Kumada Catalyst-Transfer Polycondensation of Thiophene-Based Oligomers: Robustness of a Chain-Growth Mechanism

Abstract

Synthesis.2-Bromo-3-hexyl-5-iodothiophene (6). NBS (37.38g, 0.21 mol) was added to the solution of 3hexylthiophene (33.66 g, 0.2 mol) in 500 mL of a chloroform-acetic acid mixture (50/50 v/v) in the absence of light, under an argon atmosphere, at temperature 0°C. The mixture was allowed to reach room temperature, and stirred overnight, and hydrolyzed with 500 mL of ice-water, and the aqueous phase extracted with chloroform. The combined extracts were washed with water, 1 M sodium hydroxide solution (50 ml), again with water, dried (MgSO4), and concentrated. The residue was purified by flash chromatography to give 44.45 g (0.18 mol) of monobromide 4 (90% yield). Iodination was performed in a similar manner. To this end, NIS (21.26 g, 95 mmol) was added to 4 (22.25 g, 90 mmol) in 500 mL of a chloroform-acetic acid mixture (50/50 v/v) in the absence of light, under an argon atmosphere, at temperature 0°C. The mixture was allowed to reach room temperature, stirred overnight,

Kumada Catalyst‐Transfer Polycondensation: Mechanism, Opportunities, and Challenges

“…Thus, KCTP not only follows the chain-growth mechanism but even displays the characteristics of a ''living'' polymerization process. [62] While we and several other research groups have confirmed the chain-growth mechanism for the KCTP of 1 [22,24,63,64] and other monomers, [28][29][30][31][65][66][67] Achord and Rawlins [68] reported data that contradict the observations of the livingness of KCTP. [24,69] General Mechanism…”

“…The first ex situ prepared Ni initiators were synthesized by Senkovskyy et al starting from Ni(PPh 3 ) 4 , which undergoes oxidative addition with various arylhalides such as bromobenzene or orthobromotoluene, to give the desired adducts Ar-Ni(PPh 3 ) 2 -Br (Scheme 3a). [44,65] It was found that KCTP of 1 initiated by these complexes proceeds via chain-growth and led to regioregular P3HT with a relatively broad polydispersity of %1.6. Almost 100% of the initiator Ar-group was incorporated into the polymer for DPs smaller than 30, as evidenced by 1 H NMR and MALDI-ToF analysis.…”

“…Above DP ¼ 30, reinitiation occurred resulting in a significant fraction of P3HT that did not contain the initiator group. [65] Doubina et al [70] used the air-stable 3 have shown a much worse performance than bidentate ligands such as dppp or dppe, which was ascribed to extensive chaintermination and reinitiation reactions. [43,44] An one-pot preparation of Ni-initiators supported by bidentate ligands was attempted by Doubina et al Nickel cyclooctadiene (Ni(cod) 2 ) was reacted with aryl halides followed by the addition of one equivalent of a bidentate ligand (dppf, dppe, or dppp), or of two equivalents of the monodentate ligand PPh 3 (Scheme 3c).…”

“…However, an appreciable degree of Ar group incorporation into the polymer was achieved only for PPh 3 , while the use of the bidentate ligand dppp resulted in the KCTP-inert complex Ni(dppp) 2 . The same group tried to activate aryl chlorides with Ni(PPh 3 ) 4 , similar to Beryozkina et al, [65] followed by ligand exchange with the bidentate ligand dppp. [72] Nickel complexes with phenyl-and ortho-tolyl chloride were successfully synthesized and allowed for the preparation of the corresponding Ar-terminated P3HT with controlled MW and almost complete transfer of the initiator group (Scheme 3d).…”

The Controlled Polymerization of Poly(cyclopentadithiophene)s and Their All-Conjugated Block Copolymers

“…Indeed, it has been shown by KCTPpolymerization of bi-and terthiophene, that the chain-growth polymerization is maintained for longer monomer units, however with higher chain-transfer probabilities and, resultantly, a decreased controlled character. 73 In the case of CPDT, however, our experiments indicate that transfer and termination reactions occur only limited during the polymerization. Furthermore, after a full conversion of the first CPDT-equivalent (after 20 min), all growing polymer chains remain active and continue to grow after a second equivalent is added.…”