Annulenoid tetrathiafulvalenes: 5,16-bis(1,3-benzodithiol-2-ylidene)-5,16-(dihydrotetraepoxy- and 5,16-bis(1,3-benzodithiol-2-ylidene)-5,16-dihydrotetraepithio[22]annulenes(2.1.2.1)

The title compounds are among the first tetrathiafulvalenes with annulene s pacers, here with tetraepoxy-[22]annulene(2.1.2.1) (see 3a), tetraepithio[2 2]annulene(2.1.2.1) (see 3b), and diepithiodiepoxy[22]annulene(2.1.2.1) (se e 23) units. The annulenoid tetrathiafulvalenes 3a and 3b are prepared by c yclizing McMurry coupling of the 5,5'-(1,3-benzodithiol-2-ylidenemethylene) bis[furan- or thiophene-2-carbaldehydes] (8a or 8b, resp.) or by Wittig rea ction of (1,3-benzodithiol-2-yl)tributylphosphonium tetra fluoroborate (13b ) with tetraepoxy[22]annulene(2.1.2.1)-1,12-dione 20 (formation of 3a) or d iepithiodiepoxy[22]annulene(2.1.2.1)1,12-dione 22 (formation of 23). The an nulenoide tetrathiafulvalene 3a is obtained as a mixture of the isomers (E, E)- and (Z,Z)-3a. At 130 degrees, (Z,Z)-3a rearranges quantitatively into t he (E,E)-isomer. Isomer (E,E)-3a is a dynamic molecule, where the (E)-ethen e-1,2-diyl bridges rotate around the adjacent sigma -bonds, The tetraepithi oannulene derivative 3b as well as 23 only exist in the (Z,Z) -configuratio n. The oxidation of (E,E/Z,Z)-3a with Br-2 yields the annulene -bridged tet rathiafulvalene dication (E,E)-3a(Ox), while with 4,5-dichloro-3,6-dioxocyc lohexa-1,4-diene-1,2-dicarbonitrile (DDQ) obviously only the radical cation 3a(Sem) is formed, which belongs to the class of cyanine-like violenes. Th e annulenoide tetrathiafulvalenes 3b and 23, which exist only in the (Z,Z) -configuration, obviously for steric reasons, cannot be oxidized by DDQ. El ectrochemical studies are in agreement with these results.