Name: development of heterogeneous enantioselective catalysts using chiral metal-organic frameworks (mofs)
Uploaded: 2020-01-17T15:00:00
Description: Watch this Scientific Journal Video about Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs at JoVE.com

This work was supported by a National Research Foundation of Korea (NRF) Basic Science Research Program NRF-2019R1A2C4070584 and the Science Research Center NRF-2016R1A5A1009405 funded by the Korea government (MSIP). S. Kim was supported by NRF Global Ph.D. Fellowship (NRF-2018H1A2A1062013).

1. Preparation of (S)-KUMOF-1 crystals in three sizes
NOTE: Each step follows the experimental section and supplementary information of previous reports2,24,27. Three different sizes of (S)-KUMOF-1 were prepared: large (S)-KUMOF-1-(L), medium (S)-KUMOF-1-(M), and small (S)-KUMOF-1-(S) with pa...

<ol>
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After the synthesis of (S)-KUMOF-1, crystals in some vials seem to be powdery and are not appropriate for use in catalysis. Therefore, proper crystals of (S)-KUMOF-1 need to be selected. The yield of (S)-KUMOF-1 is calculated using only those vials in which it was successfully synthesized. When withdrawn from the solvent, (S)-KUMOF-1 dismantles. Therefore, the crystals should always be kept wet. For this reason, weighi...

MOFs are considered a useful heterogeneous catalyst for chemical reactions. There are many different reported uses of MOFs for enantioselective catalysis1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19. Still, it has yet to be determined whether the reactions take place on the inner or outer surface of the MOFs. Recent studies have raised questions concerning the utilization of the available surface and reduced diffusion20,21,22,23. A more striking issue is that the chiral environment varies with the location of each cavity in the MOF crystal. This heterogeneity of the chiral environment implies that the stereoselectivity of the reaction product depends on the reaction site24. Thus, designing an efficient enantioselective catalyst requires identification of the location where the reaction would take place. To do so, it is necessary to ensure that the reaction occurs either only on the inner surface or only on the outer surface of the MOF while leaving the interior intact. The porous structure of MOFs and their large surface area containing chiral environment active sites can be exploited for enantioselective catalysis. For this reason, MOFs are excellent replacements of solid-supported heterogeneous catalysts25. The use of MOFs as heterogeneous catalysts needs to be reconsidered if the reaction does not occur inside them. The location of the reaction site is important, as well as the size of the cavity. In porous materials, the size of the cavity determines the substrate based on its size. There are some reports of MOF-based catalysts that overlook the cavity size issue25. Many MOF-based catalysts introduce bulky catalytic species (e.g., Ti(O-iPr)4) to the original framework structure3,8,13. There is a change in the cavity size when bulky catalytic species are adopted in the original framework structure. The reduced cavity size caused by the bulky catalytic species makes it impossible for the substrate to fully diffuse into the MOFs. Thus, discrimination of substrate size by the cavity size of the MOFs needs to be considered for these cases. The catalytic reactions by MOFs often make it difficult to support evidence of reactions taking place inside the MOF cavity. Some studies have shown that substrates larger than the MOF cavities are converted to the expected products with ease, which seems contradictory8,13. These results can be interpreted as a contact between the functional group of the substrate and catalytic site initiating the catalytic reaction. In this case, there is no need for the substrate to diffuse into the MOFs; the reaction occurs on the surface of the MOF crystals26 and the cavity size is not directly involved in the discrimination of the substrate based on its size.
To identify the reaction sites of MOFs, a known Lewis-acid promoted carbonyl-ene reaction was selected2. Using 3-methylgeranial and its congeners as substrates, four types of enantioselective carbonyl-ene reactions (Figure 1) were studied27. The reactions, which have been previously reported, were classified into two classes: a stoichiometric reaction using a Zn reagent and catalytic reactions using a Ti reagent27. The reaction of the smallest substrate requires a stoichiometric amount of Zn/KUMOF-1 (KUMOF = Korea University Metal-Organic Framework); it has been reported that this reaction takes place inside of the crystal27. Two kinds of MOFs were used in this method, Zn/KUMOF-1 for the stoichiometric reaction and Ti/KUMOF-1 for the catalytic reaction. Owing to the distinct reaction mechanisms of these two kinds of MOFs, a comparison between the reaction rate versus substrate size is possible2,28,29. The effect of particle size on the carbonyl-ene reaction with Zn/KUMOF-127 demonstrated that, as seen in the previous report, the chiral environment of the outer surface was different from the inner side of the MOF crystal24. This article demonstrates a method that determines the reaction sites by comparing the reactions of three kinds of substrates with two classes of catalysts and the effect of particle size as reported in the previous paper27.

