Synthesis of Poly(arylene cobaltacyclopentadienylene)s, a New Class of Organometallic π-Conjugated Polymers, by Metallacycling Polymerization and Their Physical Properties

Abstract

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).

Regioselective synthesis and electrochemical properties of π-conjugated cobaltacyclopentadiene oligomer and polymer complexes

“…These results are similar to those for previously reported cobaltacyclopentadiene complexes with no halide groups. 2,4,11, 12 The E ЊЈ value and the reversibility of the oxidation reaction of the polymer were almost consistent with those of oligomers [Fig. 4(b), (c)].…”

Dibenzometallacyclopentadienes, boroles and selected transition metal and main group heterocyclopentadienes: Synthesis, catalytic and optical properties

“…The only other example of this type of compound is an osmium complex, formed by reaction of [Os(en) 2 (H 2 O)(H 2 )] with 2,4-hexadiyne, producing the 2,5-diethynylmetallacycle exclusively [83]. [86,87] and "ZrCp 2 " [88].…”

“…Nishihara and co-workers were the first group to prepare and characterize polymers of this type, successfully isolating a number of poly(arylene cobaltacyclopentadienylene)s [87]. They found that use of Cp as a ligand on Co resulted in insoluble polymers.…”

Organometallic Polymers of the Transition Metals

“…Polymers containing cobaltacyclopentadiene groups in their backbones have also been prepared via metallacycling polymerization reactions. [285][286][287][288]335,336] 8 Metal-Metal Bonded Systems Puddephatt and coworkers have reported the reaction of a platinum complex with diacetylides and diisocyanides to produce oligomers and polymers containing Pt-Pt bonds in their backbones. [337] While reactions with acetylides produced oligomers with low solubility, the IR spectra of the polymers shown in Scheme 76 did not show the presence of uncoordinated isocyanide groups.…”