Supported Ionic Liquid Phase Research Articles

A Surface-Active Pt(II) bis-N-Heterocyclic Carbene (NHC) Complex for Interface-Enhanced Supported Ionic Liquid Phase (SILP) Catalysis.

We present the preparation and investigation of a fluorine-free surface-active bis-N-heterocyclic carbene (NHC) platinum(II) complex - trans-[Pt(mPEG3C8Im)2Cl2] - for interface-enhanced supported ionic liquid phase (SILP) catalysis within a group of (mPEGn)-substituted ionic liquids (ILs) ([(mPEGn)2Im][A] ILs). The complex was characterized by means of single-crystal X-ray diffraction (scXRD) analysis and multinuclear (1H, 13C, 195Pt) NMR spectroscopy, indicating the presence of two almost equimolar syn-anti rotamers of the square-planar complex in solution. Angle-resolved X-ray photoelectron spectroscopy (ARXPS) revealed pronounced interface-accumulation of trans-[Pt(mPEG3C8Im)2Cl2] in IL solutions of [(mPEG2)2Im][A] (A- = I- and PF6-).

Influence of Ionic Liquid Film Thickness and Flow Rate on Macrocyclization Efficiency and Selectivity in Supported Ionic Liquid-Liquid Phase Catalysis.

Supported ionic-liquid phase (SILP) technology in a biphasic setting with n-heptane as the transport phase was applied to the Ru-alkylidene-N-heterocyclic carbene (NHC) catalyzed macrocyclization of α,ω-dienes to elucidate the effect of ionic liquid (IL)-film thickness, flow rate as well as substrate and product concentration on macrocyclization efficiency, and Z-selectivity. To understand the molecular-level behavior of the substrates and products at the n-heptane/IL interphase, atomistic molecular dynamics simulations were conducted and correlated with experimental observations. The thickness of the IL layer strongly influences the Z/E ratio of the products in that a thin IL layer favors higher Z/E ratios by confining the catalyst between the pore wall and the liquid-liquid interphase whereas a thick IL layer favors formation of the E-product and Ru-hydride catalyzed isomerization reactions. Also, macrocyclization efficiency, expressed by the ratio of oligomers/macromonocycle (O/MMC), is influenced both by the flow rate and the thickness of the IL layer.

Hydroformylation of Alkenes by Supported Ionic Liquid Phase (SILP) Catalysis

Hydroformylation of olefins forms aldehydes which are valuable final products as well as intermediates in synthesizing bulk chemicals like alcohols, amines, and esters with a yearly world production of about 12 Mt. Industrial hydroformylation processes are essentially homogeneously catalyzed systems with an economic incitement for improvement by easy separation of products and reuse of catalysts, high reactivity and selectivity by using new catalysts, novel processes and alternative methodologies.One such potential candidate for an alternative catalyst is a Supported Ionic Liquid- Phase (SILP) catalyst comprising “heterogenized” homogeneous ionic liquid (IL) catalyst systems on a porous support. Such catalysts make it possible to apply the much preferred fixed bed continuous flow process design which overcomes the troublesome and energy demanding separation of the products from the reaction mixture obtained in the traditional homogenous batch process.In our previous and very recent studies [1-2], we have prepared SILP catalysts containing immobilized Rh-complexes of TPPTS-Cs3 in 1-butyl-3-methylimidazolium octylsulfate ([BMIM][n-C8H17OSO3]) on SiO2 support and investigated the influence of IL loading on the catalytic activity. The influence of other supports : SBA-15, MCM-41, Al2O3, ZrO2 and TiO2 has also been studied and the catalytic activity compared to the SiO2 SILP catalyst. Finaly we will report on a comparison on the catalytic activity of the SiO2 SILP catalyst by use of the ligand precurser TPPTS-Cs3 and the much cheaper TPPTS-Na3 salt. References. H. N. T. Ha, D. T. Duc, T. V. Dao, M. T. Le, A. Riisager, R. Fehrmann. Catal. Commun. 25, 136-141 (2012)Nguyen, V. C., Do, V. H., Truong, D. D., Pham, T. T., Dinh, P. K., Vu, T. L., Garcia-Suarez, E. J., Riisager, A., Fehrmann, R., Le, M. T. Res. Chem. Int..49, 6, 2383-2398 (2023).

