This work was supported by the Florida State University Energy and Materials Hiring initiative and the FSU Department of Chemical and Biomedical Engineering.

Note: We presented the synthesis of 4-(97-(adamantan-1-yloxy)-2,5,8,11,14,17,20,23,26,29,32,35,38,41,44,47,50,53,56,59,62,65,68,71,74,77,80,83,86,89,92,95-dotriacontaoxaheptanonacontyl)-1,3-dimesityl-4,5-dihydro-1H-imidazol-3-ium tetrafluoroborate (imidazolium salt A) and host complex, &#946;-CD grafted silica, in our previous paper38. In the protocol, we describe a synthesis of our water-soluble Ru olefin metathesis catalyst and metathesis reactions (RCM and ROMP).
1. Synthesis of (4-(97-((adamantan-1-yl)oxy)-2,5,8,11,14,17,20,23,26,29,32,35,38,41,44,47,50,53,56,59,62,65,68,71,74,77,80,83,86,89,92,95-dotriacontaoxaheptanonacontyl)-1,3-dimesitylimidazolidinylidene)dichloro( o -isopropoxyphenylmethylene)ruthenium (Catalyst 1)
<ol>
	<li>Dry a 25 mL round-bottomed flask with a stirring bar, a 20 mL vial, and a spatula in oven.</li>
	<li>Put 118 mg of imidazolium salt A (0.060 mmol) in a 4 mL vial.</li>
	<li>Place the prepared imidazolium salt A in dried glassware, a septum and the spatula in a glove box chamber and vacuum for 2 h.</li>
	<li>After completely removing the air in glove box chamber, purge the inert gas into the chamber, then move them into the glove box.</li>
	<li>In the glove box, put 54 mg of Hoveyda-Grubbs (H-G) 1st generation (0.090 mmol, 1.5 equiv.) in a 20 mL vial.</li>
	<li>Dissolve the prepared imidazolium salt in 2.0 mL of toluene, then transfer it into the 50 mL round-bottomed flask with the stirring bar.</li>
	<li>Add 0.18 mL of potassium bis(trimethylsilyl)amide (KHMDS) solution (0.5 M toluene solution, 0.090 mmol, 1.5 equiv.) into the imidazolium salt solution.</li>
	<li>Swirl the flask to mix the reagents.</li>
	<li>Dissolve the H-G 1st generation in 3.0 mL of toluene, then add this solution into the reaction flask.</li>
	<li>Seal the flask with septum, then remove this from the glove box.</li>
	<li>Stir the reaction mixture for 3 h at 80 &#176;C.</li>
	<li>After 3 h, purify the catalyst by chromatography on neutral alumina, eluted with EtOAc/MeOH = 15/1. Collect the dark green solution. 
	Note: Evaporation of the solvent is not required before chromatography. Rf value is 0.46 on neutral alumina, eluted with EtOAc/MeOH = 15/1.</li>
	<li>Remove the solvent under reduced pressure.</li>
	<li>Vacuum the final residue to obtain dark green waxy solid.</li>
</ol>
2. Metathesis Reaction and Removal of Catalyst Residue in Aqueous Media
<ol>
	<li>Prepare degassed deuterium oxide (D2O) or deionized water by bubbling D2O or deionized water with nitrogen gas over 2 h.</li>
	<li>Put 4.4 mg of the catalyst 1 (0.0020 mmol) and 41 mg of 2-allyl-N,N,N-trimethylpent-4-en-1-aminium chloride (tetraalkyl ammonium substrate) (0.20 mmol) in each 4.0 mL vial.</li>
	<li>Dissolve the tetraalkyl ammonium substrate in 0.5 mL of degassed D2O (or H2O), then add the solution into catalyst 1.</li>
	<li>Seal the reaction vial, then heat the reaction mixture for 24 h at 45 &#176;C. Monitor the reaction conversion by 1H NMR. 
