Name: synthesis of a thiol building block for the crystallization of a semiconducting gyroidal metal-sulfur framework
Uploaded: 2018-04-09T13:00:00
Description: Watch this Scientific Journal Video about Synthesis of a Thiol Building Block for the Crystallization of a Semiconducting Gyroidal Metal-sulfur Framework at JoVE.com

This work was supported by the National Natural Science Foundation of China (21471037), Guangdong Natural Science Funds for Distinguished Young Scholars (15ZK0307), Science and Technology Planning Project of Guangdong Province (2017A050506051), and the Research Grants Council of HKSAR [GRF 11303414].

Caution: Please consult all relevant material safety data sheets before use. Methyl disulfide and sodium thiomethoxide are strongly malodorous and should be handled in a fume hood. Sodium metal is highly reactive and requires special safety precautions against potential fire and explosion hazards. In addition to the use of a fume hood, personal protective equipment (safety glasses, gloves, lab coat, full length pants, and closed-toe shoes) should be properly employed. Portions of the following procedures involve standard...

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The reaction between the bromo group and the thiomethoxide anion apparently first produced the methyl thioether, which was then demethylated by the excess thiomethoxide to provide the thiolate anion product. To ensure complete conversion to the desired thiolate anion (especially for a polybromide substrate like HBT), the vigorous conditions of prolonged heating (e.g., 240 &#176;C over 48 h) with a large excess of sodium thiomethoxide (e.g., over three times the moles of the bromo groups) are essential. ...

There is currently great interest in employing strong, polarizable metal-sulfur (e.g., metal-thiolate) links for constructing open framework materials with enhanced electrocatalytic and conductive properties1,2,3,4,5,6,7,8,9,10. In addition to promoting electronic interaction and transport in the extended state, the soft and covalent metal-sulfur links also impart better stability for applications in aqueous environments. Among the sulfur-equipped building blocks, symmetrical, multidentate polycyclic aromatic building blocks like 2,3,6,7,10,11-triphenylene hexathiol (HTT)9,11,12,13,14 not only supply highly polarizable &#960;-electrons, but also offer distinct advantages with respect to framework design and synthesis. First, the rigid and symmetrical triphenylene core, in conjunction with the chelating dithiolene groups of HTT, serves to lock in metal ions in regular bonding motifs, simplifying the structural prediction of the prospective network7,15. Together with the rigid and open geometry of the sulfur linker, framework structures with substantial porosity features can often be achieved in the solid state.
One major challenge in assembling thiol-equipped metal orangic framework (MOF) materials is rooted in the synthesis of the organic linker molecules. In a classical protocol, the thiol group had to be derived from the phenol group using the Newman-Kwart rearrangement of the O-aryl thiocarbamate precursor16,17,18. This approach, however, involves elaborate preparative steps for the phenol precursor molecule as well as potential complications of a high-temperature solid phase transformation. Another way of making thiols utilizes reductive dealkylation of thioethers under the harsh conditions of, for example, sodium metal in liquid ammonia19,20,21,22, and is not compatible with the carboxyl and many other donor functions for network construction.
By comparison, the protocol presented here has multiple advantages: safety, convenience, cost-effectiveness, and compatibility with other functional groups (e.g., carbonitrile and pyridinyl). By vigorously heating the generally inexpensive aromatic halide (e.g., hexabromotriphenylene) and thiomethoxide anion, the thiolate anion was generated (via the methyl thioether intermediate product) and then acylated to give the stable and easy-to-handle thioester product-all in one pot.
We will also describe a procedure for utilizing the thioester molecules as the masked form of the thiol linkers for accessing a single-crystalline semiconducting and porous metal-dithiolene network. Unlike the highly reactive free-standing thiols, which tend to decompose and complicate the crystallization of metal-thiolate open frameworks, the thioester can be readily cleaved (e.g., by NaOH or ethylenediamine) in situ to provide the thiol species, serving to mitigate the reaction between the mercaptan units and the metal centers, and to consequently improve the crystallization.
This protocol of preparing thiol/thioester has not been widely used by other groups for the emerging field of metal-sulfur frameworks, even though nucleophilic dealkylations of alkyl aryl thioethers by thiolate anions have already been well documented by organic chemists23,24,25,26. By showcasing this efficient synthetic method for thioesters and their use for facilitating the crystallization of metal-sulfur networks, we wish to promote further efforts to bridge the intellectual and practical divide between synthetic organic chemistry and solid state chemistry, so as to help the speedy and healthy development of porous frameworks.

