Name: heterogeneous removal of water-soluble ruthenium olefin metathesis catalyst from aqueous media via host-guest interaction
Uploaded: 2018-08-23T14:00:00
Description: Watch this Scientific Journal Video about Heterogeneous Removal of Water-Soluble Ruthenium Olefin Metathesis Catalyst from Aqueous Media Via Host-Guest Interaction at JoVE.com

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. Sy...

<ol>
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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 border="0" cellpadding="0" cellspacing="0" style="width:767px;" width="767">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Hoveyda-Grubbs Catalyst 1st Generation</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:157px;">577944</td>
			<td style="width:167px;">Air sensitivie. Light sensitivie.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Diethyl diallylmalonate</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:157px;">283479</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Ethyl vinyl ether</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:157px;">422177</td>
			<td>Air sensitive.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Aluminum oxide</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:157px;">06300</td>
			<td>Activated, neutral, Brockmann Activity I</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:283px;">Potassium bis(trimethylsilyl)amide solution (0.5 M in toluene)</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:157px;">277304</td>
			<td>Moisture sensitive.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Etyhl acetate</td>
			<td style="width:160px;">VWR</td>
			<td style="width:157px;">BDH1123</td>
			<td>Flammable liquid.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Methanol</td>
			<td style="width:160px;">VWR</td>
			<td style="width:157px;">BDH1135</td>
			<td>Flammable liquid. Toxic.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Deuterium Oxide 99.8%D</td>
			<td style="width:160px;">TCI</td>
			<td style="width:157px;">W0002</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:283px;">Methylene Chloride-D2 (D, 99.8%)</td>
			<td style="width:160px;">Cambridge Isotope Laboratories, Inc.</td>
			<td style="width:157px;">DLM-23</td>
			<td>Flammable liquid. Toxic.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Activated carbon</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:157px;">242276</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Magnesium sulfate</td>
			<td style="width:160px;">EMD Millipore</td>
			<td style="width:157px;">MX0075</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Ethyl ether</td>
			<td style="width:160px;">EMD Millipore</td>
			<td style="width:157px;">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...

Watch this Scientific Journal Video about Heterogeneous Removal of Water-Soluble Ruthenium Olefin Metathesis Catalyst from Aqueous Media Via Host-Guest Interaction at JoVE.com

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 ...