	NOTE: Monitor the 1H NMR peak conversion from 3.25 ppm (doublet, -NCH2CH- in substrate) to 3.52 ppm (doublet, -NCH2CH- in product).</li>
	<li>After the completion of the reaction, cool down the reaction vial at room temperature.</li>
	<li>Add 150 mg of &#946;-CD grafted silica into the reaction mixture. 
	Note: Grafted &#946;-CD unit onto the silica gel was calculated in 1.57 10-4 mmol/mg by thermogravimetric analysis (TGA).</li>
	<li>Stir the reaction mixture for 10 h at room temperature.</li>
	<li>Filter the reaction mixture through cotton plug.</li>
	<li>Remove the solvent in a freeze dryer.</li>
</ol>
3. Ring-opening Metathesis Polymerization and Removal of Catalyst Residue in Aqueous Media
<ol>
	<li>Prepare degassed D2O or deionized water by bubbling D2O or deionized water with nitrogen gas over 2 h.</li>
	<li>Put 4.4 mg of the catalyst 1 (0.0020 mmol) and 17.1 mg of 2-((3aR*,4S*,7R*,7aS*)-1,3-dioxo-1,3,3a,4,7,7a-hexahydro-2H-4,7-methanoisoindol-2-yl)-N,N,N-trimethylethan-1-aminium chloride (monomer, Figure 5) (0.060 mmol) in each 4.0 mL vial.</li>
	<li>Dissolve the monomer in 0.5 mL of degassed D2O (or H2O), then add the solution into catalyst 1.</li>
	<li>Seal the reaction vial, then heat the reaction mixture for 2 h at 45 &#176;C. Monitor the reaction conversion by 1H NMR. 
	NOTE: Monitor the 1H NMR peak disappearance at 6.14 ppm (-CH=CH- in monomer).</li>
	<li>After the completion of the reaction, cool down the reaction vial at room temperature.</li>
	<li>Quench the reaction with 0.1 mL of ethyl vinyl ether. 
	Note: Quenching is necessary to dissociate Ru catalyst from polymer chain terminal.</li>
	<li>Add 150 mg of &#946;-CD grafted silica into the reaction mixture.</li>
	<li>Stir the reaction mixture for 10 h at room temperature.</li>
	<li>Filter the reaction mixture through cotton plug.</li>
	<li>Remove the solvent in a freeze dryer.</li>
</ol>
4. Metathesis Reaction and Removal of Catalyst Residue from CH2Cl2
<ol>
	<li>Put 4.4 mg of the catalyst 1 (0.0020 mmol) and 48 mg of diethyl diallylmalonate (0.20 mmol) in each 4.0 mL vial.</li>
	<li>Dissolve the diethyl diallylmalonate in 0.5 mL of CH2Cl2, then add the solution into catalyst 1.</li>
	<li>Seal the reaction vial, then keep the reaction mixture at room temperature for 1 h. Monitor the reaction conversion by 1H NMR. 
	Note: Monitor the 1H NMR peak conversion from 2.63 ppm (doublet, -CCH2CH=CH2 in substrate) to 3.01 ppm (singlet, -CCH2CH=CHCH2C- in product).</li>
	<li>After the completion of the reaction, transfer the resulting reaction mixture into a 30 mL vial.</li>
	<li>Dilute the reaction solution with 15 mL of diethyl ether.</li>
	<li>Wash the organic solution with 15 mL of water for five times.</li>
	<li>Dry the organic layer with MgSO4, then filter the solution through cotton plug to remove MgSO4 particles.</li>
	<li>Add 60 mg of activated carbon into the resulting solution, then stir the mixture for 24 h at room temperature.</li>
	<li>Filter the solution through cotton plug to remove activated carbon, then remove the solvent under reduced pressure.</li>
</ol>

