Using an iterative sequence of Wittig olefination, reduction, oxidation, and condensation of an active methylene group to carbonyl, it was possible to prepare a series of organometallic push-pull molecules [(COin which ferrocene is the donor element and a Fisher carbene moeity is the acceptor group. The molecular first hyperpolarizability β was determined by hyper-Rayleigh scattering experiments. The β values ranged from 110 × 10 -30 to 2420 × 10 -30 esu in acetonitrile, and they are among the highest reported for organometallic molecules so far. Electrochemical measurements are consistent with the push-pull nature of these compounds.# Dedicated to Professor D. Nasipuri on the occasion of his 75th birthday.

Reaction of Cp‘Co(PPh3)2, where Cp‘ = η5-cyclopentadienyl (Cp) or η5-n-hexylcyclopentadienyl (hexCp), with conjugated diacetylenes, RC⋮CAC⋮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. The polymers' bandgap energies (as estimated from visible spectra) are between 2.1 and 2.3 eV. Photoconductivity is observed for [−C4Me2{Co(hexCp)(PPh3)}−C6H4−] n (6e).

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