Highly conjugated π-electron donors for organic metals: synthesis and redox chemistry of new 1,3-dithiole and 1,3-selenathiole derivatives

Abstract

The bis(1,3-dithiolium) dication salts 8a–c have been synthesised in three steps (31–51% overall yields) starting from 1,4-bis(bromomethyl)naphthalene, 9,10-bis(chloromethyl)anthracene and 4,4′-bis(chloromethyl)biphenyl, respectively. The bis(halogenomethyl) compounds 5 were converted into the dipiperidiniumbis(dithiocarboxylate) salts 6, which on alkylation with 3-chlorobutane-2-one yielded bis(dithioesters)7; cyclisation of 7 occurred on treatment with concentrated sulphuric acid to give dication salts 8. Dimethyl 1,3-dithiol-2-ylphosphonate 20, dimethyl 4,5-dimethyl-1,3-dithiol-2-ylphosphonate 21 and dimethyl 1,3-selenathiol-2-ylphosphonate 22 were treated with butyllithium in the presence of a range of carbonyl compounds and quinones, e.g., cyclopentanone, cyclohexanone, benzophenone, acetophenone, benzaldehyde, thioxanthen-9-one, anthraquinone, bianthrone and naphthacene-5,12-quinone to yield Wittig–Horner products, e.g., alkenes 26–34 and the anthracenediylidene derivatives 35, 36, 40–43 and 53. Unsymmetrical derivatives 37–39 were prepared in two steps as follows: anthrone reacted with 2-methylthio-1,3-dithiolium iodides 45 and 46 in pyridine-acetic acid to yield ketones 48 and 49 which were then treated with the Wittig–Horner reagents 23–25. Cyclic voltammetric data for the new tetrathiafulvalene, selenatrithiafulvalene and diselenadithiafulvalene derivatives 35–43and 53, show that these systems undergo two-electron redox behaviour which is observed as a single wave. Complexes of these donors with electron acceptors, e.g. 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), have been obtained, some of which are organic semiconductors.