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The authors declare no competing financial interest.

We described the synthesis of removable homogeneous Ru olefin metathesis catalyst and its removal from both aqueous and organic solutions. Homogeneous catalysis provides many benefits compared to heterogeneous catalysts, such as high reactivity and rapid reaction rate; however, the removal of the used catalyst from the product is more difficult than heterogeneous catalyst3. The key feature of synthesized catalyst is the NHC ligand, which bears adamantyl tethered water soluble oligo(ethylene glycol...

The removal of the homogeneous organometallic catalysis from the product is an important issue in modern chemistry1,2. Residual catalyst causes not only a toxicity problem from its heavy metal element, but also an undesired transformation of product from its potential reactivity. Homogeneous catalyst provides many advantages, such as high activity, rapid reaction rate, and chemoselectivity3, however, its removal from the product is much more difficult than heterogeneous catalyst which is simply removed by filtration or decantation. The combination of the advantages of homogeneous and heterogeneous catalyst, i.e., homogeneous reaction and heterogeneous removal, represents important concept for highly reactive and easily removable organometallic catalyst. Figure 1 illustrated the working principle for homogeneous reaction and heterogeneous removal of the catalyst via host-guest interaction.
Host-guest chemistry is noncovalent bonding molecular recognition between host molecules and guest molecules in supramolecular chemistry4,5,6,7,8. Cyclodextrins (CDs), cyclic oligosaccharides, are representative host molecules9,10,11,12, and they have been applied in broad fields of science such as, polymer science13,14, catalysis15,16, biomedical applications6,10, and analytical chemistry17. A guest molecule, adamatane, binds strongly to the hydrophobic cavity of &#946;-CD (host, 7-membered cyclic saccharide) with high association constant, Ka (log Ka = 5.04)18. This supramolecular binding affinity is strong enough to remove residual catalyst complex from the aqueous reaction solution with solid supported &#946;-CD.
Among many catalysts that are eligible for the host-guest removal, Ru olefin metathesis catalyst was studied due to high practical utilities and high stability against air and moisture. The olefin metathesis reaction is an important tool in synthetic chemistry to form a carbon-carbon double bond in the presence of a transition metal catalyst19,20,21,22. The development of stable Ru olefin metathesis catalyst trigged the metathesis as a major field in synthetic chemistry (e.g., RCM and cross metathesis (CM)) as well as polymer science (e.g., ROMP and acyclic diene metathesis (ADMET)). In particular, the RCM synthesizes macrocycles and medium-sized rings that have been hard to construct23.
In spite of synthetic utilities of Ru catalyzed olefin metathesis, complete removal of used Ru catalyst from the desired product is a major challenge for many practical applications24. For example, 1912 ppm of Ru residue was observed in ring-closing metathesis product after silica gel column chromatography25. Residual Ru may cause problems such as olefin isomerization, decomposition, colorization, and toxicity of pharmaceutical products26. International Conference on Harmonization (ICH) published a guideline of residual metal reagents in pharmaceuticals. The maximum allowed Ru level in pharmaceutical product is 10 ppm27. For these reasons, various approaches were tried to remove Ru residue from the product solution28,29,30,31,32,33. Also, the developments of removable Ru catalysts have been studied for purification without any special treatment after the reaction. Among various purification methods, catalyst ligand modifications were tried to improve efficiency of silica gel filtration and liquid extraction. For example, highly efficient silica gel filtration can be achieved by introduced ion tag on benzylidene34 or backbone of NHC ligand35,36. The catalyst bearing poly(ethylene glycol)37 or ion tag35 on a NHC ligand can improve the efficiency of aqueous extraction for Ru catalyst removal.
Recently, we reported a highly water soluble Ru olefin metathesis catalyst, which demonstrated not only high reactivity, but also high catalyst removal rate. Moreover, the metathesis and catalyst removal occurred in both water and dichloromethane34,35,36,37. The key feature of new catalyst is that the new NHC bears adamantyl tethered oligo(ethylene glycol). Oligo(ethylene glycol) provides high water solubility of the entire catalyst complex. In addition, the oligo(ethylene glycol) possesses adamantyl end group that can be used in host-guest interaction with external &#946;-CD.
Herein, we described the protocols for catalyst synthesis, metathesis reactions, and catalyst removal in both water and dichloromethane.

