Conjugated organometallic polymers containing Vollhardt's cyclobutadiene complex: Aggregation and morphologies

Organometallic polymers were prepared by acyclic diyne metathesis (ADIMET) or by Pd-catalyzed coupling of 1,3-diethynylcyclobutadiene(cyclopentadienyl )cobalt with a suitably substituted diiodobenzene. The polymers obtained by Heck coupling show a degree of polymerization (P-n) of 20-60. The monomers for ADIMET were made by the Pd-catalyzed coupling of [1,3 -bis (trimethyls ilylethynyl) -2,4bis(trimethylsilyl)cyclobutadiene] (cyclopentadienyl)cobal t to 1-bromo-2,5-dialkyl-4-propynylbenzenes in the presence of KOH in yield s of 40 - 48 %. The monomers carry hexyl, ethylhexyl, and (S)-3,7-dimethylo ctyl side chains. Polymerization of the propynylated monomers furnishes org anometallic polymers with a P-n of up to 230 arylene-ethynylene units. The polymers were fully characterized by polarizing microscopy, transmission el ectron microscopy, circular dichroism, differential scanning calorimetry, a nd X-ray diffraction (XRD). They show nematic, lyotropic liquid crystalline phases as well as chiroptical properties from which aggregation in poor so lvents and in the solid state can be concluded. Lamellar or irregular honey comb-shaped morphologies in these organometallic polymers can be detected b y electron microscopy.