Due to a wide range of applications in electronic materials, polythiophenes attract considerable attention in organic and polymer syntheses as well as in materials science. For the purpose of developing the practical synthetic protocol, this review focuses on the deprotonative pathway in the preparation of thiophene organometallic monomer, which was shown to be effective employing 2‐halo‐3‐substituted thiophene as a monomer precursor. The thus metallated thiophene monomer was shown to undergo polymerization by nickel(II) complex catalysis, with which highly regioregular head‐to‐tail (HT)‐type polythiophenes were obtained with controlled molecular weight and molecular weight distribution. Several polythiophene derivatives with modified thiophene‐ring and side‐chain structures were shown to be designed in order to achieve the designed functionality as materials.

The unprecedented synthesis of regioregular headto-tail-type poly(1,4-arylene)s bearing different substituents at the 2-and 5-positions is described. They were prepared by the polymerization of 2,5-disubstituted bromo(chloro)arylenes by selective halogen-metal exchange with aGrignardreagent and subsequent cross-coupling polymerization with an ickel catalyst [NiCl 2 (dppp)].F ormation of the regioregular poly(1,4arylene)s were confirmed by NMR spectroscopy, and showed remarkable differences to those polymers having uncontrolled regioregularity.Polymerization of bromo(chloro)arylenes with achiral alkoxy substituent also led to the regioregular head-totail-type polyarylene,w hichd emonstrated circular dichroism, thus suggesting formation of as tructure with higher-order regularity.Scheme 1. Polymerization of the 1,4-dibromoarylene 3a.

Chiraphos (2,3-diphenylphosphinobutane) serves as a 1 highly effective ligand for nickel catalyst in the cross-2 coupling polymerization reaction. Nickel(II) catalyst 3 efficiently promotes the cross-coupling polymerization of 4 2,5-differently substituted 1,4-dihalobenzene particularly 5 bearing a sterically congested substituent at the side chain 6 affording the corresponding poly(1,4-phenylene). Such a 7 highly active catalyst allowed the polymerization with 8 diverse degree of polymerization with controlled molecular 9 weight. 10

The unprecedented synthesis of regioregular head‐to‐tail‐type poly(1,4‐arylene)s bearing different substituents at the 2‐ and 5‐positions is described. They were prepared by the polymerization of 2,5‐disubstituted bromo(chloro)arylenes by selective halogen–metal exchange with a Grignard reagent and subsequent cross‐coupling polymerization with a nickel catalyst [NiCl2(dppp)]. Formation of the regioregular poly(1,4‐arylene)s were confirmed by NMR spectroscopy, and showed remarkable differences to those polymers having uncontrolled regioregularity. Polymerization of bromo(chloro)arylenes with a chiral alkoxy substituent also led to the regioregular head‐to‐tail‐type polyarylene, which demonstrated circular dichroism, thus suggesting formation of a structure with higher‐order regularity.

Themis, the Goddess of Justice in the Greek mythology, judges with blindfolded eyes the case thiophene for the catalyst‐transfer‐type polymerization. The balance scale in her left hand shows the imbalance between dibromothiophene and chlorothiophene, suggesting that smaller weight loss from chlorothiophene leads to the regioregular poly(3‐substituted thiophene) in a more atom‐efficient manner. For more details see the Minireview by A. Mori and Y. Shibuya on page 6976 ff.