Synthesis of High-molecular-weight Head-to-tail-type Poly(3-substituted-thiophene)s by Cross-coupling Polycondensation with [CpNiCl(NHC)] as a Catalyst

Abstract

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...

Dehalogenative or Deprotonative? The Preparation Pathway to the Organometallic Monomer for Transition‐Metal‐Catalyzed Catalyst‐Transfer‐Type Polymerization of Thiophene Derivatives

“…When a nickel(II) catalyst with NHC and cyclopentadienyl (Cp) ligands 21 is employed for the polythiophene synthesis, polythiophene of extremely high‐molecular‐weight was revealed to be obtained . The nickel complex 21 is easily prepared by the reaction of nickelocene (Cp 2 Ni) with several HCl salts of NHCs and the polymerization of bromothiophene 4 with 0.75 mol % CpNiCl(SIPr) ( 21 ) and Knochel–Hauser base 19 afforded regioregular HT‐polythiophene 1 of molecular weight of ca.…”

Nickel N-heterocyclic carbene complexes and their utility in homogeneous catalysis

“…The complexes (175) [311] and (278) [312] catalyzed the polycondensation of thiophene derivatives to obtain regiocontrolled high molecular weight polymers.…”

Recent developments in the synthesis of regioregular thiophene-based conjugated polymers for electronic and optoelectronic applications using nickel and palladium-based catalytic systems

“…170,[172][173][174] Employment of 2-halo-3-substituted thiophenes instead of 2,5-dihalothiophenes along with the Knochel-Hauser 167,175 base have been the key for the successful synthesis of thiophenebased polymers. 170,[176][177][178][179][180][181][182] Magnesium amide does not interfere with the propagation of the polymer during the course of the reaction. 164 Dehydrobrominative polycondensation proceeds with the higher atom efficiency compared to the dehalogenative polycondensation employing Grignard reagent.…”

“…In 2013, Shunsuke Tamba and co-workers reported the use of [CpNiCl(SIPr)] catalyst for the synthesis of extremely high molecular weight head-to-tail type regioregular poly(3-alkylthiophene) via dehydrobrominative polycondensation. 179 Polymerization of 2-bromo-3-hexylthiophene proceeded with a catalytic amount of [CpNiCl(SIPr)] and an equivalent amount of Knochal-Hauser base to yield regioregular poly(3hexylthiophene) 16 up to M w ¼ 815 000. A self-standing lm of polythiophene was obtained with M w ¼ 414 000, while the attempted formation of corresponding lms with lower molecular weight (M w ¼ 38 000) was not successful.…”