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

Summary

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.

Abstract

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.

Introduction

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 properties^{1,2,3,4,5,6,7,8,9,10}. In addition to promoting electronic interaction and transport in the extended state, the soft and c....

Protocol

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, air-free handling techniques.

1. Preparation of Sodium Thiomethoxide (CH₃SNa)

1. Connect a 200-mL Sc....

Results

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 δ 8.47 from the aromatic hydrogens, together with 4 multiplets from the aliphatic protons: δ 8.47 (s, 6H, CHAr), 2.75 -2.72 (t, J = 7.4, 12H, CH₂), 1.81-1.77 (m, 12H, CH

Discussion

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 °C over 48 h) with a large excess of sodium thiomethoxide (e.g., over three times the moles of the bromo groups) are essential. .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Bromine	DAMAO CHEMICAL REAGENT FACTORY	7726-95-6	Highly toxic
Triphenylene	HWRK Chem	HWG45510
Iron powder	Sigma-Aldrich	12310
Nitrobenzene	DAMAO CHEMICAL REAGENT FACTORY	2934
Diethyl ether	DAMAO CHEMICAL REAGENT FACTORY	48
Dichloromethane	DAMAO CHEMICAL REAGENT FACTORY	3067
Sodium metal	J&K	WM-NMS-54-25X-50G	Air sensitive
Tetrahydrofuran	J&K	315353
Dimethyl disulfide	INTERNATIONAL LABORATORY USA	726415
1,3-Dimethyl-2-imadazolidinone	J&K	50483	Dried over 4Å sieves
Valeryl  chloride	J&K	99590
Methanol	Guangzhou Chemical Reagent Factory	2334
Sodium hydroxide	Guangzhou Chemical Reagent Factory	1588
Ethylene diamine	Riedel-de Haën	15070
Lead acetate trihydrate	PEKING CHEMICAL WORKE	861218