Application of "transfer-free" Suzuki coupling protocols toward the synthesis of "unambiguously linear" poly(p-phenylenes)

Soluble derivatives of poly(p-phenylene) of high molecular weight were synthesized via Suzuki coupling reactions catalyzed by palladium(0) precursors in the presence of either triphenylphosphine (TPP) or tri(o-tolyl)phosphine (TOTP). Syntheses involving the former ligand resulted in the formation of polymers in which the incorporation of phosphine was clearly observable by P-31 NMR. However, polymers formed utilizing the latter ligand in a hydrophobic solvent such as CH2Cl2 exhibited no signals in the P-31 NMR spectrum, even after 20 000 scans. Analyses by tandem GPC-light scattering and tandem GPC-light scattering-viscometry showed that polymers synthesized by utilizing a large amount of TPP-based catalyst (2%) possessed a considerably lower molecular weight than did the other samples and exhibited markedly different dependencies of the radius of gyration and intrinsic viscosity on molecular weight. From these studies, it does appear that the aryl-aryl interchange reaction known to occur in ArPdL2I complexes significantly affects the architecture of these polymers.