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			<td>Acetone</td>
			<td>Daejung</td>
			<td>1009-4110</td>
			<td></td>
		</tr>
		<tr>
			<td>Analytical Balance</td>
			<td>Sartorius</td>
			<td>CP224S</td>
			<td></td>
		</tr>
		<tr>
			<td>Copper(II) nitrate trihydrate</td>
			<td>Sigma Aldrich</td>
			<td>61194</td>
			<td></td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>Daejung</td>
			<td>3030-4465</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl zinc</td>
			<td>Acros</td>
			<td>377241000</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl acetate</td>
			<td>Daejung</td>
			<td>4016-4410</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter paper</td>
			<td>Whatman</td>
			<td>WF1-0900</td>
			<td></td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Daejung</td>
			<td>5558-4410</td>
			<td></td>
		</tr>
		<tr>
			<td>Microwave synthesizer</td>
			<td>CEM</td>
			<td></td>
			<td>Discover SP</td>
		</tr>
		<tr>
			<td>Microwave synthesizer 10 mL Vessel Accessory Kit</td>
			<td>CEM</td>
			<td>909050</td>
			<td></td>
		</tr>
		<tr>
			<td>N,N-Diethylformamide</td>
			<td>TCI</td>
			<td>D0506</td>
			<td></td>
		</tr>
		<tr>
			<td>N,N-Dimethylaniline</td>
			<td>TCI</td>
			<td>D0665</td>
			<td></td>
		</tr>
		<tr>
			<td>n-Hexane</td>
			<td>Daejung</td>
			<td>4081-4410</td>
			<td></td>
		</tr>
		<tr>
			<td>Normject All plastic syringe 5 mL luer tip 100/pk</td>
			<td>Normject</td>
			<td>A5</td>
			<td></td>
		</tr>
		<tr>
			<td>Pasteur Pipette 150 mm</td>
			<td>Hilgenberg</td>
			<td>HG.3150101</td>
			<td></td>
		</tr>
		<tr>
			<td>PTFE tape</td>
			<td>KDY</td>
			<td>TP-75</td>
			<td></td>
		</tr>
		<tr>
			<td>Rotary Evaporator</td>
			<td>Eyela</td>
			<td>243239</td>
			<td></td>
		</tr>
		<tr>
			<td>Shaker</td>
			<td>DAIHAN Scientific</td>
			<td>DH.WSO04010</td>
			<td></td>
		</tr>
		<tr>
			<td>Silica gel 60 (230-400 mesh)</td>
			<td>Merck</td>
			<td>109385</td>
			<td></td>
		</tr>
		<tr>
			<td>Synthetic Oven</td>
			<td>Eyela</td>
			<td>NDO-600ND</td>
			<td></td>
		</tr>
		<tr>
			<td>Titanium isopropoxide</td>
			<td>Sigma Aldrich</td>
			<td>87560</td>
			<td></td>
		</tr>
		<tr>
			<td>Vial (20 mL)</td>
			<td>SamooKurex</td>
			<td>SCV2660</td>
			<td></td>
		</tr>
		<tr>
			<td>Vial (5 mL)</td>
			<td>SamooKurex</td>
			<td>SCV1545</td>
			<td></td>
		</tr>
	</tbody>
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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.

The enantioselective carbonyl-ene reaction using the Zn reagent is stoichiometric because of the difference in the binding affinities of the alkoxy and carbonyl groups to the metal (Figure 2). For this reason, the substrates were converted into the products at the reaction site and remained there. The desired products were obtained by dismantling the crystals, as detailed in section 4 of the protocol. The results of the heterogeneous enantioselective carbonyl-ene reaction of substrates by Zn...

Watch this Scientific Journal Video about Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs at JoVE.com

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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.

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 ...

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Synthesis of a Water-soluble MetalÃ¢â‚¬â€œOrganic Complex Array (Video) | JoVE

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

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance (Video) | JoVE

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes

Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes (Video) | JoVE

We report the synthesis of thin, highly intergrown, polycrystalline metal-organic framework (MOF) membranes on a wide range of unmodified porous and ...

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks (Video) | JoVE

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. ...

A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks

A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks (Video) | JoVE

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural ...

Synthesis of Low-Valent MOFs from Multitopic Phosphine Linkers

Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers

Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers (Video) | JoVE 

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, ...

Magnetometric Characterization of Redox-Active MOFs Solid-State Electrochemistry

Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks

Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks (Video) | JoVE 

Electrochemical energy storage has been a widely discussed application of redox-active metal-organic frameworks (MOFs) in the past 5 years. Although MOFs ...

Triazole and Tetrazole Functionalized Zr-MOFs Synthesis and Characterization

Synthesis of Triazole and Tetrazole-Functionalized Zr-Based Metal-Organic Frameworks Through Post-Synthetic Ligand Exchange

Functionalizing Metal-Organic Frameworks: Advancements, Challenges, and the Power of Post-Synthetic Ligand Exchange (Video) | JoVE

Metal-organic frameworks (MOFs) are a class of porous materials that are formed through coordination bonds between metal clusters and organic ligands. ...