Organometallic complexes in supported ionic-liquid phase (SILP) catalysts: a PHIP NMR spectroscopy study

para-Hydrogen induced polarization (PHIP) NMR spectroscopy emerges as an efficient and robust method for on-line monitoring of gas-phase hydrogenation reactions. Here we report detailed investigations of supported ionic liquid phase (SILP) catalysts in a continuous gas-phase hydrogenation of propene with PHIP NMR spectroscopy. A relocation of the rhodium complex in the thin layer of ionic liquid in the SILP catalyst at the initial stage of the propene hydrogenation is demonstrated. PHIP NMR spectroscopy can provide profound insight into the evolution of SILP catalysts during hydrogenation reactions.     

A Dicationic Ruthenium Alkylidene Complex for Continuous Biphasic Metathesis Using Monolith‐Supported Ionic Liquids

A dicationic ruthenium–alkylidene complex [Ru(dmf)₃(IMesH₂)(?CH‐2‐(2‐PrO)‐C₆H₄)][(BF₄)₂] ( 1 ; IMesH₂=1,3‐dimesitylimidazolin‐2‐ylidene) has been prepared and used in continuous metathesis reactions by exploiting supported ionic‐liquid phase (SILP) technology. For these purposes, ring‐opening metathesis polymerization (ROMP)‐derived monoliths were prepared from norborn‐2‐ene, tris(norborn‐5‐ene‐2‐ylmethyloxy)methylsilane, and [RuCl₂(PCy₃)₂(CHPh)] (Cy=cyclohexyl) in the presence of 2‐propanol and toluene and surface grafted with norborn‐5‐en‐2‐ylmethyl‐N,N,N‐trimethylammonium tetrafluoroborate ([NBE‐CH₂‐NMe₃][BF₄]). Subsequent immobilization of the ionic liquid (IL), 1‐butyl‐2,3‐dimethylimidazolium tetrafluoroborate ([BDMIM][BF₄]), containing ionic catalyst 1 created the SILP catalyst. The use of a second liquid transport phase, which contained the substrate and was immiscible with the IL, allowed continuous metathesis reactions to be realized. High turnover numbers (TONs) of up to 3700 obtained in organic solvents for the ring‐closing metathesis (RCM) of, for example, N,N‐diallyltrifluoroacetamide, diethyl diallylmalonate, diethyl di(methallyl)malonate, tert‐butyl‐N,N‐diallylcarbamate, N,N‐diallylacetamide, diphenyldiallylsilane, and 1,7‐octadiene, as well as in the self‐metathesis of methyl oleate, could be further increased by using biphasic conditions with [BDMIM][BF₄]/heptane. Under continuous SILP conditions, TONs up to 900 were observed. Due to the ionic character of the initiator, catalyst leaching into the transport phase was very low (<0.1 %). Finally, the IL can, together with decomposed catalyst, be removed from the monolithic support by flushing with methanol. Upon reloading with [BDMIM][BF₄]/ 1 , the recycled support material again qualified for utilization in continuous metathesis reactions.     

Microwave Irradiation for the Facile Synthesis of Transition‐Metal Nanoparticles (NPs) in Ionic Liquids (ILs) from Metal–Carbonyl Precursors and Ru‐, Rh‐, and Ir‐NP/IL Dispersions as Biphasic Liquid–Liquid Hydrogenation Nanocatalysts for Cyclohexene

Stable chromium, molybdenum, tungsten, manganese, rhenium, ruthenium, osmium, cobalt, rhodium, and iridium metal nanoparticles (M‐NPs) have been reproducibly obtained by facile, rapid (3 min), and energy‐saving 10 W microwave irradiation (MWI) under an argon atmosphere from their metal–carbonyl precursors [M_x(CO)_y] in the ionic liquid (IL) 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIm][BF₄]). This MWI synthesis is compared to UV‐photolytic (1000 W, 15 min) or conventional thermal decomposition (180–250 °C, 6–12 h) of [M_x(CO)_y] in ILs. The MWI‐obtained nanoparticles have a very small (<5 nm) and uniform size and are prepared without any additional stabilizers or capping molecules as long‐term stable M‐NP/IL dispersions (characterization by transmission electron microscopy (TEM), transmission electron diffraction (TED), and dynamic light scattering (DLS)). The ruthenium, rhodium, or iridium nanoparticle/IL dispersions are highly active and easily recyclable catalysts for the biphasic liquid–liquid hydrogenation of cyclohexene to cyclohexane with activities of up to 522 (mol product) (mol Ru)^?1 h^?1 and 884 (mol product) (mol Rh)^?1 h^?1 and give almost quantitative conversion within 2 h at 10 bar H₂ and 90 °C. Catalyst poisoning experiments with CS₂ (0.05 equiv per Ru) suggest a heterogeneous surface catalysis of Ru‐NPs.     

