Synthesis and electrochemical properties of new l,3-dithiol-2-ylidene derivatives.
The π-electron donor system 9-(l,3-dithiol-2-ylidene)thioxanthene has been synthesised via Homer-Wadsworth-Emmons reactions of l,3-dithioI-2-phosphonate ester reagents with thioxanthen-9-one. The electrochemistry of a range of derivatives shows a single, two-electron oxidation wave, which is quasi-reversible. X-Ray crystal analysis reveals a folded structure. Compound 33c has proved to be a key building block which via lithiation chemistry has provided the hydroxymethyl derivative 37 and hence the synthesis of derivatives with covalently attached fluorenone, dicyanomethylenefluorene and PTM (4-[bis(2,3,4,5,6-pentachlorophenyl)methyl]-2,3,5,6-tetrachlorobenzoyl chloride radical) as electron acceptor substituents has been achieved. Electrochemical, spectroscopic and spectroelectrochemical studies have revealed the presence of intramolecular interactions in these compounds. 9-(4-Iodo-5-methyl-1,3-dithiol-2-ylidene)thioxanthene has been synthesised and shown to undergo clean metal-catalysed cross-coupling reactions under Suzuki and Sonogashira conditions, which is unusual for l,3-dithiol-2-ylidene derivatives. Aldehyde functionality has been attached to the 9-(l,3-dithiol-2-ylidene)thioxanthene core and reacting these aldehyde reagents with C(_60) and sarcosine gave covalent 9-(l,3-dithiol-2-ylidene)thioxanthene- C(_60) 1:1 diad molecules, and the analogous 2:1 adducts. A second series of compounds, with more extension of the π-system, eg compound 66a, has been synthesised and characterised by X-ray crystallography, a range of spectroscopic studies and by epr and electrochemistry.