<table border="0" cellpadding="0" cellspacing="0" width="850">
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Bromine</td>
			<td style="width:348px;">DAMAO CHEMICAL REAGENT FACTORY</td>
			<td style="width:119px;">7726-95-6</td>
			<td style="width:167px;">Highly toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Triphenylene&#160;&#160;</td>
			<td style="width:348px;">HWRK Chem</td>
			<td style="width:119px;">HWG45510</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Iron powder</td>
			<td style="width:348px;">Sigma-Aldrich</td>
			<td style="width:119px;">12310</td>
			<td></td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:216px;">Nitrobenzene</td>
			<td style="width:348px;">DAMAO CHEMICAL REAGENT FACTORY</td>
			<td style="width:119px;">2934</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:216px;">Diethyl ether&#160;</td>
			<td style="width:348px;">DAMAO CHEMICAL REAGENT FACTORY</td>
			<td style="width:119px;">48</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:216px;">Dichloromethane</td>
			<td style="width:348px;">DAMAO CHEMICAL REAGENT FACTORY</td>
			<td>3067</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Sodium metal</td>
			<td style="width:348px;">J&#38;K</td>
			<td style="width:119px;">WM-NMS-54-25X-50G</td>
			<td>Air sensitive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tetrahydrofuran</td>
			<td style="width:348px;">J&#38;K</td>
			<td style="width:119px;">315353</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Dimethyl disulfide</td>
			<td style="width:348px;">INTERNATIONAL LABORATORY USA</td>
			<td style="width:119px;">726415</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1,3-Dimethyl-2-imadazolidinone</td>
			<td style="width:348px;">J&#38;K</td>
			<td style="width:119px;">50483</td>
			<td>Dried over 4&#197; sieves</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Valeryl&#160; chloride</td>
			<td style="width:348px;">J&#38;K</td>
			<td style="width:119px;">99590</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Methanol</td>
			<td style="width:348px;">Guangzhou Chemical Reagent Factory</td>
			<td>2334</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sodium hydroxide</td>
			<td style="width:348px;">Guangzhou Chemical Reagent Factory</td>
			<td style="width:119px;">1588</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ethylene diamine</td>
			<td style="width:348px;">Riedel-de Ha&#235;n</td>
			<td style="width:119px;">15070</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Lead acetate trihydrate</td>
			<td>PEKING CHEMICAL WORKE</td>
			<td style="width:119px;">861218</td>
			<td></td>
		</tr>
	</tbody>
</table>

synthesis of a thiol building block for the crystallization of a semiconducting gyroidal metal-sulfur framework

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and porous metal-dithiolene network in the highly ordered single crystalline state. Unlike the highly reactive free-standing thiols, which tend to decompose and complicate the crystallization of metal-thiolate open frameworks, the thioester reacts in situ to provide the thiol species, serving to mitigate the reaction between the mercaptan units and the metal centers, and to improve crystallization consequently. Specifically, the thioester was synthesized in a one-pot procedure: an aromatic bromide (hexabromotriphenylene) reacted with excess sodium thiomethoxide under vigorous conditions to first form the thioether intermediate product. The thioether was then demethylated by the excess thiomethoxide to provide the thiolate anion that was acylated to form the thioester product. The thioester was conveniently purified by standard column chromatography, and then used directly in the framework synthesis, wherein NaOH and ethylenediamine serve to revert in situ the thioester to the thiol linker for assembling the single-crystalline Pb(II)-dithiolene network. Compared with other methods for thiol synthesis (e.g., by cleaving alkyl thioether using sodium metal and liquid ammonia), the thioester synthesis here uses simple conditions and economical reagents. Moreover, the thioester product is stable and can be conveniently handled and stored. More importantly, in contrast to the generic difficulty in accessing crystalline metal-thiolate open frameworks, we demonstrate that using the thioester for in situ formation of the thiol linker greatly improves the crystallinity of the solid-state product. We intend to encourage broader research efforts on the technologically important metal-sulfur frameworks by disclosing the synthetic protocol for the thioester as well as the crystalline framework solid.