Mechanism of the Water–Gas Shift Reaction Catalyzed by Efficient Ruthenium‐Based Catalysts: A Computational and Experimental Study

Supported ionic liquid phase (SILP) catalysis enables a highly efficient, Ru‐based, homogeneously catalyzed water‐gas shift reaction (WGSR) between 100 °C and 150 °C. The active Ru‐complexes have been found to exist in imidazolium chloride melts under operating conditions in a dynamic equilibrium, which is dominated by the [Ru(CO)₃Cl₃]^? complex. Herein we present state‐of‐the‐art theoretical calculations to elucidate the reaction mechanism in more detail. We show that the mechanism includes the intermediate formation and degradation of hydrogen chloride, which effectively reduces the high barrier for the formation of the requisite dihydrogen complex. The hypothesis that the rate‐limiting step involves water is supported by using D₂O in continuous catalytic WGSR experiments. The resulting mechanism constitutes a highly competitive alternative to earlier reported generic routes involving nucleophilic addition of hydroxide in the gas phase and in solution.     

First application of supported ionic liquid phase (SILP) catalysis for continuous methanol carbonylation

A solid, silica-supported ionic liquid phase (SILP) rhodium iodide Monsanto-type catalyst system, [BMIM][Rh(CO)2I2]-[BMIM]I-SiO2, exhibits excellent activity and selectivity towards acetyl products in fixed-bed, continuous gas-phase methanol carbonylation.     

MoP Nanoparticles Supported on Indium‐Doped Porous Carbon: Outstanding Catalysts for Highly Efficient CO2 Electroreduction

Electrochemical reduction of CO₂ into value‐added product is an interesting area. MoP nanoparticles supported on porous carbon were synthesized using metal–organic frameworks as the carbon precursor, and initial work on CO₂ electroreduction using the MoP‐based catalyst were carried out. It was discovered that MoP nanoparticles supported on In‐doped porous carbon had outstanding performance for CO₂ reduction to formic acid. The Faradaic efficiency and current density could reach 96.5 % and 43.8 mA cm^?2, respectively, when using ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate as the supporting electrolyte. The current density is higher than those reported up to date with very high Faradaic efficiency. The MoP nanoparticles and the doped In₂O₃ cooperated very well in catalyzing the CO₂ electroreduction.     

Catalytic polymerization of phenylacetylene with dimeric [Rh(OMe)(cod)]2 complex in ionic liquids

Dimeric rhodium(I) complex [Rh(OMe)(cod)]₂ was found to be an active catalyst of phenylacetylene polymerization to poly(phenylacetylene) (PPA) in ionic liquids containing imidazolium or pyridinium cations. The highest yield of PPA (92%) was obtained in 1‐butyl‐4‐methylpyridinium tetrafluoroborate as reaction medium. The yield of PPA in imidazolium ionic liquids containing BF₄^? or PF₆^? anions increased to 83–99% when Et₃N or cycloocta‐1,5‐diene were added as co‐catalysts. In 1‐methyl‐3‐octylimidazolium chloride (MOI · Cl) polymerization rate was much lower than in other ionic liquids, although the highest M_w (72 400) was obtained. Spectroscopic studies confirmed that [Rh(OMe)(cod)]₂ reacted with MOI · Cl forming new carbene Rh(I) complex, which can participate in the polymerization process. Copyright © 2006 John Wiley & Sons, Ltd.     

Development of a Continuous‐Flow System for Asymmetric Hydrogenation Using Self‐Supported Chiral Catalysts