<table><tbody><tr><td>Hoveyda-Grubbs Catalyst 1st Generation</td><td>Sigma-Aldrich</td><td>577944</td><td>Air sensitivie. Light sensitivie.</td></tr><tr><td>Diethyl diallylmalonate</td><td>Sigma-Aldrich</td><td>283479</td><td></td></tr><tr><td>Ethyl vinyl ether</td><td>Sigma-Aldrich</td><td>422177</td><td>Air sensitive.</td></tr><tr><td>Aluminum oxide</td><td>Sigma-Aldrich</td><td>06300</td><td>Activated, neutral, Brockmann Activity I</td></tr><tr><td>Potassium bis(trimethylsilyl)amide solution (0.5 M in toluene)</td><td>Sigma-Aldrich</td><td>277304</td><td>Moisture sensitive.</td></tr><tr><td>Etyhl acetate</td><td>VWR</td><td>BDH1123</td><td>Flammable liquid.</td></tr><tr><td>Methanol</td><td>VWR</td><td>BDH1135</td><td>Flammable liquid. Toxic.</td></tr><tr><td>Deuterium Oxide 99.8%D</td><td>TCI</td><td>W0002</td><td></td></tr><tr><td>Methylene Chloride-D2 (D, 99.8%)</td><td>Cambridge Isotope Laboratories, Inc.</td><td>DLM-23</td><td>Flammable liquid. Toxic.</td></tr><tr><td>Activated carbon</td><td>Sigma-Aldrich</td><td>242276</td><td></td></tr><tr><td>Magnesium sulfate</td><td>EMD Millipore</td><td>MX0075</td><td></td></tr><tr><td>Ethyl ether</td><td>EMD Millipore</td><td>EX0190</td><td>Flammable liquid.</td></tr></tbody></table>

heterogeneous removal of water-soluble ruthenium olefin metathesis catalyst from aqueous media via host-guest interaction

A highly efficient transition metal catalyst removal method is developed. The water-soluble catalyst contains a newly-designed NHC ligand for the catalyst removal via host-guest interactions. The new NHC ligand possesses an adamantyl (guest) tethered linear ethylene glycol units for hydrophobic inclusion into the cavity of a &#946;-cyclodextrin (&#946;-CD) host compound. The new NHC ligand was applied to a Ru-based olefin metathesis catalyst. The Ru catalyst demonstrated excellent activity in representative ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions in aqueous media as well as organic solvent, CH2Cl2. After the reaction was complete, the lingering Ru residue was removed from the aqueous solution with the efficiency of more than 99% (53 ppm of Ru residue) by simple filtration utilizing a host-guest interaction between insoluble silica-grafted &#946;-CD (host) and the adamantyl moiety (guest) on the catalyst. The new Ru catalyst also demonstrated high removal efficiency via extraction when the reaction is run in organic solvent by partitioning the crude reaction mixture between layers of diethyl ether and water. In this way, the catalyst stays in aqueous layer only. In organic layer, the residual Ru amount was only 0.14 ppm in the RCM reactions of diallyl compounds.

Figure 2&#160;describes the ligand exchange reaction for our catalyst 1. The 1H NMR spectrum is shown in Figure 3.
Figure 4&#160;shows the RCM in aqueous solution and subsequent removal of used catalyst from the reaction mixture via host-guest interaction, and Table 1 summarizes RCM in aqueous me...

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Heterogeneous Removal of Water-Soluble Ruthenium Olefin Metathesis Catalyst from Aqueous Media Via Host-Guest Interaction

A removable water-soluble N-heterocyclic carbene (NHC) ligand in aqueous media via host-guest interaction has been developed. We demonstrated representative olefin metathesis reactions in water as well as in dichloromethane. Via either host-guest interaction or extraction, the residual ruthenium (Ru) catalyst was as low as 0.14 ppm after the reaction.

A highly efficient transition metal catalyst removal method is developed. The water-soluble catalyst contains a newly-designed NHC ligand for the catalyst ...

