Synthesis of conjugated poly(acrylene)s with 1,2-type (eta(4)-cyclobutadiene)cobalt moieties in the main chain

The synthesis of polymers containing 1,2-type (eta(4)-cyclobutadiene)cobalt moieties in the main chain (i.e., poly(cyclobutadienecobalt-1,2-diyl-alt-b iphenyl-4,4'-diyl)s) is described. Dichloride monomers with (cyclobutadiene )cobalt moieties (i.e., (cyclopentadienyl)[1, 2-bis(4-chlorophenyl)-3, 4-bi s(4-alkyoxphenyl)]cyclobutadiene cobalts were obtained by the reaction of ( 4-chlorophenyl)(4'-hydroxyphenyl)acetylene with (eta(5)-cyclopentadienyl)bi s(triphenylphosphine)cobalt(I) and chromatographic separation over silica g el of a pure 1,2-isomer followed by the alkylation of the hydroxy groups. T he Ni(0)-mediated dehalogenative polycondensation of the 1,2-type monomer w as carried out at 80 degrees C in benzene under nitrogen to yield polymers which are soluble in common organic solvents. The number average molecular weights ((M) over bar(n)) of the resulting 1,2-type organocobalt polyarylen es were 8000-13600. The polymers with appropriate lateral alkyl chains were found to show a thermotropic liquid crystalline phase in the range of 58-1 84 degrees C determined by differential scanning calorimetry and the optica l measurement using the crossed polarizers.