The IR spectrum of the HVaTT molecule (collected by the KBr pellet method) features its strongest absorption at 1,700 cm-1, in accordance with the carbonyl stretching of the thioester functional group. The 1H-NMR spectrum of HVaTT (400 MHz, CDCl3) reveals a singlet at &#948; 8.47 from the aromatic hydrogens, together with 4 multiplets from the aliphatic protons: &#948; 8.47 (s, 6H, CHAr), 2.75 -2.72 (t, J = 7.4, 12H, CH2), 1.81-1.77 (m,...

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Synthesis of a Thiol Building Block for the Crystallization of a Semiconducting Gyroidal Metal-sulfur Framework

Here, we present a one-pot, transition-metal-free synthesis of thiols and thioesters from aromatic halides and sodium thiomethoxide, followed by the preparation of single crystals of a metal-dithiolene network using thiol species generated in situ from the more stable and tractable thioester.

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and ...

The overall goal of this protocol is to synthesize thiol linker molecules and to prepare single crystals of porous, metal-sulfur frameworks from these thiol species. This method can help answer key questions in the field of materials chemistry as to how to better prepare crystalline networks from metal ions and mercaptan molecules. The main advantage of this technique is provided by the convenient and reduced-time synthesis which utilize the relative stable thioester as the precursor for framework assembly.Demonstrating the procedure will be Mr.He Yonghe, a graduate student in my laboratory. To begin the procedure, connect a 200 milliliter Schlenk flask, equipped with a stir bar, to a vacuum-gas manifold. Evacuate and backfill the flask with nitrogen gas three times.From then on, keep the flask filled with flowing nitrogen gas at a slight positive pressure. Next, remove a block of metallic sodium from the mineral oil in which it was stored. Wipe away residual mineral oil with a paper towel and scrape off the oxide layer with a knife.Quickly weigh out approximately 6.7 grams of metallic sodium, and note the weight. Cut the sodium into small pieces and transfer the pieces to the Schlenk flask under a counter-flow of nitrogen gas. Immediately seal the flask with a septum.Add 80 milliliters of anhydrous air-free tetrahydrofuran to the flask via cannula transfer. Then, draw 14.0 milliliters of nitrogen-purged dimethyl disulphide into a syringe. Add the DMDS to the mixture drop wise under a nitrogen atmosphere.Replace the septum with a ground-glass stopper. Then, stir the mixture at room temperature for 24 hours under a flow of nitrogen gas. Then, stir the mixture at 60 degrees celsius for three hours.Ensure that the vacuum manifold is equipped with a cold trap in-line with the gas outlet. With the mixture stirring at 60 degrees celsius, evaporate the THF and excess DMDS under a steady stream of nitrogen gas until a solid has formed. Remove the residual THF and DMDS from the solid under vacuum for two hours to obtain sodium thiomethoxide as a light yellow solid.Store the product under a nitrogen atmosphere in the absence of light. To begin the HVaTT synthesis, connect a 50 milliliter Schlenk flask, equipped with a stir bar, to a vacuum manifold and purge the flask. Quickly measure out approximately 0.664 grams of sodium thiomethoxide and note the weight.Under a counter-flow of nitrogen gas, quickly load the sodium thiomethoxide into the reaction flask, and stopper the flask. Add 0.216 grams of HBT to the flask under a counter-flow of nitrogen gas and seal the flask with a septum. Add 10 milliliters of anhydrous air-free DMEU to the flask via cannula transfer.Afterwards, replace the septum with a ground-glass stopper. Heat the mixture to 240 degrees celsius with a salt bath and stir the mixture under a nitrogen atmosphere for 48 hours. When ready to check the reaction progress, while under a flow of nitrogen gas, use a glass pipette to transfer about 0.1 milliliters of the reaction mixture to a plastic micro-centrifuge vial containing 0.1 milliliters of neat valeroyl chloride.Quickly close the vial. Shake the mixture for one minute. Then, add to the turbid, gray-white mixture 0.4 milliliters of deionized water and 0.1 milliliters of ethyl acetate.Shake the mixture for a few more seconds and allow the mixture to separate. If an insoluble white substance is between the layers, the reaction is likely incomplete. If nothing is observed between the water and ethyl acetate layers, the reaction is potentially complete and the sample may be further examined by thin-layer chromatography.Spot