SYNTHESES, PROPERTIES, AND REDOX BEHAVIORS OF 7-PHENYL-1,2/3,4/5,6-TRIS(BICYCLO[2.2.2]OCTENO)TROPYLIUM ION AND THE DICATIONS COMPOSED OF 2 1,2/3,4/5,6-TRIS(BICYCLO[2.2.2]OCTENO)TROPYLIUM UNITS CONNECTED BY P-PHENYLENE AND M-PHENYLENE SPACERS

The stable carbodications composed of two tris(bicyclo[2.2.2]octeno)tropylium units connected by a p-phenylene (7) and a m-phenylene spacer (8) were synthesized, together with the corresponding monocation having a 7-phenyl substituent (6) as a reference compound, and their properties were fully characterized. The pK(R+) values of 6, 7, and 8 were determined in 50% aqueous acetonitrile to be 12.0, 11.5, and 10.4, respectively. The 7-phenyl substituent, which is supposedly nearly perpendicular to the tropylium ring, destabilizes the cation by 1 pK unit. The two cation units at the p-phenylene positions in 7 were neutralized simultaneously, but those in 8 were neutralized stepwise; the pK(R+) value for the half-neutralized monocation was 12.2. Upon one-electron reduction monocation 6 gave a stable free radical persisting in solution at room temperature. p-Phenylene-connected dication 7 did not give any radical species but instead gave a closed-shell hydrocarbon upon one-step, two-electron reduction. In the case of m-phenylene-connected dication 8, two very closely spaced reduction steps were observed upon cyclic voltammetry, and the resulting fully reduced species was identified as a triplet diradical by low-temperature ESR.