Well‐designed, self‐assembled, metal–organic frameworks were constructed by simple mixing of multitopic MonoPhos‐based ligands ( 3 ; MonoPhos=chiral, monodentate phosphoramidites based on the 1,1′‐bi‐2‐naphthol platform) and [Rh(cod)₂]BF₄ (cod=cycloocta‐1,5‐diene). This self‐supporting strategy allowed for simple and efficient catalyst immobilization without the use of extra added support, giving well‐characterized, insoluble (in toluene) polymeric materials ( 4 ). The resulting self‐supported catalysts ( 4 ) showed outstanding catalytic performance for the asymmetric hydrogenation of a number of α‐dehydroamino acids ( 5 ) and 2‐aryl enamides ( 7 ) with enantiomeric excess (ee) ranges of 94–98 % and 90–98 %, respectively. The linker moiety in 4 influenced the reactivity significantly, albeit with slight impact on the enantioselectivity. Acquisition of reaction profiles under steady‐state conditions showed 4 h and 4 i to have the highest reactivity (turnover frequency (TOF)=95 and 97 h^?1 at 2 atm, respectively), whereas appropriate substrate/catalyst matching was needed for optimum chiral induction. The former was recycled 10 times without loss in ee (95–96 %), although a drop in TOF of approximately 20 % per cycle was observed. The estimation of effective catalytic sites in self‐supported catalyst 4 e was also carried out by isolation and hydrogenation of catalyst–substrate complex, showing about 37 % of the Rh^I centers in the self‐supported catalyst 4 e are accessible to substrate 5 c in the catalysis. A continuous flow reaction system using an activated C/ 4 h mixture as stationary‐phase catalyst for the asymmetric hydrogenation of 5 b was developed and run continuously for a total of 144 h with >99 % conversion and 96–97 % enantioselectivity. The total Rh leaching in the product solution is 1.7 % of that in original catalyst 4 h .     

A Mixed‐Ligand Chiral Rhodium(II) Catalyst Enables the Enantioselective Total Synthesis of Piperarborenine B

A novel, mixed‐ligand chiral rhodium(II) catalyst, Rh₂(S‐NTTL)₃(dCPA), has enabled the first enantioselective total synthesis of the natural product piperarborenine B. A crystal structure of Rh₂(S‐NTTL)₃(dCPA) reveals a “chiral crown” conformation with a bulky dicyclohexylphenyl acetate ligand and three N‐naphthalimido groups oriented on the same face of the catalyst. The natural product was prepared on large scale using rhodium‐catalyzed bicyclobutanation/ copper‐catalyzed homoconjugate addition chemistry in the key step. The route proceeds in ten steps with an 8 % overall yield and 92 % ee.     

离子液体催化剂用于煤焦化苯深度脱硫制无硫苯

从扩大有机合成用苯的需求出发,采用研制的离子液体催化剂考察了煤焦化苯深度脱硫制无硫苯的过程。结果表明：N-甲基咪唑硫酸氢盐[Hmim][HSO₄]离子液体催化剂脱噻吩效果与其酸函数值有关。本文采用Hammett指示剂测定离子液体的酸函数H₀,并得出：在-4至-12的范围,离子液体催化剂可以使煤焦化苯噻吩脱至0. 5mg/L以下。与固体酸催化机理相似,酸量和酸强度一定的离子液体催化剂通过Friedel-Crafts反应形成烷基噻吩等,与苯的物性拉开距离,对苯的分离精制是必不可少的,但是过多、过强的[Hmim][HSO₄]酸值也更有利于苯-噻吩-烯烃共聚合等副反应的发生,从而影响离子液体催化剂重复使用的寿命。本研究利用煤焦化苯脱硫反应形成的噻吩衍生物作为提供电荷流通的聚合物,将反复使用后性能不佳的离子液体成分等作为“受电子型”和“给电子型”的掺杂剂,进行导电（抗静电）材料的制备。结果显示：对煤焦化苯脱硫形成的噻吩衍生物等可以用于掺杂导电材料的试制。     

Removal of Multiple Contaminants from Water by Polyoxometalate Supported Ionic Liquid Phases (POM‐SILPs)

The simultaneous removal of organic, inorganic, and microbial contaminants from water by one material offers significant advantages when fast, facile, and robust water purification is required. Herein, we present a supported ionic liquid phase (SILP) composite where each component targets a specific type of water contaminant: a polyoxometalate‐ionic liquid (POM‐IL) is immobilized on porous silica, giving the heterogeneous SILP. The water‐insoluble POM‐IL is composed of antimicrobial alkylammonium cations and lacunary polyoxometalate anions with heavy‐metal binding sites. The lipophilicity of the POM‐IL enables adsorption of organic contaminants. The silica support can bind radionuclides. Using the POM‐SILP in filtration columns enables one‐step multi‐contaminant water purification. The results show how multi‐functional POM‐SILPs can be designed for advanced purification applications.     

Heck Reaction of Iodoarenes with Methyl Acrylate Catalyzed by Cyciopalladated Complexes of Tertiary Arylamines Immobilized in Ionic Liquid[ Bmim ] ^＋ BF4^-

Heck reaction of iodoarenes with methyl acrylate, catalyzed by cyclolmlladated complexes of tertiary arylamines, was investi-gated in ionic liquid 1-butyl-3-metylimidazolium tetratluorobo-rate ([Bmim] BF4^- ). The products can be isolated convenient-ly from the ionic liquid-catalyst system. The catalysts could be reused for more than 10 times still with satisfactory catalytic ac-tivity.     

