Ferrocenecarboselenoic Acid: Synthesis and Some Reactions

The first ferrocenecarboselenoic acid was synthesized and characterized. The existence of tautomeric equilibrium between the selenol (FcCOSeH) and selenoxo forms (FcCSeOH) in polar solvents was proven by 1H-, 13C- and 77Se-NMR spectra. The selenoxo form exists predominantly in a polar solvent at low temperature below –70 °C. Treatment of this acid with lithium, sodium, and potassium hydrides and with rubidium and cesium fluorides gave the corresponding alkali metal ferrocenecarboselenoates in quantitative yields. Treatment with 4-methylphenyl isocyanate at room temperature led to ferrocenoyl 4-methylphenylcarbamoyl selenide FcCOSeC(O)NHC6H4Me-4 in high yield. A similar reaction with phenyl isothiocyanate formed a mixture of FcCOSeC(S)NHPh and FcCOSeC(SH)=NPh in moderate to good yield. The carboselenoic acid readily reacted with piperidine to give piperidinium ferrocenecarboselenoate in good yield. Air oxidation of this selenoic acid afforded diferrocenoyl selenide as a major product along with diferrocenoyl diselenide. The structures of the selenide (FcCO)2Se and diselenide (FcCOSe)2 were examined by single-crystal X-ray analysis.