This method can help answer key questions in the practical application of transition metal catalyst field, such as polymer science and pharmaceutical industries. We can produce ultra pure product using this technology. The main advantage of this technique is that we can easily remove the homogeneous catalyst which is difficult to do by using Host-Guest Interaction.The implications of this technique extend toward recyclable homogeneous catalysis, because the catalyst removal method, Host-Guest Interaction is reversible. Though this method can provide insight into the same metastasis catalyst removal. It can also be applied to other metal containing catalyst such as palladium, platinum, copper, nickel and gold catalyst.Visual demonstration of this method is critical as the synthesis procedure and homogeneous catalyst removal are typical too long because Host-Guest Catalyst remover is new. First dry a 25 milliliter round bottom flask containing a magnetic stir bar, a 20 milliliter vial and a spatula in an oven. Place 118 milligrams of imidazolium salt in a 4 milliliter vial.Place the prepared imidazolium salt, the dried glassware, a septum, and the spatula in a glovebox chamber and vacuum for 2 hours. After completely removing the air in the glovebox can chamber, purge inert gas into the chamber. Then move the imidazolium salt, glassware, septum and spatula into the glovebox.In the glovebox, add 54 milligrams of first generation Hoveyda-Grubbs catalyst in the 20 milliliter vial. Dissolve the imidazolium salt in two milliliters of toluene, and transfer it into the 25 milliliter round bottom flask containing the magnetic stir bar. Next, add 0.18 milliliters of a 0.5 molar KH MDS solution to the imidazolium salt solution.Swirl the flask to mix the reagents. Now dissolve the catalyst in three milliliters of toluene and add the solution to the reaction flask. Seal the flask with the septum.Then remove the flask from the glovebox. Following this, stir the reaction mixture for three hours at 80 degrees Celsius. After cooling the reaction mixture to room temperature, purify the catalyst by chromatography on neutral alumina.Using a 15 to one mixture of ethyl acetate and methanol, collect the dark green solution. After combining the fractions containing product, removed the solvent under reduced pressure. When finished, dry the final residue under vacuum to obtain a dark green waxy solid.Prepare degassed deuterium oxide by bubbling with nitrogen gas for over two hours. Add 4.4 milligrams of the ruthenium catalysts and 41 milligrams of the tetra alkyl ammonium substrate in separate four milliliter vials. Dissolve the tetra alkyl ammonium substrate in 0.5 milliliters of degassed deuterium dioxide.Then add the solution to the catalyst. Seal the reaction vial and heat the reaction mixture for 24 hours at 45 degrees Celsius. Monitor the reaction conversion by proton NMR.After the reaction is complete, cool the reaction vial to room temperature. Then add 150 milligrams of beta CD grafted silica to the reaction mixture. Stir the reaction mixture for 10 hours at room temperature.After 10 hours, filter the reaction mixture through a cotton plug. Then remove the solvent in a freeze dryer. Prepare degassed deuterium oxide by bubbling with nitrogen gas for over two hours.At 4.4 milligrams of the ruthenium catalysts and 17.1 milligrams of monomer in separate four milliliter vials. Dissolve the monomer in 0.5 milliliters of degassed deuterium oxide. Then add the solution to the catalyst.Seal the reaction vial and heat the reaction mixture for two hours at 45 degrees Celsius. Monitor the reaction conversion by proton NMR. After the reaction is complete, cool the reaction vial to room temperature.Then quench the reaction mixture with 0.1 milliliters of ethyl vinyl ether. Next, add 150 milligrams of beta CD grafted silica to the reaction mixture. Stir the reaction mixture for 10 hours at room temperature.Filter the reaction mixture through a cotton plug. Then remove the solvent in a freeze dryer. Add 4.4 milligrams of the ruthenium catalysts and 48 milligrams of diethyl diallylmalonate in separate form in little vials.Dissolve the diethyl diallylmalonate in 0.5 milliliters of dichloromethane. Then add the solution to the catalyst. Seal the reaction vial and keep the reaction mixture at room temperature for one hour.Monitor the reaction conversion by proton NMR. After the reaction is complete, transfer the reaction mixture to a 30 milliliter vial. Dilute the mixture with 15 milliliters of diethyl ether.Then wash the organic solution five times with 15 milliliters of water. Dry the organic layer with magnesium sulfate. Then filter the solution through a cotton plug to remove the magnesium sulfate.Following this, add a magnetic stir bar and 60 milligrams of activated carbon to the filtered solution. Stir the mixture for 24 hours at room temperature. Filter the solution through a cotton plug to remove the activated carbon.Finally, remove the solvent under reduced pressure. The ligand exchange reaction for the ruthenium olefin metathesis catalysis is shown here. The proton NMR spectrum is displayed here.The ring closing metathesis reaction, an aqueous solution, and subsequent removal of used catalyst via Host-Guest Interaction is shown here. The dark reaction solution turned clear after the Host-Guest removal. The quaternary ammonium substrate was fully converted into the corresponding product with one mole percent of the catalyst and 53 parts per million of residual ruthenium was detected in the final product by inductively coupled plasma mass spectrometry or ICP-MS.Full conversion of the primary ammonium substrate was achieved with three mole percent of the catalyst, and the residual ruthenium level in the product was 284 parts per million. Ring-opening metathesis polymerisation and aqueous solution is displayed here. And the residual ruthenium content detected by ICP-MS was 269 parts per million.The ring closing metathesis reaction in dichloromethane and subsequent removal of used catalyst via extraction is shown here. With the exception of highly hindered substrates, the substrates achieved complete conversion in the ring closing metathesis reaction with one mole percent of the catalyst. ICP-MS detected 5.9 parts per million of ruthenium in the product.Without activated carbon treatment, the residual ruthenium level was 63 parts per million which is not acceptable for pharmaceutical purposes. This technique can be done in 12 hours if it is performed properly. My research group is currently doing research to shorten the time, and to increase the efficiency of catalyst removal.While attempting this procedure, it is important to remember to add sufficient guest bound solid to capture all available hosts containing catalyst molecules. Following this procedure, other catalysts like a palladium, platinum, copper, nickel and gold centered catalyst can be easily removed from the product by using the new guest containing NHC ligand and Host-Guest Interaction principle. After its development, this technique paved the way for researchers in the field of organometallic catalysis to explore the convenient and efficient removal methods of homogeneous catalysts to produce ultra pure polymers and pharmaceutical products.After watching this video, you should have a good understanding of how to remove a homogeneous organometallic catalysts from a reaction mixture by Host-Guest Interaction. Don't forget that working with ethyl acetate methanol, ethylene chloride and diethyl ether can be extremely hazardous. Precautions such as conducting the reaction in the fume hood should always be taken while performing this procedure.

heterogeneous-removal-water-soluble-ruthenium-olefin-metathesis

Research

JoVE Journal

Chemistry

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

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 ...

