Alternating Intramolecular and Intermolecular Catalyst‐Transfer Suzuki–Miyaura Condensation Polymerization: Synthesis of Boronate‐Terminated π‐Conjugated Polymers Using Excess Dibromo Monomers

Abstract

The Suzuki-Miyaura coupling polymerization of dibromoarene 1 and arylenediboronic acid (ester) 2 with a Pd catalyst having a high propensity for intramolecular catalyst transfer is reported. The polymerization of excess 1 with 2 affords high-molecular-weight π-conjugated polymer having boronic acid (ester) moieties at both ends, contrary to Flory's principle. This unstoichiometric polycondensation behavior is accounted for by intramolecular transfer of the Pd catalyst on 1. In the polymerization of 1 and 2 having different aryl residues, high-molecular-weight polymer is obtained when the stronger donor aromatic is used as the dibromo monomer and the weaker donor or acceptor aromatic is used as diboronic acid (ester) monomer. The pinacol boronate moieties at both ends of the obtained poly(p-phenylene) (PPP) can be converted to benzoic acid ester, hydroxyl group, and bromine. Furthermore, the reaction of the pinacol boronate-terminated PPP with poly(3-hexylthiophene) (P3HT) having bromine at one end yields a triblock copolymer of P3HT-b-PPP-b-P3HT.

Intramolecular Catalyst Transfer on a Variety of Functional Groups between Benzene Rings in a Suzuki–Miyaura Coupling Reaction

“…Since we found that t Bu 3 PPd undergoes intramolecular transfer on several functional groups, we applied this chemistry to Suzuki–Miyaura unstoichiometric polycondensation of 1.3 equivalent of 1 and 1.0 equivalent of phenylenedibronic acid 5 in the presence of t Bu 3 PPd G2 precatalyst (Scheme , Table ). Intramolecular catalyst transfer on 1 is expected to afford high‐molecular‐weight polymer with boronic acid moieties at both ends even if excess 1 is used, as in the case of unstoichiometric Suzuki–Miyaura polycondensation of aromatic monomers . Indeed, polycondensation using 1 a – d , and 1 g , which exhibited intramolecular catalyst transfer in the reaction with 2 (Table ), afforded high‐molecular‐weight polymer ( M n ≥7500) (Table , entries 1–4, and 7), and the polymer obtained in the initial stage appeared to have boronic acid moieties at both ends (Figures S12, S14, S17, and S20, Supporting Information), although the polymer formed from 1 g and 5 did not show any peaks in the MALDI‐TOF mass spectrum.…”

Intramolecular Transfer of Pd Catalyst on Carbon–Carbon Triple Bond and Nitrogen–Nitrogen Double Bond in Suzuki–Miyaura Coupling Reaction

“…Dry tetrahydrofuran (THF, stabilizer-free, Kanto, Tokyo, Japan) and distilled water (Wako, Tokyo, Japan) were used as received. Dibromoazobenzene 1b [18] and phenylenediboronic acid 6a [11] were prepared according to the literature.…”

“…When this t-Bu 3 PPd(0) catalyst, which has a propensity for intramolecular catalyst transfer on a π-electron face, was used for Suzuki-Miyaura coupling polymerization of dibromoarene and arenyldiboronic acid ester (AA + BB polycondensation), high-molecular-weight π-conjugated polymer with a boronate moiety at both ends was obtained, even though excess dibromoarene was used [11]. This unstochiometric polycondensation behavior is accounted for by successive substitution of the bromides in dibromoarene with arenyldiboronic acid ester or oligomers having boronate moieties at Catalysts 2017, 7,195; doi:10.3390/catal7070195 www.mdpi.com/journal/catalysts both ends through intramolecular transfer of the Pd catalyst on the π face of dibromoarene.…”

Mechanistic Investigation of Catalyst‐Transfer Suzuki–Miyaura Condensation Polymerization of Thiophene–Pyridine Biaryl Monomers with the Aid of Model Reactions

“…Kramer and co‐workers synthesized regio‐regular/irregular cyclopentadithiophene–pyridylthiadiazole alternating copolymers, and found that the hole transport property ( μ e ) of the regio‐regular alternating copolymer was approximately 100 times better than that of the regio‐irregular copolymer . Moreover, we have recently found that Suzuki–Miyaura coupling polymerizations of diboronic acid ester and dibromoarene in the presence of t Bu 3 PPd precatalyst affords high‐molecular‐weight boronate‐terminated π‐conjugated polymers, even if excess dibromoarene is used, and we synthesized a fluorene–benzothiadiazole ( D –A) alternating copolymer with terminal boronate groups by using this method . Higashihara and co‐workers reported similar Stille coupling copolymerizations of distanylthiophene (D) and excess dibromonaphthalenediimide (A), but did not mention the polymer end groups …”

“…[7] Moreover,w eh ave recently found that Suzuki-Miyaura coupling polymerizations of diboronic acid ester and dibromoarene in the presence of tBu 3 PPd precatalyst [8] affords high-molecular-weight boronate-terminated p-conjugated polymers, even if excess dibromoarene is used, and we synthesized af luorene-benzothiadiazole (D-A) alternating copolymer with terminal boronate groups by using this method. [9] Higashihara and co-workers reporteds imilar Stille coupling copolymerizationso fd istanylthiophene (D) and excess dibromonaphthalenediimide (A), but did not mention the polymer end groups. [10] Regarding the control of molecular weight and dispersity of D-A p-conjugated alternating copolymers, catalyst-transfer condensation polymerization (CTCP), which proceeds in ac hain-growthp olymerization manner,o fm onoaromatic AB monomers through Kumada-Tamao, [11] Suzuki-Miyaura, [12] Negishi, [13] Murahashi, [14] or Stille [15] couplingr eactions has been extendedt oC TCP of D-A biaryl and D-A-D teraryl monomers to afford D-A p-conjugated alternating copolymers with defined molecular weightand low dispersity.Kiriy and co-workers first demonstrated that thiophene-thiophene( D-D) biaryl monomers underwent Ni-catalyzed Kumada-Tamao CTCP.…”