Chemoselective Cross-Coupling Reactions as Tools in Synthesis and Applications for Polymer Chemistry
A nucleophile-selective cross-coupling reaction with vinyl and alkynyl bromides on a dinucleophilic thiophene bearing two metal groups, a boronic ester and a stannyl group, has been developed. The first nucleophilic site to react is the stannyl group, and subsequently, a Suzuki–Miyaura cross-coupling takes place after adding a second electrophile, base and water. The generality of the reaction was shown with various electron rich, electron neutral, electron poor vinyl bromides and alkynyl bromides. The roles typical in Sonogashira couplings or Heck reactions of the aromatic ring as the dielectrophile coupling to vinyl and alkynyl metal species are reversed, which presents a new tool for organic synthesis. Four different difunctional thienylpyrrole monomers with a bromide group on the thienyl moiety and a metal group (Mg, B, Sn or Zn) on the pyrrole moiety were developed. Based on those monomers, π-conjugated poly(thiophene-alt-pyrrole)s PTPs were firstly synthesized via nickel and palladium catalyzed Kumada polycondensation from this A-B type monomer. The polymers were analyzed by NMR, IR, GPC, MALDI-MS, UV-vis, PL and TGA measurements.