ISOLATION AND PROPERTIES OF HYDROCARBON SALTS

Four solid hydrocarbon salts 2.1, 3.1, 4.1, and 5.1 consisting of Kuhn’s anion, tris(7H-dibenzo[c,g]-fluorenylidenemethyl)methide ion (C48H39-, 1) as a carbanion moiety, and tris[l-(5-isopropyl-3,8-dimethyl-azulenyl)]cyclopropenylium (C48H51+, 2), tricyclopropylcyclopropenylium (C12H15+, 3), l-[(2,3-diphenylcyclo-prop-2-enylidene)methyl]-2,3-diphenylcyclopropenylium (C31H21+, 4), or 1,3,5-tricyclopropyltropylium (C16H19+ , 5) as a carbocation moiety were prepared and their properties investigated. The salt formation was proved by satisfactory elemental analyses, IR spectra (KBr disk), and UV-vis (DMSO) spectra, the spectra consisting of those of the respective cations and Kuhn’s anion superimposed. Essentially complete ionization of the hydrocarbon salts 2.1 and 3.1 in DMSO was also evidenced by electric conductivity measurements. In chloroform solutions, 2.1 and 4.1 are unstable and evaporation of the solvent gave covalent hydrocarbons whose structures were not wholly determined. Meanwhile, 3.1 is converted into a covalent hydrocarbon 3–1 in chloroform whose structure was determined by 1H NMR spectroscopy. Chilling of the chloroform solution of 3–1 or evaporation of the solvent, however, regenerates the original hydrocarbon salt 3.1. Thus, 3–1 is the first covalent hydrocarbon that is existing only in solution. The hydrocarbon salt 5.1 also forms covalent hydrocarbon 5–1 in chloroform and regenerates 5.1 on immediate evaporation of the solvent; however, 5–1 gradually generates radicals 5. and 1. In THF 5.1 undergoes both coordination and single electron transfer, affording the ionic, radical, and covalent species coexisting in equilibria. This behavior provides the first example showing that the three types of elementary organic species (ions, radicals, and a covalent compound) coexist in equilibria. The occurrence of single electron transfer from 1 to 5 is attributed to the considerably greater electron affinity of 5 than 2, 3, and 4. © 1990, American Chemical Society. All rights reserved.