Influence of the Boron Moiety and Water on Suzuki–Miyaura Catalyst‐Transfer Condensation Polymerization

Abstract

Although water promotes Suzuki-Miyaura coupling reaction, it also induces side reactions such as deboronation and dehalogenation. Therefore, Suzuki-Miyaura polymerization of triolborate halothiophene monomer 1 with (t) Bu3 PPd(o-tolyl)Br (2) in dry tetrahydrofuran (THF) is investigated. However, the resultant poly(3-hexylthiophene) (P3HT) shows a broad molecular weight distribution and uncontrolled polymer ends. Model reactions of a number of boron reagents 3 with 2,5-dibromothiophene (4) in the presence or absence of water indicate that intramolecular transfer of the catalyst is hardly affected by the boron moiety of 3, whereas it is hindered in the absence of water. Indeed, polymerization of 1 with 2 in H2 O/THF affords P3HT with a narrower molecular weight distribution and controlled tolyl/H ends, as compared to the reaction in dry THF.

Advances in the controlled polymerization of conjugated polymers

“…The main drawback of this method is the high toxicity of the organotin compounds necessary during the synthesis of the monomers, but a lot of functional groups can be incorporated into the monomer and no optimization of the base, organoboron moiety or the amount of water is required. 65 As well for PPE 9 as for P3AT 10 controlled chaingrowth polymerizations were obtained via Stille catalyst transfer polymerization.…”

“…were designed and used in purified form for the synthesis of poly(fluorene) (PF) 8,57-63 , P3AT 58,[64][65][66] , PPP 57,62,66 , poly(3,6-phenanthrene) (PPhen) 67 , n-type fluorene copolymers 68 and poly(pyridine-3,6-diyl) (PPyr) 69 . However, the synthesis of the last polymer was not controlled due to the presence of disproportionation reactions.…”

“…Mostly Pdcatalysts are used in SCTP and small amounts of water are added to favor the intramolecular transfer of this catalyst. 65 Yokoyama et al were the first to use Suzuki-Miyaura couplings to obtain a chain-growth polymerization. PF with a low dispersity was obtained when (Ph)Pd(P t Bu3)Br was used as catalyst.…”

“…8 Later on, also other catalytic systems were found to be successful for SCTP of PFs. 61,62,140,141 Besides PFs also PPP 57 and P3AT 65,141,142 were synthesized in a controlled way with SCTP using Pd-catalysts. Recently, a controlled Nicatalyzed SCTP of poly(thiophene)s was performed.…”

Pairing Suzuki–Miyaura cross-coupling and catalyst transfer polymerization

“…Phase-transfer agents such as 18-crown-6 have also been used in polymerization to aid in extraction of the base into the organic phase. 47,50,59 The amount of base used in polymerizations can span a wide range (1-20 equiv. ), which can impact initiation and polymerization rates.…”