Asymmetric oxidative coupling polymerization of dihydroxynaphthalene derivatives with cobalt-salen complexes

Abstract

The oxidative coupling polymerization of dihydroxynaphthalene derivatives with a novel catalyst system, the cobalt(II)-salen complexes, was investigated. For example, the asymmetric polymerization of 2,3-dihydroxynaphthalene with (R,R)-(–)-N,N’-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II) in a dichloromethane-methanol mixed solvent at room temperature for 0.5 h under an oxygen atmosphere, followed by acetylation of the hydroxyl groups, produced a methanol-insoluble polymer with the specific rotation value [α]D of +165, which was rich in the R-configuration. To estimate the enantioselectivity during the polymerization, the corresponding acetylated dimer product was isolated from a polymerization mixture and determined to be 58% e.e.