Unlocking the Fluorine-Free Buoy Effect: Surface-Enriched Ruthenium Polypyridine Complexes in Ionic Liquids.

Controlling the local concentration of metal complexes at the surface of ionic liquids (ILs) is a highly sought-after objective due to its pivotal implications in supported ionic liquid phase (SILP) catalysis. Equally important is to avoid per- and polyfluorinated substances due to environmental concerns. Herein, we investigate the surface enrichment of Ru polypyridyl complexes with fluorine-free alkylic side groups of varying lengths and shapes, using the hydrophilic IL [C2C1Im][OAc] as solvent. Additional charged carboxylate groups are included into the polypyridyl ligands to increase the solubility of the complex in the IL. When the ligand system is functionalized with long and hydrophobic alkyl side chains, the complex predominantly localizes at the IL/vacuum interface, as deduced from angle-resolved X-ray photoelectron spectroscopy. Conversely, in the presence of short or more bulky substituents, no surface enrichment is observed. This buoy-like behaviour with fluorine-free side groups is explored for 0.05 %mol to 1 %mol solutions. Intriguingly, surface saturation occurs at approximately 0.5 %mol, which is beneficial to the efficient operation of catalytic systems featuring high surface areas, such as SILP catalysts.

Tailoring the Surface Enrichment of a Pt Catalyst in Ionic Liquid Solutions by Choice of the Solvent

AbstractThe so‐called buoy‐effect, that is, the targeted surface enrichment of a Pt catalyst dissolved in ionic liquids (ILs), is achieved by attaching perfluorinated alkyl chains to the ligand system, which drags the metal complex toward the interface. Using angle‐resolved X‐ray photoelectron spectroscopy, it is demonstrated how this surface enrichment can be tailored by variation of the solvent IL. In [CnC1Im][PF6] ILs (n = 2, 4, 8), the surface is fully saturated with the complex at 10%mol bulk content, while in [C4C1Im][Tf2N] only at 20%mol saturation is observed. At low catalyst concentrations of 1%mol, where saturation is not yet reached, the enrichment increases with decreasing length of the IL alkyl chain. As a general rule, the degree of surface enrichment decreases with the decrease in surface tension of the solvent IL, that is, in the order [C2C1Im][PF6] > [C4C1Im][PF6] > [C8C1Im][PF6] > [C4C1Im][Tf2N]. In ILs with very low surface tension, enrichment is even suppressed. These results reveal the surface tension of the solvent IL as rational parameter for tailoring the interfacial structure of IL‐based catalyst systems, such as supported ionic liquid phase (SILP) catalysis, where the nature of the IL/gas interface is expected to strongly influence the performance of the process.

Construction of trifloaluminate ionic liquid catalyst on the silica surface dedicated for continuous flow Diels-Alder synthesis

Supported ionic liquid phases (SILP) are efficiently use for the construction of highly active, heterogeneous and recyclable catalysts. In this study, three strategies towards chemical immobilization of trifloaluminate ionic liquid catalyst into microporous/mesoporous silica support were investigated. The order of silica surface modification with trifloaluminate ILs components had crucial influence on the catalytic activity and stability which was tested in the model Diels-Alder reaction between isoprene and maleic anhydride in acetonitrile at room temperature. The best catalytic performance (maleic anhydride conversion > 97% in ten reaction cycles) was achieved for catalyst created through the synthesis of trifloaluminate ionic liquid in the first step with further bounding to the silica surface using 25 wt% of ionic liquid loading. The effective transformation of the Diels-Alder reaction to continuous flow synthesis led to 97% maleic anhydride conversion over 432 h with a TOF of 104.3 h−1 and significantly improved process sustainability.

Self-Assembled Supported Ionic Liquids.

