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Reaction of Cp‘Co(PPh3)2, where Cp‘ = η5-cyclopentadienyl (Cp) or η5-n-hexylcyclopentadienyl (hexCp), with conjugated diacetylenes, RC⋮CAC⋮CR, where A = p-phenylene, p-fluorophenylene, p-2,5-difluorophenylene, or 4,4‘-biphenylene and R = H or Me affords new organometallic polymers, [−C4R2{CoCp‘(PPh3)}−A−]n (1−6) involving linearly π-conjugated chains. The polymers are insoluble when Cp‘ = Cp but soluble in common organic solvents when Cp‘ = hexCp. It is suggested by the results of reactions of (hexCp)Co(PPh3)2 with PhC⋮CH and PhC⋮CMe that stereoregularity favorable to π-conjugation, i.e., connection of cobaltacyclopentadienylene moieties at 2,5 position is higher when R = Me compared to when R = H. The cobaltacyclopentadiene polymers undergo quasi-reversible oxidation and irreversible reduction at low temperatures. The oxidation potential is not significantly changed, but the reduction potential shifts considerably in the positive direction for the polymers compared to monomeric cobaltacyclopentadienes. T...

Reactions of [CpCo(PPh3)2](Cp=η5-cyclopentadienyl) with conjugated diacetylenes were investigated in terms of the synthesis of π-conjugated organometallic polymers. The reaction of an α,β-diyne, PhCCCCPh, gave three geometric isomers of dialkynylcobaltacyclopentadienes, 1a-c, and an insoluble polymeric product, 1d. A 2,4-dialkynyl complex, 2, and a 2,5-dialkynyl complex, 3, were obtained solely from Me3SiCCCCSiMe3 and MeCCCCMe, respectively. 1,1′-Bis(trimethylsilylethynyl)-4,4′-biphenyl afforded two isomers of 1,3-dialkynylcyclobutadiene complexes, 4a and 4b. The stability of the one-electron oxidized forms of the cobalacyclopentadiene and cyclobutadiene complexes was examined by cyclic voltammetry.

A π-conjugated organometallic polymer with cobaltacyclopentadiene units was synthesized by successive metallacyclization reactions of diacetylene, 4,4′-diethynylbiphenyl with CpCo(PPh 3 ) 2 . The yield, infrared and UV-VIS spectra, and thermal properties depend on the synthetic conditions such as the mol ratio of the diacetylene to CpCo(PPh 3 ) 2 , solvent and reaction temperature. The electrical conductivity of the Co complex polymer is around 10 −9 S cm −1 at room temperature.

A new π-conjugated organometallic polymer of which framework is in part composed of cobaltacyclopentadienes has been synthesized by a metallacycle formation reaction of CpCo(PPh3)2 with 4,4′-diethynylbiphenyl. The polymer, poly(4,4′-biphenylene 2,5-cobaltacyclopenta-2,4-dienylene) has a strong absorption band around 500 run, and is oxidized at +0.306 V vs. Ag/Ag+ in dichloromethane and reduced at −1.8 V in acetonitrile.