directly starting from alkenes was successfully achieved through the combination of hydroformylation and subsequent condensation of the aldehyde intermediate with aqueous hydroxylamine in a one-pot process.

Rh-catalyzed highly regioselective hydroformylation to linear aldehydes by employing porous organic polymer as a ligand.

In this work, we developed a new structural porous organic polymer containing biphosphoramidite unit, which can be used as a solid bidentate phosphorous ligand for rhodium-catalyzed solvent-free higher olefins hydroformylation. The resultant catalyst demonstrated unprecedently high regioselectivity to linear aldehydes and could be readily recovered for successive reuses with good stability in both catalytic activity and regioselectivity.

Butadiene hydroformylation to adipaldehyde with Rh-based catalysts: Insights into ligand effects

Rh-catalyzed hydroformylation of butadiene to adipaldehyde is a promising alternative route for producing valuable C6 compounds such as adipic acid and hexamethylenediamine. Fundamental insights into reaction pathways, aimed at enhancing adipaldehyde yield, were obtained from temporal concentration profiles and in situ ReactIR studies of butadiene hydroformylation on Rh complexes at 80 °C and 14 bar syngas (molar CO/H2 = 1) pressure in a batch reactor. Specifically, the effects of operating conditions and eight commercially available ligands on activity and selectivity were systematically investigated. It was found that the adipaldehyde selectivity is independent of the ligand/Rh ratio, rhodium concentration, butadiene concentration and syngas pressure, but significantly dependent on the type of ligand used. For example, while the DIOP ligand provided an adipaldehyde yield of ∼40% with butadiene as a substrate, the 6-DPPon ligand gave a maximum adipaldehyde yield of ∼93% with 4-pentenal as substrate. Furthermore, the adipaldehyde selectivity correlates well with the natural bite angle of the various ligands. ReactIR studies suggest that the preferential formation of the stable rhodium η3-crotyl complex with the various Rh complexes may be the main reason for the low adipaldehyde selectivity.

A novel homogeneous catalysis–liquid/solid separation system for highly effective recycling of homogeneous catalyst based on a phosphine-functionalized polyether guanidinium ionic liquid

Herein we report a novel homogeneous catalysis–liquid/solid separation catalytic system for highly effective recycling of homogeneous catalyst based on a phosphine-functionalized polyether guanidinium ionic liquid (P-PolyGIL) with a room temperature liquid/solid phase transition characteristic. This novel catalytic system has perfectly integrated the advantages of both the homogeneous and biphasic catalysis to realize the combination of the high activity, easy catalyst recycling and long service-life of the catalyst without a significant loss of the activity, selectivity and Rh for more than 30 cycles in the Rh-catalysed hydroformylation of higher olefins. The long service-life of the catalyst could be attributed to the efficient and practical strategy of the catalyst separation.

XL-Xantphos: Design and Synthesis of a Mechanistic Probe of Xantphos O-Coordination in Catalytic Reactions

The synthesis and characterization of an analog of the Xantphos ligand that is geometrically incapable of coordination of the xanthene bridging oxygen atom is reported. This new ligand, XL-Xantphos, ((9,9-dimethyl-9H-xanthene-4,5-diyl)bis(4,1-phenylene))bis(diphenylphosphane), was studied in homogeneous, catalytic reactions for comparison with Xantphos. The XL-Xantphos ligand performed essentially identically to Xantphos in Rh-catalyzed hydroformylation of 1-octene, which suggests that the high regioselectivity for linear aldehyde is due to the large bite angle of these ligands and is not influenced by oxygen coordination to the metal. The Pd-catalyzed amidocarbonylation of 4-bromoanisole with dimethylhydroxylamine hydrochloride similarly showed no difference between Xantphos and XL-Xantphos. Computations on Pd(II) phosphine complexes at the DLPNO–CCSD(T) level of theory indicated that these ligands have different preferences for cis and trans coordination modes. The XL-Xantphos ligand has a thermodynamic...

Preparation and Characterization of Rh/MgSNTs Catalyst for Hydroformylation of Vinyl Acetate: The Rh0 was Obtained by Calcination

A simple and practical Rh-catalyzed hydroformylation of vinyl acetate has been synthesized via impregnation-calcination method using silicate nanotubes (MgSNTs) as the supporter. The Rh0 (zero valent state of rhodium) was obtained by calcination. The influence of calcination temperature on catalytic performance of the catalysts was investigated in detail. The catalysts were characterized in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectrometer (XPS), atomic emission spectrometer (ICP), and Brunauer–Emmett–Teller (BET) surface-area analyzers. The Rh/MgSNTs(a2) catalyst shows excellent catalytic activity, selectivity and superior cyclicity. The catalyst could be easily recovered by phase separation and was used up to four times.