Separation and reuse of the catalytically active metal complexes are persistent issues in homogeneous catalysis. Supported Ionic Liquid Phase (SILP) catalysts, where the catalytic center is dissolved in a thin film of a stable ionic liquid, deposited on a solid support, present a promising alternative. However, the dissolution of the metal center in the film leaves little control over its position and its activity. We present here four novel, task-specific ionic liquids [FPhn ImH R]I (n=1, 2; R=PEG2 , C12 H25 ), designed to self-assemble on a silica surface without any covalent bonding and offering a metal binding site in a controlled distance to the support. Advanced multinuclear solid-state NMR spectroscopic techniques under Magic Angle Spinning, complemented by molecular dynamics (MD) simulations, allow us to determine their molecular conformation when deposited inside SBA-15 as a model silica support. We provide here conceptual proof for a rational design of ionic liquids self-assembling into thin films, opening an avenue for a second, improved generation of SILP catalysts.

From a Batch to a Continuous Supported Ionic Liquid Phase (SILP) Process: Anhydrous Synthesis of Oxymethylene Dimethyl Ethers

AbstractOxymethylene dimethyl ethers (OMEn; CH3(−OCH2)n−OCH3) are promising sustainable synthetic fuels when produced from CO2 and green H2. The synthesis pathway presented here overcomes synthetic problems and includes the reaction of dimethoxymethane (OME1) with molecular gaseous formaldehyde in a novel continuous, anhydrous reaction setup. An initially performed wide batch‐catalyst screening highlighted the salts M[NTf2]x with M=Cu+, Co2+ and Mg2+ as especially interesting catalysts (NTf2=N(SO2CF3)2). Supported ionic liquid phase (SILP)‐catalysts were prepared on this basis and demonstrated the successful synthesis of OMEn in a continuous process. The SILP‐catalysts immobilized in the IL EMIM[BF4] showed a fast and strong deactivation, but those with the IL EMIM[NTf2] showed excellent catalytic performance and stable results in continuous operations exceeding 19 h. The influence of the weight hourly space velocity (WHSV), the reaction temperature as well as the storage conditions of the catalysts (inert vs non‐inert) were investigated. 90 °C was identified as ideal reaction temperature. High feed‐gas flows (WHSV=15.8 h−1) are preferable in terms of product selectivity SOME2‐5>90 mol‐ % with an OME1 conversion XOME1=5.10 mol‐ % at the same time. We also demonstrated that the catalysts can be stored in air for 50 days without loss of activity. The SILP‐catalysts were analyzed by NMR and IR spectroscopy. Furthermore, the thermodynamics of the reaction mechanism of some selected catalysts was calculated by DFT theory to this reaction.

Dynamic tuning of naked ruthenium clusters/nanoparticles in ionic liquids cages to boost CO2 hydrogenation to formic acid

The reduction of atmospheric CO2 is indeed a major challenge for modern life due to its increase as a result of the intensified contemporary industrial activities and its contribution to global warming. One of the most desirable approaches to accomplish this goal is to convert CO2 into C1 feedstocks, such as formic acid (FA). In this regard, naked ruthenium clusters and nanoparticles (1.8 ± 0.3 nm) are prepared by magnetron sputtering into different supported ionic liquid phases (SILPs) that demonstrated remarkable efficiency in producing a total of 2.2 M of free FA with a TONs of 7305 in 1-Butyl-3-methylimidazolium acetate ionic liquid media at 87 °C. The higher efficiently is related to the hydrophobic/hydrophilic effect presents in the ionic liquid-cages of the SILPs akin to the micelle nano (micro)reactors, which act as catalytic membranes enabling the tuning of FA production. DFT calculations support the mechanistic approach followed the hydrogenation of HCO3* to FA.

Tuning catalyst performance in the SILP-catalyzed gas-phase hydroformylation of but-1-ene by choice of the ionic liquid

For the industrially relevant hydroformylation of but‑1-ene the concept of supported ionic liquid phase (SILP) has been applied previously. In this work, we have studied the influence of the type of ionic liquid (imidazolium and phosphonium based cations, various anions) on the solubility of the three reagents but‑1-ene, carbon monoxide and hydrogen. For the olefin, the predicted solubility values were determined using the COSMO-RS software tool. These data were compared to the experimentally determined values. A correlation between the predicted solubility and the observed activity within similar ILs could be observed. The highest activity could be obtained with the IL [N1888][NTf2]. A variation of the olefin chain length supported the observed correlation between solubility and activity. With increasing chain length, the activity of the SILP catalyst also increased. For the undesired consecutive reaction leading to aldols it was found that the substrate solubility does not significantly influence the activity or hydrocarbon accumulation under the used reaction conditions. The anion had a more pronounced effect on the accumulation of aldols, with hydrophilic Cl− and [EtOSO3]− showing lowest accumulation as well as aldol formation activity, while [NTf2]− showed highest values for both accumulation and formation activity. It was shown that the Kamlet-Taft-parameter β is a suitable value to be correlated with activity and accumulation for different ILs.