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7.8K Views.  Florida State University. Een verwisselbare wateroplosbare N-heterocyclische carbeen (NHC) ligand in waterige media via host-guest interactie heeft ontwikkeld. We toonden de representatieve olefine Metathese reacties in water zo goed zoals in dichloormethaan. Via de host-guest interactie of extractie werd de residuele ruthenium (Ru)-katalysator zo laag als 0,14 ppm na de reactie.

Video: Heterogeneous Removal of Water-Soluble Ruthenium Olefin Metathesis Catalyst from Aqueous Media Via Host-Guest Interaction

Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium Under Mild Reaction Conditions

Dichloro-bis(aminophosphine) complexes of palladium with the general formula of [(P{(NC5H10)3-n(C6H11)n})2Pd(Cl)2] (where n = 0-2), belong to a new family of easy accessible, very cheap, and air stable, but highly active and universally applicable C-C cross-coupling catalysts with an excellent functional group tolerance. Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium [(P(NC5H10)3)2Pd(Cl)2] (1), the least stable complex within this series towards protons; e.g. in the form of water, allows an eased nanoparticle formation and hence, proved to be the most active Heck catalyst within this series at 100 &#176;C and is a very rare example of an effective and versatile catalyst system that efficiently operates under mild reaction conditions. Rapid and complete catalyst degradation under work-up conditions into phosphonates, piperidinium salts and other, palladium-containing decomposition products assure an easy separation of the coupling products from catalyst and ligands. The facile, cheap, and rapid synthesis of 1,1',1"-(phosphinetriyl)tripiperidine and 1 respectively, the simple and convenient use as well as its excellent catalytic performance in the Heck reaction at 100 &#176;C make 1 to one of the most attractive and greenest Heck catalysts available.
We provide here the visualized protocols for the ligand and catalyst syntheses as well as the reaction protocol for Heck reactions performed at 10 mmol scale at 100 &#176;C and show that this catalyst is suitable for its use in organic syntheses.

Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-phosphinetriyltripiperidine]}palladium Under Mild Reaction Conditions

Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium [(P(NC5H10)3)2Pd(Cl)2] (1) is an easy accessible, cheap, and air stable, but highly active Heck catalyst with an excellent functional group tolerance that efficiently operates under mild reaction conditions to give the coupling products in very high yields.

Dichloro-bis(aminophosphine) complexes of palladium with the general formula of [(P{(NC5H10)3-n(C6H11)n})2Pd(Cl)2] (where n = 0-2), belong to a new family ...

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Herein we report the synthesis of a tridentate phosphine ligand N(CH2PPh2)3 (N-triphosPh) (1) via a phosphorus based Mannich reaction of the hydroxylmethylene phosphine precursor with ammonia in methanol under a nitrogen atmosphere. The N-triphosPh ligand precipitates from the solution after approximately 1 hr of reflux and can be isolated analytically pure via simple cannula filtration procedure under nitrogen. Reaction of the N-triphosPh ligand with [Ru3(CO)12] under reflux affords a deep red solution that show evolution of CO gas on ligand complexation. Orange crystals of the complex [Ru(CO)2{N(CH2PPh2)3}-&#954;3P] (2) were isolated on cooling to RT. The 31P{1H} NMR spectrum showed a characteristic single peak at lower frequency compared to the free ligand. Reaction of a toluene solution of complex 2 with oxygen resulted in the instantaneous precipitation of the carbonate complex [Ru(CO3)(CO){N(CH2PPh2)3}-&#954;3P] (3) as an air stable orange solid. Subsequent hydrogenation of 3 under 15 bar of hydrogen in a high-pressure reactor gave the dihydride complex [RuH2(CO){N(CH2PPh2)3}-&#954;3P] (4), which was fully characterized by X-ray crystallography and NMR spectroscopy. Complexes 3 and 4 are potentially useful catalyst precursors for a range of hydrogenation reactions, including biomass-derived products such as levulinic acid (LA). Complex 4 was found to cleanly react with LA in the presence of the proton source additive NH4PF6 to give [Ru(CO){N(CH2PPh2)3}-&#954;3P{CH3CO(CH2)2CO2H}-&#954;2O](PF6) (6).

