1,8-diketone ring closure reaction to the synthesis of BEDT-TTF derivatives

Abstract

For the past 25 years there has been considerable interest in crystalline organic materials that possess unusual electronic and magnetic properties. This is due to metallic behaviour of its radical cation salts with mono anions and electron acceptors such as TCNQ, which exhibit semiconducting, conducting and superconducting properties. The most widely studied derivative, bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) which shows superconducting property, has the highest critical temperature, Tc=12.8 K, with K-(BEDT-TTF)Cu[N(CN)2Br]. The aim of this work is to synthesise new derivatives of bis(ethylenedithio)tetrathiafulvalene. Use of Lawesson's reagent (LR) and Phosphoruspentasulfide ($P_4S_{10}$) leads such a ring formation via chemical conversion of carbonil groups to thiocarbonyls, which is called 1,8-diketone ring closure reaction. In both cases, with LR and $P_4S_{10}$, the reaction resulted in the formation of six membered 1,4-dithiin and five-membered thiophene rings along with the side products. The dithiins and the thiophenes was coupled with the readily available 4,5-di(methylsulfanyl)-1,3-dithiol-2-one in neat triethylphosphite at $110^circ C$ under nitrogen atmosphere. A successful column chromatography achieved their separation as the crosscoupled and selfcoupled products. The cross coupled and self coupled products were characterized by NMR ($^1H, ^{13}C $), MASS and Elementel Analysis. Oxidation potensials of organosulfur donors, which are the coupled products were measured by cyclic voltammetry and are compared with data for ET.

Özet

TTF türevlerinin sentezine yönelik çalışmalar son yıllarda artış göstermiştir. Günümüzde "tetratiyafulvalen" sınıfı organik süperiletkenlerde süperiletkenlik özelliği en yüksek 12.8K'de bis(etilenditiyo)tetratiyafulvalen (BEDT-TTF veya ET) 'nin Cu[N(CN)2]Cl ile yaptığı "charge-transfer" tuzu ile gözlenmiştir. Süperiletkenlik; elektrik akımının iletilmesi sırasında direncin yok olması ve materyalin üzerine uygulanan manyetik alanın süperiletken tarafından itilmesi (Meissner etki) ile açıklanmaktadır. Bu çalışmanın amacı 1,8-diketonlardan Lawesson's reaktantı ve $P_4S_{10}$ ile halka kapama reaksiyonu sonucu 1,4-ditiyin ve tiyofen elde etmektir. Ph, 4-$CH_3OPh$, 4-BrPh ve $CH_3$ gibi fonksiyonel gruplar taşıyan bu maddeler 4,5-di(methylsulfanyl)-1,3-dithiol-2-one ile birleştirilerek üç ürün elde edilmiştir. Bu ürünlerin yapısı NMR( $^1H, ^{13}C $), MASS ve Elementel Analiz ile karakterize edilmiştir.