1. Field of the Invention
Preparations of sulfur-and-selenium-containing fulvalenes are well known. Of particular interest herein is a one-step method for synthesis of substituted sulfur-and-selenium-containing fulvalenes from reactions of an acetylenic compound with sulfide-and-selenide starting materials under high pressure conditions.
2. State of the Art
Recent findings of the unusual electronic properties of complexes of certain sulfur-and-selenium-containing fulvalenes have generated increased interest in new synthetic routes for preparation of these fulvalene compounds. Certain fulvalene compounds having sulfur and selenium atoms in the fulvalene rings can be used to prepare crystalline charge-transfer salts. For example, in IBM German Offen. No 2,739,584 (1978), there is described a charge-transfer salt comprised of dithiadiselenafulvalene and tetracyano-p-quino-dimethane. Such salt, in which the fulvalene compound is characterized as the electron-donor cation, exhibits metallic properties over a wide temperature range and reportedly has electrical conductivity among the highest of known organic materials.
The superior electrical properties of these salts, so-called "organic metals", make the salts particularly likely candidates for many solid-state or physical-electronics applications. In such applications, materials of very high purity are usually required. Known preparations of sulfur-and-selenium fulvalenes and substituted sulfur-and-selenium fulvalene compounds involve complicated multi-step synthetic routes which typically produce these fulvalene compounds in low yields or in relatively impure form.
One lengthy method for making fulvalene compounds containing sulfur and selenium in the five-membered ring system is described in U.S. Pat. No. 3,941,809 to Kaplan et al. These fulvalene compounds are prepared by a multi-step method involving firstly reduction of a sulfur-and-selenium-containing five-member ring organic halide to its partially-hydrogenated derivative, which derivative is reacted with anhydrous fluoboric acid to provide a fluoborate, which fluoborate is then deprotonated in the presence of an alkyl tertiary amine to yield a fulvalene compound containing two sulfur and two selenium atoms.
In U.S. Pat. No. 4,028,346 to Engler et al, a two-step synthesis is described for preparation of sulfur-selenium fulvalenes. This method involves reacting sodium acetylide with carbon diselenide in the presence of sulfur to provide 1,3-thiaselenole-2-selone. A subsequent coupling reaction of this selone compound in the presence of trimethylphosphite produces dithiadiselenafulvalene in an unreported yield. In a later publication, however, Lakshmikantham and Cava [J. Org. Chem., 45, 2632 (1980)] report that the Engler type two-step synthesis provides an overall yield of dithiadiselenafulvalene of less than one percent. This later publication then describes an improved route for synthesis of dithiadiselenafulvalene by first converting 1,2,3-selenadiazole to 1,3-thiaselenole-2-thione, which thione is then converted by conventional methods to 1,3-thiaselenole-2-selone and then by coupling reaction to dithiadiselenafulvalene. Overall yield of this fulvalene is only about 24 percent, however.