Palladium-catalyzed selective dehalogenative homocoupling polymerization of AB2-type dihaloaryl sulfonate monomers

In a preliminary set of model reactions, the palladium-catalyzed dehalogenative homocoupling of AB-type haloaryl sulfonates such as haloaryl mesylates and haloaryl tosylates under reductive conditions has proceeded selectively depending on the type of the halogen. Thus, in the presence of PdCl2(PPh3)2 and zinc, a bromo or an iodo leaving group of haloaryl sulfonates was homocoupled to give symmetrical biaryls in good yields with the sulfonate leaving group intact indicating that the relative reactivities of the two leaving groups are sufficiently distinct to give chemoselectivity, whereas a chloro leaving group gave no reaction under the conditions used. When the more reactive nickel catalyst was employed instead of the palladium catalyst in the reaction, both dehalogenative and desulfonative homocouplings of haloaryl sulfonates occurred regardless of the type of the halogen used. Similarly, AB2-type dihaloaryl sulfonate monomers (i.e. 2,4-dibromophenyl mesylate and 2,4-dibromophenyl tosylate) were shown to undergo palladium-catalyzed selective dehalogenative homocoupling polymerization to produce poly(phenylene)s (PPs) with mesylate or tosylate leaving groups in their backbone. These sulfonate-substituted PPs were transformed into the crosslinked and water-soluble PPs, respectively, via subsequent chemical modifications.