the upper layer on a TLC plate. Develop the plate with a 1 to 4 mixture of ethyl acetate and petroleum ether as the eluent, and visualize the plate with UV light. Examine the plate to determine whether the reaction is complete.Once the reaction is complete, remove the flask from the salt bath and allow the mixture to cool to room temperature. Then cool the mixture to zero degrees celsius with an ice bath. Replace the stopper with a rubber septum.Draw 1.5 milliliters of valeroyl chloride into a syringe. Add the valeroyl chloride to the mixture drop wise over about two minutes while under a nitrogen atmosphere. Replace the septum with a ground-glass stopper and stir the mixture at zero degrees celsius for two hours.Then dilute the mixture with 50 milliliters of ice water. Extract the product into 30 milliliter portions of ethyl acetate three times. Wash the combined organic layers with 60 milliliter portions of deionized water six times.Dry the washed organic fractions over anhydrous magnesium sulfate. Filter off the magnesium sulfate and remove volatiles from the filtrate with a rotary evaporator. Isolate the oily crude product by column chromatography with a 1 to 10 mixture of ethyl acetate and petroleum ether as the eluent.Remove volatiles with a rotary evaporator to obtain a light yellow oil. Combine the oil with five milliliters of methanol, sonicate the mixture for two minutes, and collect the resultant off-white solid product by vacuum filtration. To begin the HTT-Pb synthesis, dissolve 5.7 milligrams of lead two acetate trihydrate in 1.0 milliliters of ethylene diamine in a five milliliter vial.Place 4.6 milligrams of HVaTT, 1.0 milliliters of a degassed 140 millimolar solution of sodium hydroxide in methanol, and 0.7 milliliters of ethylene diamine in a 10 milliliter Schlenk tube. Crystals of various sizes can be obtained by adjusting the solvents and the basicity of the reaction mixture. For example, by varying the ethylene diamine methanol volume ratio between one to two and one to one, and the HVaTT sodium hydroxide molar ratio between one to 14 and one to 28.Sonicate the HVaTT mixture for five minutes. Then add the lead two acetate solution to the HVaTT mixture. Bubble nitrogen gas through the mixture for one minute without stirring.Seal the Schlenk tube with a screw cap and heat the mixture in an oven at 90 degrees celsius for 48 hours. Then allow the mixture to cool to room temperature to grow yellow-orange octahedral single crystals, suitable for single-crystal x-ray diffraction. Use a pipette to remove the solution from the crystals and wash the crystals with methanol several times.Store the washed single crystals in five milliliters of air-free methanol. Next, obtain an aqueous solution of 0.1%by weight paraquot diiodide. Transfer a few HTT-Pb single crystals from the methanol stock to a petri dish.Use laboratory tissue or filter paper to soak up excess methanol in the dish. Carefully apply a few drops of the paraquot diiodide solution to the crystals. Observe the color change of the crystals under a microscope or with the naked eye.The proton NMR spectrum of HVaTT showed a singlet from the aromatic hydrogens and multiplets from the aliphatic protons. Aliphatic C-H stretching was also observed in the HVaTT IR spectrum. The strong absorption at 1700 reciprocal centimeters was attributed to carbonyl stretching from the carbonyls protecting the thioester groups.This carbonyl stretching was correspondingly absent in the IR spectrum of crystalline HTT-Pb. The HTT-Pb also lacked the aliphatic C-H stretching observed in HVaTT. Powder x-ray diffraction of crystalline HTT-Pb was consistent with the reported HTT-Pb single crystal structure.Demonstrating the crystalline-phase purity of the product. The HTT-Pb crystals were highly responsive to paraquot diiodide in water, with the crystals changing color within one to two minutes of contact with an aqueous paraquot diiodide solution. This behavior was attributed to strong charge transfer interactions between the electron-rich HTT-Pb framework and the highly electron-deficient paraquot guest.This technique paves the way for researchers of open framework materials to explore the construction of various metal-thiolate networks for studies of their electronic and catalytic properties. This procedure will facilitate deeper studies on these important metal-sulfur framework materials. Aromatic thioester can also be prepared for molecular chemistry and solution chemistry identification using this procedure.

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