Hollow Metal–Organic‐Framework‐Mediated In Situ Architecture of Copper Dendrites for Enhanced CO2 Electroreduction

Electrocatalytic reduction of CO₂ to a single product at high current densities and efficiencies remains a challenge. However, the conventional electrode preparation methods, such as drop‐casting, usually suffer from low intrinsic activity. Herein, we report a synthesis strategy for preparing heterogeneous electrocatalyst composed of 3D hierarchical Cu dendrites that derived from an in situ electrosynthesized hollow copper metal–organic framework (MOF), for which the preparation of the Cu‐MOF film took only 5 min. The synthesis strategy preferentially exposes active sites, which favor's the reduction of CO₂ to formate. The current density could be as high as 102.1 mA cm^?2 with a selectivity of 98.2 % in ionic‐liquid‐based electrolyte and a commonly used H‐type cell.     

Cooperative Effects in Catalytic Hydrogenation Regulated by both the Cation and Anion of an Ionic Liquid

The use of transition‐metal nanoparticles/ionic liquid (IL) as a thermoregulated and recyclable catalytic system for hydrogenation has been investigated under mild conditions. The functionalized ionic liquid was composed of poly(ethylene glycol)‐functionalized alkylimidazolium as the cation and tris(meta‐sulfonatophenyl)phosphine ([P(C₆H₄‐m‐SO₃)₃]^3?) as the anion. Ethyl acetate was chosen as the thermomorphic solvent to avoid the use of toxic organic solvents. Due to a cooperative effect regulated by both the cation and anion of the ionic liquid, the nanocatalysts displayed distinguished temperature‐dependent phase behavior and excellent catalytic activity and selectivity, coupled with high stability. In the hydrogenation of α,β‐unsaturated aldehydes, the ionic‐liquid‐stabilized palladium and rhodium nanoparticles exhibited higher selectivity for the hydrogenation of the C?C bonds than commercially available catalysts (Pd/C and Rh/C). We believe that the anion of the ionic liquid, [P(C₆H₄‐m‐SO₃)₃]^3?, plays a role in changing the surrounding electronic characteristics of the nanoparticles through its coordination capacity, whereas the poly(ethylene glycol)‐functionalized alkylimidazolium cation is responsible for the thermomorphic properties of the nanocatalyst in ethyl acetate. The present catalytic systems can be employed for the hydrogenation of a wide range of substrates bearing different functional groups. The catalysts could be easily separated from the products by thermoregulated phase separation and efficiently recycled ten times without significant changes in their catalytic activity.     

Water‐in‐Supercritical CO2 Microemulsion Stabilized by a Metal Complex

Herein we propose for the first time the utilization of a metal complex for forming water‐in‐supercritical CO₂ (scCO₂) microemulsions. The water solubility in the metal‐complex‐stabilized microemulsion is significantly improved compared with the conventional water‐in‐scCO₂ microemulsions stabilized by hydrocarbons. Such a microemulsion provides a promising route for the in situ CO₂ reduction catalyzed by a metal complex at the water/scCO₂ interface.     

Characterization of Supported Ionic Liquid Phase (SILP) materials prepared from different supports

Supported ionic liquid phase (SILP) materials are a recent concept where a film of ionic liquid (IL) is immobilized on a solid phase, combining the advantages of ILs (non volatility, high solvent capacity, etc.) with those of heterogeneous support materials. In this work, new SILP materials were prepared using a series of supports with different porosity and chemical nature. An imidazolium-based IL, 1-methyl-3-octylimidazolium hexafluorophosphate (OmimPF₆), was confined at variable contents (5–60% w/w) in three different activated carbons (ACs), silica (SiO₂), alumina (Al₂O₃) and titania (TiO₂).     