Supported Ionic Liquid Phase (SILP) Allylic Alkylation of Amines in Continuous Flow.

We present the use of Pd-complex-containing supported ionic liquid phases (SILPs) as a novel approach for continuous-flow allylic alkylation of N-nucleophiles. This immobilization strategy gave simple access to air-tolerating catalyst frameworks, providing rapid and convenient access to various achiral and chiral N-allylation products. Under optimized conditions, the flow-reaction could be maintained for 3.5 hours with constant product output; meanwhile, only a marginal 0.7 wt % of ionic liquid leaching and no detectable palladium-complex leaching could be observed.

Structure and Surface Behavior of Rh Complexes in Ionic Liquids Studied Using Angle-Resolved X-ray Photoelectron Spectroscopy

We present an ARXPS study on the surface composition and interfacial behavior of commercial [Rh(COD)2][TfO] in [C2C1Im][TfO], [C4C1Im][TfO], [C8C1Im][TfO], and [C2C1Im][EtOSO3]. The complex was found to be non-intact in a solution of these ILs through the loss of COD ligands, accompanied by the depletion of the metal center from the IL/vacuum interface. Increasing the chain length of the aliphatic substituent on the imidazolium cation of the [TfO]−-based ILs led to a more pronounced depletion from the interface, due to the higher surface affinity of the solvent cations with the longer alkyl chains. The loss of COD ligands offered facile in situ ligand substitution with surface-active TPPTS to afford a moderate increase in the surface concentration of Rh. We propose the formation of a Schrock−Osborn-type catalyst [Rh(COD)(TPPTS)2][TfO]. Information on the surface composition and targeted design of the gas/IL interface is highly relevant for applications in IL-based catalytic systems, such as in supported ionic liquid phase (SILP) catalysis.

Wetting Behavior and Support Interactions in Imidazolium-Based Supported Ionic Liquid Phase Materials─A Systematic Study by Solid-State Nuclear Magnetic Resonance Spectroscopy

Supported ionic liquid phase (SILP) catalysts are an extremely promising class of materials that combine advantageous concepts from both homogeneous and heterogeneous catalysis. Optimized SILP catalysts should exhibit a thin, homogeneous, and continuous film of the ionic liquid (IL) to avoid pore blocking and to ensure a good accessibility of the catalyst. Yet, the interactions between the IL and the support, which determine the formation of such a film, are still poorly understood. We investigate here in a systematic way the deposition of three imidazolium-based ILs on silica supports with different surface areas and morphologies using 1H magic angle spinning solid-state nuclear magnetic resonance spectroscopy. We demonstrate that the point of complete surface wetting can be determined by the disappearance of the 1H resonance of isolated silanol groups and that this point depends both on the textural properties of the support material and the chemical properties of the IL. 1H chemical shifts also provide valuable insight into hydrogen bonding interactions within the IL and between the IL and the support. They indicate cleavage of the anion–cation hydrogen bonds upon IL deposition and the formation of new hydrogen bonds with the silica surface.

Supported ionic liquids for effective ruthenium olefin metathesis

Supported olefin metathesis catalysts have attracted considerable interest for over two decades, regarding their facile separation, reusability and decreased product contamination. In this study two strategies toward synthesis of heterogeneous ruthenium-catalyst were explored using supported ionic liquid phase (SILP) and supported ionic liquid-like phase (SILLP) with multi-walled carbon nanotubes (MWCNTs) as a support. The structure of ionic liquids used for the construction of catalysts was varied regarding length of alkyl chain and anion in terms of providing influence on catalytic activity and stability as well as reaction product contamination. The activity of prepared catalysts was tested in ring-closing metathesis (RCM). The Ru-based SILLP catalyst demonstrated high performance (conversions >90 % in five reaction cycles), compared to SILP and Ru@MWCNTs catalyst synthesized using unmodified MWCNTs, additionally decreasing the product contamination with Ru (14 ppm).

