Synthesis of conjugated poly(acrylene)s with 1,2-type (η4-cyclobutadiene)cobalt moieties in the main chain

Abstract

The synthesis of polymers containing 1.2-type (η 4 -cyclobutadiene) cobalt moieties in the main chain (i.e., poly (cyclobutadienecobalt-1,2-duyl-alt-biphenyl-4,4'-diyl)s) is described. Dichloride monomers with (cyclobutadiene) cobalt moieties (i.e., (cyclopentadien-yl)[1,2 bis (4-chlorophenyl)-3, 4-bis (4-alkoxyphenyl)] cyclobutadiene cobalts were obtained by the reaction of (4-chlorophenyl)(4'-hydroxyphenyl) acetylene with (η 5 -cyclopentadienyl) bis (triphenylphosphine) cobalt (I) and chromatographic separation over silica gel of a pure 1,2-isomer followed by the alkylation of the hydroxy groups. The Ni(0)-mediated dehalogenative polycondensation of the 1,2-type monomer was carried out at 80°C in benzene under nitrogen to yield polymers which are soluble in common organic solvents. The number average molecular weights (M n ) of the resulting 1,2-type organocobalt polyarylenes were 8 000-13 600. The polymers with appropriate lateral alkyl chains were found to show a thermotropic liquid crystalline phase in the range of 58-184°C determined by differential scanning calorimetry and the optical measurement usinf the crossed polirazers.