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Ruthenium phosphine complexes are widely used for homogeneous catalytic reactions such as hydrogenations. The synthesis of a series of novel tridentate ruthenium complexes bearing the N-triphos ligand N(CH2PPh2)3 is reported. Additionally, the stoichiometric reaction of a dihydride Ru&#8211;N-triphos complex with levulinic acid is described.

Herein we report the synthesis of a tridentate phosphine ligand N(CH2PPh2)3 (N-triphosPh) (1) via a phosphorus based Mannich reaction of the ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

Synthesis and Evaluation of a Ruthenium-based Mitochondrial Calcium Uptake Inhibitor

We detail the synthesis and purification of a mitochondrial calcium uptake inhibitor, [(OH2)(NH3)4Ru(&#181;-O)Ru(NH3)4(OH2)]5+. The optimized synthesis of this compound commences from [Ru(NH3)5Cl]Cl2 in 1 M NH4OH in a closed container, yielding a green solution. Purification is accomplished with cation-exchange chromatography. This compound is characterized and verified to be pure by UV-vis and IR spectroscopy. The mitochondrial calcium uptake inhibitory properties are assessed in permeabilized HeLa cells by fluorescence spectroscopy.

A protocol for the synthesis, purification, and characterization of a ruthenium-based inhibitor of mitochondrial calcium uptake is presented. A procedure to evaluate its efficacy in permeabilized mammalian cells is demonstrated.

We detail the synthesis and purification of a mitochondrial calcium uptake inhibitor, [(OH2)(NH3)4Ru(&#181;-O)Ru(NH3)4(OH2)]5+. The optimized synthesis of ...

Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

We report a method to generate the N-heterocyclic carbene (NHC) 1,3-dimesitylimidazol-2-ylidene (IMes) under UV-irradiation at 365 nm to characterize IMes and determine the corresponding photochemical mechanism. Then, we describe a protocol to perform ring-opening metathesis polymerization (ROMP) in solution and in miniemulsion using this NHC-photogenerating system. To photogenerate IMes, a system comprising 2-isopropylthioxanthone (ITX) as the sensitizer and 1,3-dimesitylimidazolium tetraphenylborate (IMesH+BPh4-) as the protected form of NHC is employed. IMesH+BPh4- can be obtained in a single step by anion exchange between 1,3-dimesitylimidazolium chloride and sodium tetraphenylborate. A real-time steady-state photolysis setup is described, which hints that the photochemical reaction proceeds in two consecutive steps: 1) ITX triplet is photo-reduced by the borate anion and 2) subsequent proton transfer takes place from the imidazolium cation to produce the expected NHC IMes. Two separate characterization protocols are implemented. Firstly, CS2 is added to the reaction media to evidence the photogeneration of NHC through formation of the IMes-CS2 adduct. Secondly, the amount of NHC released in situ is quantified using acid-base titration. The use of this NHC photo-generating system for the ROMP of norbornene is also discussed. In solution, a photopolymerization experiment is conducted by mixing ITX, IMesH+BPh4-, [RuCl2(p-cymene)]2 and norbornene in CH2Cl2, then irradiating the solution in a UV reactor. In a dispersed medium, a monomer miniemulsion is first formed then irradiated inside an annular reactor to produce a stable poly(norbornene) latex.

We describe a protocol to photogenerate N-heterocyclic carbenes (NHCs) by UV irradiation of a 2-isopropylthioxanthone/imidazolium tetraphenylborate salt system. Methods to characterize the photoreleased NHC and elucidate the photochemical mechanism are proposed. The protocols for ring-opening metathesis photopolymerization in solution and miniemulsion illustrate the potential of this 2-component NHC photogenerating system.

We report a method to generate the N-heterocyclic carbene (NHC) 1,3-dimesitylimidazol-2-ylidene (IMes) under UV-irradiation at 365 nm to characterize IMes ...

