Studies of the First S‐Position Isomer of Bis(ethylenedithio)tetrathiafulvalene

Abstract

Over the last two decades chemical modifications of the tetrathiafulvalene (TTF) framework[" have been developed to favor enhanced dimensionality in the related charge-transfer salts. ['] One of the most promising strategies consists of introducing additional sulfur atoms at the periphery of the TTF skeleton. In particular, the famous bis(ethy1enedithio)-TTF (BEDT-TTF) is known to form superconducting salts with the highest T, yet observed for that series;[3, 41 all of them exhibit two-dimensional (2-D) character (for example p and K phases). The prominent role of the outer sulfur atoms has also been recognized in highly conducting or superconducting salts of TTF derivativesF5 -71We therefore focused our attention on the peripheral S-position isomers of BEDT-TTF and (ethy1enedithio)-TTF (EDT-TTF) A, B, and C as new synthetic targets. Our general synthe-A 0 Ir tic strategy for these is based on 1) conversion of the appropriate vicinal bis(hydroxymethy1)-TTF 1 [' I into its corresponding, new bis(sulfanylmethy1)-TTF 2 and 2) disulfide bridge formation by selective, intramolecular, oxidative ring closure. We present here a straightforward access to new 3a and 3b by the steps shown in Scheme 1 and report on their n-donor ability. The latter is demonstrated by preliminary electrooxidation experiments with generation of the radical cation salts 3a.PF6 and 3a. ClO,, whose X-ray structures are presented together with that of neutral 3a. 4a (59%) 4b (M)%) NaBH4, ZnCI, A, THF Method CH+COCH, AorB CH2SCOCH3 CHzOH f --COMMUNICATIONS 878 VCH Verlug~ge~eilschuft mhH 0-69451 Weinheim. 1997 057#-0833~97~3608-0878$17 SO+ 5010 Angew Chem Int Ed Engl 1997, 36 No 8 Sa, b I DIBAI-H -78°C. CH,CI, 28 (91%) 2b (96%) 38 R,R=SCH3 3b R-R = SCHzCH2S Scheme 1. a: R, R = SCH,; b: R-R = SCH,CH,S. Synthesis of the disulfide TTFs 3 from bis(hydroxymethy1)-TTFs 1. Method A . DEADIPPh,. CHJOSH, THF, 5a: 58%. Method B: Me,NCH(OEt),, CH,COSH, A, CH,CI,. 5a: 59%. 5b: 60%.The starting materials la and Ib were prepared by our standard procedure.Iac1 Cross-coupling (with P(OMe),) of two 2thioxo-I ,3-dithiole or 2-oxo-l,3-dithiole moieties afforded the unsymmetrical 2,3-dimethoxycarbonyl derivatives 4a and 4b. Reduction of the ester functionalities gave la and Ib in 83 and 70 YO yield, respectively. Although the obvious reaction sequence starting from 1 (tosylation or bromination followed by nucleophilic displacement with sodium hydrosulfide) failed,"] the Mitsunobu reaction["] could be used. Thus, a one-pot conversion into 5a was achieved by treatment of la with the diethyl azodicarboxylate/triphenylphosphane (DEAD/PPh,) complex and subsequent in situ displacement of the resulting leaving group with thiolacetic acid, as described by Volante." However, in the case of compound Ib this procedure was not convenient due to the well-known sensitivity of the ethylenedithio bridge with respect to bases."'] The hydroxy group was therefore activated with N,N-dimethylformamide dialkylacetal. [' 31 By treatment of Ib with excess thiolacetic acid and N,Ndimethyl...

Synthesis of Electro-active Compounds Suitable for Adsorption on Metal Surfaces

“…6 The preparative methods used for TTF compounds of these types are illustrated by the conversion of 39, by way of 40, into 41, 42 and 43 (Scheme 10). 29 Reduction of the diester with sodium borohydride and zinc chloride gives the diol 40 which is condensed with thioacetic acid under Mitsunobu conditions to afford 41. This can be either reduced to the dithiol 42 using diisobutylaluminium hydride or converted directly into the dihydro-1,2-dithiin 43 by borohydride reduction followed by treatment with ammonium chloride.…”

“…The same method was also used to prepare the unsubstituted analogue 44 (Scheme 11), 30 For the ethylenedithio-TTF compounds 45 and 46 the same procedures were also used with the important exception that the Mitsunobu step was replaced by condensation with thioacetic acid in the presence of dimethylformamide diethyl acetal. 29,30 This method was also employed in the preparation of the symmetrical TTF-bis(dihydro-1,2-dithiin) 47 which is isomeric both with 46 and the more familiar bis(ethylenedithio)TTF or "ET". 31 Despite their obvious potential for surface adsorption, such studies on these compounds do not appear to have been carried out.…”

Syntheses and properties of a new series of tetrathiafulvalene derivatives incorporating fused ethyleneoxymethylene and ethylenethiomethylene units, and their charge–transfer complexes

“…In the case of the BET-TTF donor having an outer ethylenethio group of five-membered rings, the mean folding angles are 178 [18]. In the case of the S-position isomer of DMTEDT-TTF, 4,5-dimethylthio-4 0 ,5 0 -(2,3-dithiabutane-1,4-diyl)-tetrathiafulvalene, the outer six-membered ring is highly distorted around the SÀ ÀS bridge and adopts a half-chair conformation [25]. The outer ETM framework of this compound is analogous to that of the S-position isomer of DMTEDT-TTF.…”

A Novel Tetrathiafulvalene Building Block

“…This type of tetrathiafulvalene derivatives are of considerable current interrest due to its peripheral S-position isomerism with ethylenedithiotetrathiafulvalene. [17][18][19]…”