Revisiting Murahashi coupling, we found that it effectively allows polymerization of lithiated (hetero)arenes by nickel(II)-catalyzed polycondensation. Deprotonative polymerization of 2-chloro-3-substituted thiophene with n-butyllithium gave head-to-tail-type poly(3-substituted thiophene). Poly(1,4-arylene)s were obtained by the reaction of the corresponding dibromides through lithium-bromine exchange. A lithiated thiophene derivative obtained via deprotonative halogen dance also underwent polymerization to afford a bromo-substituted polythiophene.

High-molecular-weight head-to-tail-type regioregular polythiophenes are synthesized by [CpNiCl(SIPr)]-catalyzed dehydrobrominative polycondensation. Polycondensation of 2-bromo-3-hexylthiophene at the CH bond proceeds with an equimolar amount of TMPMgCl¢LiCl and a catalytic amount of [CpNiCl(SIPr)] to afford the regioregular poly(3-hexylthiophene) (HT-P3HT) with up to M w = 815000. A self-standing HT-P3HT film is obtained with the regioregular HT-P3HT of M w = 414000, while the attempted formation of the corresponding film with lower-molecular-weight HT-P3HT (M w = 38000) is unsuccessful.Polythiophenes have attracted considerable attention recently because of their remarkable physical properties as electronic materials.1 The formation of head-to-tail (HT)-type polythiophenes such as poly(3-hexylthiophene) (P3HT) (1) has been particularly important, since superior material performances have been generally found in HT-P3HT materials because of their highly planer and ³-conjugation-extended characteristics. 2In contrast with the extensive spectroscopic and electronic characterizations of HT-type polythiophenes, the mechanical performance of HT-polythiophene as a self-standing film has rarely been studied owing to the preparative difficulties involved in the synthesis of high-molecular-weight HT-P3HT.3 Although regioregular HT-P3HT was shown to be prepared by nickelcatalyzed polycondensation of the corresponding dibromothiophene with a Grignard reagent (the GRIM method), 4 it had been difficult to obtain HT-P3HT with a molecular weight as high as 100000.5 Very recently, Seferos and co-workers revealed that the synthesis of higher-molecular-weight P3HT could be achieved with [(o-tolyl)NiCl(dppp)] as an initiator, affording polythiophene with a molecular weight up to ca. 200000. 6 This prompted us to report our separate findings on the development of a new class of nickel catalysts bearing a cyclopentadienyl (Cp) ligand for the polymerization of thiophene derivatives to yield highmolecular-weight HT-P3HT. We have reported recently that nickel-catalyzed dehydrobrominative or dehydrochlorinative polycondensation is also a powerful tool (in addition to the GRIM method) for the synthesis of HT-type polythiophenes using the KnochelHauser base, chloromagnesium 2,2,6,6-tetramethylpiperidide lithium chloride salt (TMPMgCl¢LiCl), 7 in the presence of a nickel(II) catalyst. 8 The method allows polymerization at a lower reaction temperature within a shorter polymerization period with high atom efficiency. In our studies on the dehydrobrominative synthesis as well as the aforementioned GRIM method, 9,10 it is remarkable that the average molecular weight of HT-P3HT is controllable by the ratio of monomer feed and catalyst loading, because of the characteristics of living polymerization. In the course of our studies on the synthesis of HT-P3HT, we found unexpectedly that P3HT of an extremely high molecular weight (>100000) was obtained irrespective of the catalyst loading when a nickel catalyst bearing a cyclopentadienyl (Cp) a...

Cross-coupling polycondensation of thiophene derivatives occurs via C–S bond cleavage in the presence of a nickel catalyst. Head to tail type (HT) regioregular poly(3-hexylthiophene) is obtained by a nickel(II)-catalyzed deprotonative C–H functionalization polycondensation of 2-(phenylsulfonyl)-3-hexylthiophene with stoichiometric TMPMgCl·LiCl or with the catalytic secondary amine/RMgX. Debrominative Grignard metathesis (GRIM) polymerization with 5-bromo-2-(phenylsulfonyl)-3-hexylthiophene also proceeds by the catalysis of the nickel(II) complex to afford the corresponding polythiophene.