Copper(I)-Catalyzed Asymmetric Oxidative Coupling Polymerization of 2,3-Dihydroxynaphthalene Using Bisoxazoline Ligands

Abstract

The asymmetric oxidative coupling polymerization of 2,3-dihydroxynaphthalene with the complexes of Cu(I)−bisoxazoline as a catalyst under an O2 atmosphere was successfully accomplished to produce poly(2,3-dihydroxy-1,4-naphthylene) having a continuous 1,1‘-bi-2-naphthol main chain structure. For example, the polymerization with (S)-2,2‘-isopropylidenebis(4-phenyl-2-oxazoline) as a ligand at room temperature for 24 h afforded a methanol-insoluble polymer in 30% yield with a molecular weight of approximately 4.1 × 103 as estimated by 13C NMR analysis, and the polymer was quantitatively obtained after 48 h. The obtained polymer was rich in the S-configuration. The structure of the bisoxazoline ligands significantly affected the catalyst activity and stereoselectivity.