1,1,4,4-tetra(2-furyl, 2-thienyl, and 2-selenienyl)butatrienes: Synthesis, properties, and molecular structures

Tetra(2-furyl, 2-thienyl, and 2-selenienyl)butatrienes and their derivatives have been prepared by dimerization of ate-type complexes derived from the corresponding 1,1-dichloro-2,2-diarylethenes using appropriate copper complexes in moderate to high yields. These new butatrienes are relatively stable crystalline substances with intense absorption bands at long wavelengths. The electronic properties of the substituents at the 5-position of aryl groups remarkably influence the wavelength of the longest absorption and the pi-electron distribution of butatriene moiety. Their redox potentials, measured by cyclic voltammetry, have higher amphoteric redox properties than those of tetraphenylbutatriene. The crystal structures of tetrakis(5-trimethylsilyl)-substituted derivatives show the following two features: (1) the thiophene and selenole derivatives have pseudo-D-2 structures, while the furan derivative has a C-2 symmetric structure probably due to the counterbalance between the energy of conjugation and the nonbonded chalcogen-chalcogen interaction; (2) the central double bonds of these butatrienes are considerably short.