Multiscale Sampling of a Heterogeneous Water/Metal Catalyst Interface using Density Functional Theory and Force-Field Molecular Dynamics

A significant number of heterogeneously-catalyzed chemical processes occur under liquid conditions, but simulating catalyst function under such conditions is challenging when it is necessary to include the solvent molecules. The bond breaking and forming processes modeled in these systems necessitate the use of quantum chemical methods. Since molecules in the liquid phase are under constant thermal motion, simulations must also include configurational sampling. This means that multiple configurations of liquid molecules must be simulated for each catalytic species of interest. The goal of the protocol presented here is to generate and sample trajectories of configurations of liquid water molecules around catalytic species on flat transition metal surfaces in a way that balances chemical accuracy with computational expense. Specifically, force field molecular dynamics (FFMD) simulations are used to generate configurations of liquid molecules that can subsequently be used in quantum mechanics-based methods such as density functional theory or ab initio molecular dynamics. To illustrate this, in this manuscript, the protocol is used for catalytic intermediates that could be involved in the pathway for the decomposition of glycerol (C3H8O3). The structures that are generated using FFMD are modeled in DFT in order to estimate the enthalpies of solvation of the catalytic species and to identify how H2O molecules participate in catalytic decompositions.

The goal of the protocol presented here is to generate and sample trajectories of configurations of liquid water molecules around catalytic species on a flat transition metal surface. The sampled configurations can be used as starting structures in quantum mechanics-based methods.

A significant number of heterogeneously-catalyzed chemical processes occur under liquid conditions, but simulating catalyst function under such conditions ...

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared according to the methodology developed by surface organometallic chemistry (SOMC). In this framework, catalytic cycles can be determined by isolating crucial intermediates. All air-sensitive materials are handled under inert atmosphere (using gloveboxes or a Schlenk line) or high vacuum lines (HVLs, &#60;10-5 mbar). The preparation of SiO2-700 (silica dehydroxylated at 700 &#176;C) and subsequent applications (the grafting of complexes and catalytic runs) requires the use of HVLs and double-Schlenk techniques. Several well-known characterization methods are used, such as Fourier-transform infrared spectroscopy (FTIR), elemental microanalysis, solid-state nuclear magnetic resonance spectroscopy (SSNMR), and state-of-the-art dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP-SENS). FTIR and elemental microanalysis permit scientists to establish the grafting and its stoichiometry. 1H and 13C SSNMR allows the structural determination of the hydrocarbon ligands coordination sphere. DNP SENS is an emerging powerful technique in solid characterization for the detection of poorly sensitive nuclei (15N, in our case). SiO2-700 is treated with about one equivalent of the metal precursor compared to the amount of surface silanol (0.30 mmol&#183;g-1) in pentane at room temperature. Then, volatiles are removed, and the powder samples are dried under dynamic high vacuum to afford the desired materials [(&#8801;Si-O-)Hf(&#951;2&#960;-MeNCH2)(&#951;1-NMe2)(&#951;1-HNMe2)]. After a thermal treatment under high vacuum, the grafted complex is converted into metal imido silica complex [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)]. [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] effectively promotes the metathesis of imines, using the combination of two imine substrates, N-(4-phenylbenzylidene)benzylamine, or N-(4-fluorobenzylidene)-4-fluoroaniline, with N-benzylidenetert-butylamine as substrates. A significantly lower conversion is observed with the blank runs; thus, the presence of the imido group in [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is correlated to the catalytic performance.

A new group IV metal catalyst for imine metathesis is prepared by grafting amine metal complex onto dehydroxylated silica. Surface metal fragments are characterized using FT-IR, elemental microanalysis, and solid-state NMR spectroscopy. Further dynamic nuclear polarization surface enhanced NMR spectroscopy experiments complement the determination of the coordination sphere.

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared ...

Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid nanosheets, a series of Pt/xHMNO6/CNTs with different solid acid compositions (x = 5, 20 wt%; M = Nb, Ta; N = Mo, W) have been prepared by carbon nanotube pretreatment, protonic exchange, solid acid exfoliation, aggregation and finally Pt particles impregnation. The Pt/xHMNO6/CNTs are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and NH3-temperature programmed desorption. The study revealed that HNbWO6 nanosheets were attached on CNTs, with some edges of the nanosheets being bent in shape. The acid strength of the supported Pt catalysts increases in the following order: Pt/CNTs &#60; Pt/5HNbWO6/CNTs &#60; Pt/20HNbMoO6/CNTs &#60; Pt/20HNbWO6/CNTs &#60; Pt/20HTaWO6/CNTs. In addition, the catalytic hydroconversion of lignin-derived model compound: diphenyl ether using the synthesized Pt/20HNbWO6 catalyst has been investigated.

A protocol for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs is presented.

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid ...

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of the reaction site in metal-organic framework (MOF)&#8211;based catalysts in an enantioselective catalytic reaction system. Therefore, a method of validating the reaction site of MOF-based catalysts is necessary to investigate this issue. Substrate size discrimination by pore size was accomplished by comparing the substrate size versus the reaction rate in two different types of carbonyl-ene reactions with two kinds of MOFs. The MOF catalysts were used to compare the performance of the two reaction types (Zn-mediated stoichiometric and Ti-catalyzed carbonyl-ene reactions) in two different media. Using the proposed method, it was observed that the entire MOF crystal participated in the reaction, and the interior of the crystal pore played an important role in exerting chiral control when the reaction was stoichiometric. Homogeneity of the chiral environment of MOF catalysts was established by the size control method for a particle used in the Zn-mediated stoichiometric reaction system. The protocol proposed for the catalytic reaction revealed that the reaction mainly occurred on the catalyst surface regardless of the substrate size, which reveals the actual reaction sites in MOF-based heterogeneous catalysts. This method for reaction site validation of MOF catalysts suggests various considerations for developing heterogeneous enantioselective MOF catalysts.

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs

Here, we present a protocol for active site validation of metal-organic framework catalysts by comparing stoichiometric and catalytic carbonyl-ene reactions to find out whether a reaction takes place on the inner or outer surface of metal-organic frameworks.

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of ...

Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands like amines are removed by diverse pre-treatment procedures before use in heterogeneous catalysis as amines are considered as a catalyst poison. However, a possible beneficial influence of these surface modifiers on hydrogenation reactions, which is known from spectator species on metal surfaces, is often neglected.
Therefore, amine-stabilized Pt nanoparticles supported by titania (P25) were used without any pre-treatment in order to elucidate a possible influence of the ligand in liquid phase hydrogenation reactions. The catalytic activity of amine-stabilized Pt nanoparticles of two different sizes was investigated in a double-walled stirring tank reactor at 69 &#176;C to 130 &#176;C and 1 atm hydrogen pressure. The conversion of cyclohexene to cyclohexane was determined by gas chromatography (GC) and was compared to ligand-free Pt particles. All catalysts were checked before and after reaction by transmission electron spectroscopy (TEM) and X-ray photoelectron spectroscopy (XPS) for possible changes in size, shape, and ligand shell. The hydrogenation of cyclohexene in liquid phase revealed a higher conversion for amine-stabilized Pt nanoparticles on titania than the ligand-free particles. The hydrogenation of 5-methylfurfural (5-MF) was chosen for a further test reaction, since the hydrogenation of &#945;, &#946;-unsaturated aldehydes is more complex and exhibits various reaction paths. However, XPS and infrared spectroscopy (IR) proved that 5-MF acts as catalyst poison at the given reaction conditions.

This protocol shows a convenient method for comparing the catalytic properties of supported platinum catalysts, synthesized by deposition of nanosized colloids or by impregnation. The hydrogenation of cyclohexene serves as a model reaction to determine the catalytic activity of the catalysts.

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands ...

Heterogeneous Removal of Water-Soluble Ruthenium Olefin Metathesis Catalyst from Aqueous Media Via Host-Guest Interaction

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