Water in Oil Emulsions: A New System for Assembling Water-soluble Chlorophyll-binding Proteins with Hydrophobic Pigments

Chlorophylls (Chls) and bacteriochlorophylls (BChls) are the primary cofactors that carry out photosynthetic light harvesting and electron transport. Their functionality critically depends on their specific organization within large and elaborate multisubunit transmembrane protein complexes. In order to understand at the molecular level how these complexes facilitate solar energy conversion, it is essential to understand protein-pigment, and pigment-pigment interactions, and their effect on excited dynamics. One way of gaining such understanding is by constructing and studying complexes of Chls with simple water-soluble recombinant proteins. However, incorporating the lipophilic Chls and BChls into water-soluble proteins is difficult. Moreover, there is no general method, which could be used for assembly of water-soluble proteins with hydrophobic pigments. Here, we demonstrate a simple and high throughput system based on water-in-oil emulsions, which enables assembly of water-soluble proteins with hydrophobic Chls. The new method was validated by assembling recombinant versions of the water-soluble chlorophyll binding protein of Brassicaceae plants (WSCP) with Chl a. We demonstrate the successful assembly of Chl a using crude lysates of WSCP expressing E. coli cell, which may be used for developing a genetic screen system for novel water-soluble Chl-binding proteins, and for studies of Chl-protein interactions and assembly processes.

This manuscript describes a simple and high-throughput method for assembling water-soluble proteins with hydrophobic pigments that is based on water-in-oil emulsions. We demonstrate the effectiveness of the method in the assembly of native chlorophylls with four variants of recombinant water-soluble-chlorophyll binding proteins (WSCPs) of Brassica plants expressed in E. coli.

Chlorophylls (Chls) and bacteriochlorophylls (BChls) are the primary cofactors that carry out photosynthetic light harvesting and electron transport. ...

HKUST-1 as a Heterogeneous Catalyst for the Synthesis of Vanillin

Vanillin (4-hydoxy-3-methoxybenzaldehyde) is the main component of the extract of vanilla bean. The natural vanilla scent is a mixture of approximately 200 different odorant compounds in addition to vanillin. The natural extraction of vanillin (from the orchid Vanilla planifolia, Vanilla tahitiensis and Vanilla pompon) represents only 1% of the worldwide production and since this process is expensive and very long, the rest of the production of vanillin is synthesized. Many biotechnological approaches can be used for the synthesis of vanillin from lignin, phenolic stilbenes, isoeugenol, eugenol, guaicol, etc., with the disadvantage of harming the environment since these processes use strong oxidizing agents and toxic solvents. Thus, eco-friendly alternatives on the production of vanillin are very desirable and thus, under current investigation. Porous coordination polymers (PCPs) are a new class of highly crystalline materials that recently have been used for catalysis. HKUST-1 (Cu3(BTC)2(H2O)3, BTC = 1,3,5-benzene-tricarboxylate) is a very well known PCP which has been extensively studied as a heterogeneous catalyst. Here, we report a synthetic strategy for the production of vanillin by the oxidation of trans-ferulic acid using HKUST-1 as a catalyst.

The conversion of trans-ferulic acid to vanillin was achieved by heterogeneous catalysis. HKUST-1 was employed in this synthesis and the essential step in the catalytic process was the generation of unsaturated metal sites. Thus, when the catalyst was activated under vacuum, full vanillin conversion (yield of 95%) was obtained.

Vanillin (4-hydoxy-3-methoxybenzaldehyde) is the main component of the extract of vanilla bean. The natural vanilla scent is a mixture of approximately ...

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.

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

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 ...

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity in aqueous CO2 reduction. Different from traditional metal nanocrystals, the synthesis of metal single atoms involves a matrix material that can confine those single atoms and prevent them from aggregation. We report an electrospinning and thermal annealing method to prepare Ni single atoms dispersed and coordinated in a graphene shell, as active centers for CO2 reduction to CO. During the synthesis, N dopants play a critical role in generating graphene vacancies to trap Ni atoms. Aberration-corrected scanning transmission electron microscopy and three-dimensional atom probe tomography were employed to identify the single Ni atomic sites in graphene vacancies. Detailed setup of electrochemical CO2 reduction apparatus coupled with an on-line gas chromatography is also demonstrated. Compared to metallic Ni, Ni single atom catalyst exhibit dramatically improved CO2 reduction and suppressed H2 evolution side reaction.

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Here, we present a protocol for the synthesis and electrochemical testing of transition metal single atoms coordinated in graphene vacancies as active centers for selective carbon dioxide reduction to carbon monoxide in aqueous solutions.

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

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 ...