Novel Electron Acceptors Bearing a Heteroquinonoid System. I. Synthesis and Conductive Complexes of 5,5′-Bis(dicyanomethylene)-5,5′-dihydro-Δ2,2′-bithiophene and Related Compounds

Novel electron acceptors bearing a heteroquinonoid system, 5,5′-bis(dicyanomethylene)-5,5′-dihydro-Δ2,2′-bithiophene, its 3,3′-dichloro, 3,3′-dibromo, and 3,3′,4,4′-tetrabromo derivatives, and 5,5″-bis(dicyanomethylene)5,5″-dihydro-Δ2,2′:5′,2″-terthiophene were synthesized by the action of tetracyanoethylene oxide or by Pd(0)-catalyzed substitution reactions with sodium dicyanomethanide on the corresponding α,α′-dihalogenoheteroaromatics. They showed very small on-site Coulomb repulsion as expected, and afforded several highly conductive molecular complexes with electron donors such as hexamethylenetetratellurafulvalene.