1. Field of the Invention
Preparations of substituted tetraselenafulvalenes from reactions of carbon diselenide with various acetylenic compounds are well known. Of particular interest herein is a one-step method for synthesis of substituted tetraselenafulvalenes from reactions of carbon diselenide with an acetylenic compound under high pressure conditions.
2. State of the Art
Recent findings of the unusual electronic properties of complexes of tetraselenafulvalent (TSeF) have generated increased interest in new synthetic routes for preparation of TSeF and substituted TSeF analogue-compounds. It has been found, for example, that certain substituted TSeF compounds, such as tetramethyltetraselenafulvalene, can complex with inorganic anions, such as PF.sub.6.sup.- and AsF.sub.6.sup.-, to form crystalline charge-transfer salts. These salts, in which the substituted TSeF is characterized as the electron-donor cation, exhibit metallic properties over a wide temperature range and reportedly have electrical conductivities 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 TSeF and substituted TSeF compounds involve multi-step synthetic routes which typically produce TSeF or substituted TSeF compounds in low yields or in relatively impure form.
For example, fulvalene compounds containing selenium in the ring system have been synthesized by reaction of sodium acetylide with carbon diselenide in the presence of selenium metal to provide 1,3-diselenole-2-selone. A subsequent coupling reaction of this selone compound with trimethyl phosphite produced a selenium-containing fulvalene compound in an overall maximum yield of 20 percent (Engler et al., J. Amer. Chem. Soc., 96, 7376 (1974)).
Tetraselenafulvalene has been prepared by reaction of dimethyl acetylenedicarboxylate with ethylene triselenocarbonate to produce a diester-substituted selone compound, which compound when treated with triphenylphosphine yielded tetraester-substituted selenafulvalene. Subsequent treatment of this fulvalene compound with lithium bromide in the presence of hexamethylphosphoramide provided tetraselenafulvalene in about 23 percent overall yield (Lakshmikanthan et al., J. Org. Chem., 41, 882 (1976).
U.S. Pat. No. 3,941,809 to Kaplan et al., describes a selenium-containing fulvalene compound prepared by a multi-step method involving firstly reduction of a 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 or four selenium atoms, depending upon the starting organic halide.