Supported Ionic Liquid Phase Catalysts Dedicated for Continuous Flow Synthesis

Heterogeneous catalysis, although known for over a century, is constantly improved and plays a key role in solving the present problems in chemical technology. Thanks to the development of modern materials engineering, solid supports for catalytic phases having a highly developed surface are available. Recently, continuous-flow synthesis started to be a key technology in the synthesis of high added value chemicals. These processes are more efficient, sustainable, safer and cheaper to operate. The most promising is the use of heterogeneous catalyst with column-type fixed-bed reactors. The advantages of the use of heterogeneous catalyst in continuous flow reactors are the physical separation of product and catalyst, as well as the reduction in inactivation and loss of the catalyst. However, the state-of-the-art use of heterogeneous catalysts in flow systems compared to homogenous ones remains still open. The lifetime of heterogeneous catalysts remains a significant hurdle to realise sustainable flow synthesis. The goal of this review article was to present a state of knowledge concerning the application of Supported Ionic Liquid Phase (SILP) catalysts dedicated for continuous flow synthesis.

Effect of liquid confinement on regioselectivity in the hydrosilylation of alkynes with cationic Rh(I) N-heterocyclic carbene catalysts.

Polymeric mesoporous monoliths were prepared via ring-opening metathesis polymerization (ROMP) from norbornene (NBE), 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo,endo-dimethanonaphthalene (DMN-H6), tris(norborn-2-enylmethylenoxy)methylsilane and the 1st-generation Grubbs catalyst [RuCl2(PCy3)2(CHC6H5)] in the presence of 2-propanol and toluene and surface grafted with 1-(2-((norborn-5-ene-2-carbonyl)oxy)ethyl)-3-ethyl-1H-imidazol-3-ium tetrafluoroborate. Subsequently, a supported ionic-liquid-phase (SILP) system was created by immobilizing the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] with the cationic catalyst [Rh((1-pyrid-1-yl)-3-mesitylimidazol-2-ylidene)(COD)+BF4-] (Rh-1; COD = 1,4-cyclooctadiene) dissolved therein. The regio- and stereoselectivity of Rh-1 dissolved in the IL and supported on the mesoporous monolith, referred to as Rh@SILPROMP, in the hydrosilylation of 1-alkynes with HSiMe2Ph was studied and compared to that of the homogeneous catalyst Rh-1 under biphasic conditions using methyl tert-butyl ether (MTBE) as a second organic phase. Different amounts of IL were used, which allowed for the creation of SILPs with different layer thicknesses. Rh@SILPROMP provided by far better β-(Z) selectivity for both aromatic and aliphatic 1-alkynes in comparison to Rh-1 used under biphasic conditions. The highest β-(Z) selectivity was obtained with the thinnest IL layer. No leaching of the IL or rhodium from the SILP system into the organic phase was observed, resulting in virtually metal-free hydrosilylation products. The data obtained with Rh@SILPROMP were also compared with those from previous studies with Rh-1 in the same IL supported on polyurethane-derived mesoporous monolithic supports (Rh@SILPPUR) and on mesoporous SBA-15 (Rh@SILPSBA-15). For the first time, the use of a liquid confinement created by both a SILP and the support itself to tune the transition state of an organometallic catalyst by non-covalent interactions and thus stereo- and regioselectivity is outlined.

Wilkinson-type catalysts in ionic liquids for hydrogenation of small alkenes: understanding and improving catalyst stability

We apply supported ionic liquid phase (SILP) catalysts to hydrogenate small 1-alkenes in a continuous fixed-bed reactor. We rationalize the origin of catalyst decomposition via IR spectroscopy and adapt the catalyst design for improved stability.

