Organic Metals and Superconductors: Facile Synthetic Methodologies Bypassing Coupling and Chromatography
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SCHEME 1
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Mat. Res. Soc. Symp. Proc. Vol. 488 © 1998 Materials Research Society
Presently, the use of ITF as a precursor to extended donors is hampered by a number of limitations: (1) TTF is expensive and published syntheses are tedious 9 (2) The disulfide electrophiles used must be soluble in THF or Et 2 0, and yields are very dependent on the extent of electrophile solubility, (3) As a result of the difficulty of sulfur insertion and subsequent intramolecular alkylation with 1,2-dibromoalkanes, a facile conversion of T17F into BEDT-TFand other capped tetrathiafulvalene tetrathioles (TTFIT's) has not been realized, (4) The capping2 of tetrakis(chalcogeno)TTF tetraanions requires the alkyl dihalide to be primary (SN mechanism) thereby excluding aromatic caps, and (5) Tedious purification methods are often employed. 3 A new synthetic method eliminating these limitations accompanied by high yields would invariably be useful for the syntheses of known organic metals and superconductors as well as new materials. SYNTHETIC METHOD As has been previously reported, TIN can be used as a precursor to substituted TrF's or it can be functionalized to give substituted TTN.10 , 11, 12 A simple synthesis of TTN and its conversion to TTF has been reported. 12 Building on prior synthetic routes to alkylthio-TTF's from disulfides, unsymmetric disulfides have been synthesized; each incorporating an ester leaving group. Upon nucleophilic attack of tetralithiated TTF or isomerized tetralithiated TTN onto 4 equivalents of a disulfide, tetrakis(thioalkyl)TTF's and tetrakis(thioaryl)TrF's are produced along with 4 equivalents of ethanol and 4 equivalents of carbon oxysulfide (scheme 2). The simple byproducts facilitate workup. Disulfide formation is based on the chemistry of Brois, who has utilized alkoxycarbonylsulfenyl chlorides and a variety of thiols to produce ester alkyl disulfides (EtOC(O)S-S'R) which selectively yield unsymmetric disulfides (R'-S-S-R") upon reaction with one equivalent of a different thiol (R"SH). 13 The utility of EtOC(O)S-S'R disulfides can be seen when the symmetric disulfide RS'-S'R is not soluble or poorly soluble in THF or Et 2 0.
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