A Step-Efficient Pathway to Chlorine-Functionalized Thiophene Oligomers by Palladium-Catalyzed Deprotonative Coupling of Chlorothiophenes

Abstract

Deprotonative metalation of 2-chloro-3-substituted thiophene at the 5-position of the thiophene ring is performed by a bulky magnesium amide 2,2,6,6-tetramethylpiperidin-1-yl magnesium chloride lithium chloride salt (TMPMgCl•LiCl). The obtained metallic species reacts with bromothiophene to afford the regioregular head-to-tail-type chlorobithiophene, which is subjected to further end functionalization by the coupling reaction with C-Cl bond. Deprotonative C-H coupling polycondensation of differently-substituted chlorobithiophene gives polythiophene of the formal alternating copolymer.

Formal preparation of regioregular and alternating thiophene–thiophene copolymers bearing different substituents

“…The synthesis of chlorobithiophenes with different substituents at the 3-and 3'-position was carried out in a manner that we have described previously [25]. We chose five chlorobithiophenes as monomer precursors for the alternating copolymers, as summarized in Scheme 3.…”

“…NiCl 2 (PPh 3 )IPr (5) was purchased from TCI Co. Ltd. All other chemicals were purchased and used without further purification. The preparation of the chlorobithiophenes 4a and 4b was performed in a manner reported previously [25].…”

“…The synthesis of the chlorobithiophenes 4 was carried out in a manner shown in our previous report [25]. The spectroscopic properties and analytical data for 4 are summarized below.…”

“…We further focused on the copolymerization of thiophene, employing differently substituted thiophene monomers, with which several copolymerizations are plausible, giving thiophene-thiophene copolymers of random (statistical) [15], gradient [16,17], block [18,19], alternating [20][21][22][23], etc. [24,25] makeup. We are thus interested in the preparation of alternating polythiophenes bearing two kinds of different substituents.…”

“…We have recently shown that the coupling of 2-chloro-3-substituted thiophene 2 with 2-bromo-3-substituted thiophene 3 efficiently gave chlorobithiophene 4 in a facile manner (Scheme 2) [25]. The use of a palladium catalyst efficiently suppressed the undesired polymerization to afford the HT halobithiophene with different substituents [26].…”