SCILL-SILP hybrid catalytic system by employing carbon nanotubes as a support for the selective oxidation of ethylbenzene to acetophenone

Hydrocarbon oxidation to more valuable products is one of the most crucial industrial petrochemical processes. To improve efficiency, economic effectiveness, and reduction of waste production by conventional processes, the development of active and selective catalysts is still an important area of research. To cope with these challenges, we developed a catalytic system that utilized molecular oxygen to oxidize ethylbenzene (EB) to acetophenone (AcPO). The catalyst was prepared by coating a thin layer of a mixture of selected ionic liquid 1-ethyl-3-methylimidazolium octylsulfate and N-hydroxyphthalimide over industrial-grade multiwalled carbon nanotubes functionalized with copper(II) ions. This unique catalyst represented a hybrid catalytic system via the combination of solid catalyst with an ionic liquid layer (SCILL) and a supported ionic liquid phase (SILP) system. The oxidation reactions were performed at 80 °C and 0.1 MPa for 6 h. SCILL-SILP hybrid catalytic system exhibited exceptional performance with ∼27 % EB conversion and ∼77 % AcPO selectivity. The recyclability and reusability of the prepared catalysts were also investigated. The copper content was determined using inductively coupled plasma mass spectrometry (ICP-MS). Scanning electron microscopy (SEM) and transmission electron microscopy(TEM)were used to study the morphologies of the catalysts. Energy dispersive spectroscopy (EDS) was used to detect the immobilized copper on the functionalized CNTs while N2 physisorption analysis was employed to study the textural properties of the catalysts. Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to study the freshly synthesized and recycled catalysts.

The Buoy Effect: Surface Enrichment of a Pt Complex in IL Solution by Ligand Design.

The targeted enrichment of a Pt complex with an ionic liquid (IL)-derived ligand system in IL solution is demonstrated by using angle-resolved X-ray photoelectron spectroscopy. When the ligand system is complemented with fluorinated side chains, the complex accumulates strongly at the IL/gas interface, while in an equivalent solution of a complex without these substituents no such effect could be observed. This buoy-like behavior induces strong population of the complex at the outermost molecular layer close to surface saturation, which was studied over a range from 5 to 30 %mol . The surface enrichment was found to be most efficient at the lowest concentration, which is particularly favorable for catalytic applications such as supported ionic-liquid-phase (SILP) catalysis.

Supported ionic liquid phase facilitated catalysis with lipase from Aspergillus oryzae for enhance enantiomeric resolution of racemic ibuprofen

Supported ionic liquid phase (SILP) was used as a carrier for lipase from Aspergillus oryzae (LAO) and used as a biocatalyst for enantiomeric resolution of racemic ibuprofen via esterification leading to (S) -(+)-ibuprofen ester. Using native form of lipase, outstanding results were achieved, obtaining (S) -(+)-ibuprofen propyl ester with enantiomeric excess ( ee ) of 99.9% and high conversion of racemic ibuprofen after 24 h ( α = 34 . 8 % ) and respectively ee = 99.9% with α = 45 . 2 % after 48 h. Several hybrid materials composited with silica and metal-based oxides including magnesium, calcium, and zirconia were evaluated as supports for LAO with various surface characteristics. The selected ionic liquid 1-methyl-3-(triethoxysilylpropyl)imidazolium bis(trifluoromethylsulfonyl)imide was immobilized via the covalent bound onto the surface of solid material and in the second step LAO was anchored. Optimized results in enantiomeric resolution of racemic ibuprofen (35.23% conversion of rac -ibuprofen after 7 days with 95% ee of ester) were obtained for SILP biocatalyst based on MgO ⋅ SiO 2 (1:1) (ionic liquid loading 6.79%, enzyme loading 3.96%). This is proposed as a generic approach to tailoring supported ionic liquids phase biocatalysts for industrially-relevant reactions, to generate both environmentally and economically sustainable processes. • Aspergillus oryzae lipase was used in enantiomeric resolution of racemic ibuprofen. • Free enzyme showed over 45% reaction yield and 99.9% enantiomeric excess after 48 h. • Supported ionic liquid phase with lipase was used to improve system feasibility. • Modification of surface with ionic liquid enabled efficient immobilization of enzyme. • High reaction rate and enantioselectivity were maintained in the reusability test.