The synthesis and characterization of new modified tetrathiafulvalenes (TTF), the S-position isomers of BEDT-TTF and EDT-TTF, are described. The synthetic strategy presented in this work is based on an efficient and unprecedented two-step sequence for the conversion of a vicinal bis(hydroxymethyl) functionality into a disulfide ring. Different routes are discussed in terms of efficiency for the synthesis of the symmetric S-position isomer of BEDT-TTF and that of EDT-TTF. Their electrochemical properties are combined with data obtained from UV/Vis spectroscopy and orbital calculations, and the electronic influence of peripheral sulfur atoms on the neutral and oxidized species is discussed. The introduction of these outer sulfur atoms at the periphery of the TTF core gives rise to specific intermolecular S...S interactions in the corresponding organic materials. Crystallographic studies of radical cation salts synthesized upon electrocrystallization clearly showed that the network obtained is dictated by the outer sulfur atoms, which are responsible for a characteristic and unprecedented "windmill" array.

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...

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Lohnende Ziele für die Synthese leitfähiger Materialien sind die Verbindungen 1–3, die das Tetrathiafulvalengerüst enthalten. 1 und ein Bis(methylsulfanyl)‐Analogon konnten jetzt synthetisiert werden; ihr Oxidationsverhalten ähnelt dem der Titelverbindung, deren Radikalkationensalze organische Supraleiter sind. Das TTF‐Gerüst von 1 ist nahezu planar, und die äußeren Schwefelatome sind am Aufbau des Netzwerks im Kristall beteiligt.

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