For the synthesis of π-conjugated polymers containing heteroatoms, reactive organometallic polymers may serve as useful synthetic precursors. We have been working on the synthesis of titanacyclopentadiene-containing polymers by the reaction of aromatic diynes and a low-valent titanium complex. Considering the advantages of fused ring systems such as more effective π-conjugation and narrower HOMO-LUMO gaps, here we describe the synthesis of titanacycles with fused ring systems and polymers containing the corresponding units.<br/>A titanafluorene derivative (i.e., dibenzotitanacyclopentadiene) was obtained as orange crystals by the lithiation of 2,2’-diiodobiphenyl using <i>n</i>-BuLi followed by the reaction with titanocene dichloride. Likewise, a dithienotitanacyclopentadiene, in which two thiophene rings are fused with the titanacyclopentadiene unit, was obtained as green crystals from 3,3’-dibromobithiophene. Arylene dihalide monomers possessing the corresponding units were also obtained with modifications and were subjected to the Sonogashira-Hagihara coupling polycondensation with 1,4-di(octyloxy)-2,5-diethynylbenzene in the presence of a palladium catalyst to give the objective poly(arylene ethynylene)s containing titanafluorene and dithienotitanacyclopentadiene units in the π-conjugated main chain. Unlike titanacyclopentadiene-containing, the fused tianacycle-polymers relative proved to be stable under air at ambient temperature that provided us a chance to explore functions and applications of the polymers. The unique optical and electronic properties of the resulting polymers will also be described.

Synthesis and applications of unique π-conjugated polymers containing π-extended fused metallacycle units

ACS Spring Meeting 2021

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