Synthesis of Pyrrole‐Based Poly(arylenevinylene)s via Co‐Catalyzed Hydroarylation of Alkynes

Abstract

Polyaddition via the Co‐catalyzed hydroarylation of 1‐(2‐pyrimidinyl)pyrrole with aromatic diynes affords poly(arylenevinylene)s under mild conditions. This reaction avoids production of stoichiometric amounts of by‐products. Although structural analysis of the obtained polymers reveals the presence of 1,1‐vinylidene unit, switching the counter anion of the Co catalyst and steric hindrance of the diyne monomers improves the regioselectivity of the polymers. When a catalyst with bulky counter anions is used for the reaction of less hindered diyne monomers, 1,2‐vinylene linkages are formed dominantly over 1,1‐vinylidene linkages (93:7). The effect of the regioselectivity of the polymer on the optical and semiconducting properties is also evaluated.

Regioselective Synthesis of Thiophene-Based Poly(arylenevinylene)s via Co-Catalyzed Hydroarylation Polyaddition

“…Thus, the steric hindrance of the substituents such as the methyl or fluorine groups adjacent to the alkyne moieties prevents the migratory insertion of the alkyne into the Co-thiophene intermediates. , The structural analyses of synthesized PAVs were conducted using NMR and MALDI-TOF-MS (Supporting Information). The 1 H NMR spectrum of Pab showed a trace amount of the 1,1-vinylidene unit at approximately 1% (Figure S14), which was attributed to the steric hindrance of the 9,9-alkyl chains of the fluorene unit . In contrast, the 1 H NMR spectra of Pac , Pad , and Pae showed no signals corresponding to the 1,1-vinylidene units (Figures S18, S22, and S26).…”

“…To assess the reactivity of 1a , a small molecular model reaction with 4-ethynyltoluene ( 2a ) was conducted, as described in our previous report . The hydroarylation reaction of 1a with 2a proceeded quantitatively in the presence of [Cp*Co­(CH 3 CN) 3 ]­(SbF 6 ) 2 (2 mol %) and neodecanoic acid (NDA, 30 mol %) in 1,2-dichloroethane (DCE, 0.05 M) at 30 °C for 1 h. A hydroarylation reaction occurred selectively at the 5,5′-positions of 1a and gave the dialkenylated product ( 3aa) in a good yield (Scheme and Figure S1).…”

“…The other regents were also purchased from Kanto Chemical, Tokyo Chemical Industry, and Sigma Aldrich. N , N , N′ , N′ -Tetrahexyl-(2,2′-bithiophene)-4,4′-dicarboxamide ( 1a ), N , N , N′ , N′ -tetracyclohexyl-(2,2′-bithiophene)-4,4′-dicarboxamide ( 1d ), 6,6′-diethynyl-1,1′-bis­(2-ethylhexyl)­isoindigo ( 4e ), and 1,4-diethynyl-2,3,5,6-tetrafluorobenzene ( 4f ) were prepared referring to procedures reported in the literature. ,, 2,7-Diethynyl-9,9-bis­(2-ethylhexyl)­fluorene ( 4b ), 2,7-bis­(4-ethynylphenyl)-9,9-di­( n -octyl)­fluorene ( 4a ), and [Cp*Co­(CH 3 CN) 3 ]­(SbF 6 ) 2 were synthesized by the same methods as our previous reports. , The synthesis of 2,6-bis­(4-ethynylphenyl)-4,4-bis­(2-ethylhexyl)­cyclopenta­[2,1- b :3,4- b ′]­dithiophene ( 4d ) is described in the Supporting Information. Poly­(3,4-ethylenedioxythiophene)-poly­(styrenesulfonate) (PEDOT:PSS, CLEVIOS P VP AI 4083) was purchased from Heraeus.…”

“…Poly­(arylenevinylene)­s (PAVs) were the first polymer materials used for OLEDs. − To synthesize PAVs, polyaddition via the hydroarylation of alkynes is an ideal method because the production of byproducts from monomers can be eliminated. However, examples of hydroarylation polyadditions are limited. , We recently reported the Cp*Co­(III)-catalyzed hydroarylation polyaddition of aromatic diynes with pyrrole derivatives as a new synthetic method for preparing PAVs (Figure a) . Furthermore, we discovered the occurrence of intramolecular catalyst transfer through the directing group, which allowed us to control both terminals of the PAVs to alkyne moieties via nonstoichiometric polyaddition .…”

“…Moreover, the 1,1-vinylidene unit was produced from a side reaction at the migratory insertion of alkynes into the Co catalyst, lowering the regioselectivity of the PAVs to 80–93%. It is ideal to synthesize PAVs with high regioselectivity because the 1,1-vinylidene unit serves as a defect that decreases the carrier mobility in electronic devices …”