SYNTHESIS OF POLY(ARYLENE COBALTACYCLOPENTADIENYLENE)S, A NEW CLASS OF ORGANOMETALLIC PI-CONJUGATED POLYMERS, BY METALLACYCLING POLYMERIZATION AND THEIR PHYSICAL-PROPERTIES

Reaction of Cp'Co(PPh(3))(2), where Cp' = eta(5)-cyclopentadienyl (Cp) or eta(5)-n-hexylcyclopentadienyl (hexCp), with conjugated diacetylen es, RC=C-A-C=CR, where A=p-phenylene, p-fluorophenylene, p-2,5-difluor ophenylene, or 4,4'-biphenylene and R=H or Me affords new organometall ic polymers, [-C(4)R(2){CoCp'(PPh(3))}-A-](n) (1-6) involving linearly pi-conjugated chains. The polymers are insoluble when Cp' = Cp but so luble in common organic solvents when Cp' = hexCp. It is suggested by the results of reactions of (hexCp)Co(PPh(3))(2) with PhC=CH and PhC=C Me that stereoregularity favorable to pi-conjugation, i.e., connection of cobaltacyclopentadienylene moieties at 2,5 position is higher when R=Me compared to when R=H. The cobaltacyclopentadiene polymers underg o quasi-reversible oxidation and irreversible reduction at low tempera tures. The oxidation potential is not significantly changed, but the r eduction potential shifts considerably in the positive direction for t he polymers compared to monomeric cobaltacyclopentadienes. The polymer s' bandgap energies (as estimated from visible spectral are between 2. 1 and 2.3 eV. Photoconductivity is observed for [-C(4)Me(2){Co(hexCp)( PPh(3))}-C6H4-](n) (6e).