Understanding the Buoy Effect of Surface-Enriched Pt Complexes in Ionic Liquids: A Combined ARXPS and Pendant Drop Study**

Recently, we demonstrated that Pt catalyst complexes dissolved in the ionic liquid (IL) [C₄C₁Im][PF₆] can be deliberately enriched at the IL surface by introducing perfluorinated substituents, which act like buoys dragging the metal complex towards the surface. Herein, we extend our previous angle-resolved X-ray photoelectron spectroscopy (ARXPS) studies at complex concentrations between 30 and 5 %_mol down to 1 %_mol and present complementary surface tension pendant drop (PD) measurements under ultraclean vacuum conditions. This combination allows for connecting the microscopic information on the IL/gas interface derived from ARXPS with the macroscopic property surface tension. The surface enrichment of the Pt complexes is found to be most pronounced at 1 %_mol. It also displays a strong temperature dependence, which was not observed for 5 %_mol and above, where the surface is already saturated with the complex. The surface enrichment deduced from ARXPS is also reflected by the pronounced decrease in surface tension with increasing concentration of the catalyst. We furthermore observe by ARXPS and PD a much stronger surface affinity of the buoy-complex as compared to the free ligands in solution. Our results are highly interesting for an optimum design of IL-based catalyst systems with large contact areas to the surrounding reactant/product phase, such as in supported IL phase (SILP) catalysis.     

Water Purification and Microplastics Removal Using Magnetic Polyoxometalate‐Supported Ionic Liquid Phases (magPOM‐SILPs)

Filtration is an established water‐purification technology. However, due to low flow rates, the filtration of large volumes of water is often not practical. Herein, we report an alternative purification approach in which a magnetic nanoparticle composite is used to remove organic, inorganic, microbial, and microplastics pollutants from water. The composite is based on a polyoxometalate ionic liquid (POM‐IL) adsorbed onto magnetic microporous core–shell Fe₂O₃/SiO₂ particles, giving a magnetic POM‐supported ionic liquid phase (magPOM‐SILP). Efficient, often quantitative removal of several typical surface water pollutants is reported together with facile removal of the particles using a permanent magnet. Tuning of the composite components could lead to new materials for centralized and decentralized water purification systems.     

A Monolithic Hybrid Cellulose‐2.5‐Acetate/Polymer Bioreactor for Biocatalysis under Continuous Liquid–Liquid Conditions Using a Supported Ionic Liquid Phase

Mesoporous monolithic hybrid cellulose‐2.5‐acetate (CA)/polymer supports were prepared under solvent‐induced phase separation conditions using cellulose‐2.5‐acetate microbeads 8–14 μm in diameter, 1,1,1‐tris(hydroxymethyl)propane and 4,4′‐methylenebis(phenylisocyanate) as monomers as well as THF and n‐heptane as porogenic solvents. 4‐(Dimethylamino)pyridine and dibutyltin dilaurate (DBTDL), respectively, were used as catalysts. Monolithic hybrid supports were used in transesterification reactions of vinyl butyrate with 1‐butanol under continuous, supported ionic liquid–liquid conditions with Candida antarctica lipase B (CALB) and octylmethylimidazolium tetrafluoroborate ([OMIM⁺][BF₄^?]) immobilized within the CA beads inside the polymeric monolithic framework and methyl tert‐butyl ether (MTBE) as the continuous phase. The new hybrid bioreactors were successfully used in dimensions up to 2×30 cm (V=94 mL). Under continuous biphasic liquid–liquid conditions a constant conversion up to 96 % was achieved over a period of 18 days, resulting in a productivity of 58 μmol mg^?1(CALB) min^?1. This translates into an unprecedented turnover number (TON) of 3.9×10⁷ within two weeks, which is much higher than the one obtained under standard biphasic conditions using [OMIM⁺][BF₄^?]/MTBE (TON=2.7×10⁶). The continuous liquid–liquid setup based on a hybrid reactor presented here is strongly believed to be applicable to many other enzyme‐catalyzed reactions.     

Adding magnetic ionic liquid monomers to the emulsion polymerization tool‐box: Towards polymer latexes and coatings with new properties

Magnetic ionic liquid monomers were synthesized and then polymerized to get magnetic polymer latexes and films. First, a series of 1‐vinyl‐3‐dodecyl‐imidazolium monomers having metal halides counter‐anions such as FeCl₃Br^?, CoCl₂Br^?, and MnCl₂Br^? were synthesized. These ionic liquid monomers were first homopolymerized to lead to magnetic poly(ionic liquids) and characterized. Secondly, magnetic latexes were synthesized by using the magnetic ionic liquids as surfmers (surfactant + monomer) in the emulsion polymerization of methyl methacrylate/n‐butyl acrylate. It was found that the powders obtained by freeze‐drying the latexes presented a paramagnetic behavior with weak antiferromagnetic interactions between the adjacent metal ions. Although the ratio of magnetic ionic liquid/monomer was only 2% these poly(methyl methacrylate‐co‐butyl acrylate) powders and latexes responded to a magnetic field due to the surfmer paramagnetic nature. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1145–1152