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

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 p-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.