Synthesis, structure, and properties of hexaaryl[3]radialenes

A number of hexaphenyl[3]radialene derivatives were synthesized in modest to good yields by the reaction of tetrachlorocyclopropene with diarylmethyl anion followed by oxidation with oxygen. That the acidity of diarylmethane is higher than that of diphenylmethane is found to be an important factor for the successful synthesis. Lithiation and protonation of hexa(4-iodophenyl)[3]radialene thus obtained leads to the first synthesis of hexaphenyl[3]radialene. These hexaaryl[3]radialenes are stable, orange to red, crystalline substances. An X-ray crystallographic analysis of hexa(4-cyanophenyl)[3]radialene reveals a double three-bladed propeller conformation. The effects of substituents in the phenyl groups on their properties are most clearly seen in their electrochemical reduction potentials; among hexaphenyl[3]radialenes here obtained, hexa (4-nitrophenyl)[3]radialene (E-1(red) = -0.30 V, E-2(red) = -0.45 V) is found to be a good electron acceptor stronger than p-benzoquinone.