Novel isolated, L-amino acid-ligated rhodium catalysts that induce highly helix-sense-selective polymerization of an achiral 3,4,5-trisubstituted phenylacetylene

Abstract

Two novel chiral well-defined rhodium complexes, Rh(cod)(L-Phe) (cod = 1,5-cyclooctadiene, Phe = phenylalanine) and Rh(cod)(L-Val) (Val = valine) were synthesized, isolated by recrystallization, and characterized. The helix-sense-selective polymerization (HSSP) of an achiral 3,4,5-trisubstituted phenylacetylene, p-dodecyloxy-m,m-dihydroxyphenylacetylene (DoDHPA) was examined by using the two Rh complexes as catalysts. These catalysts provided high molecular weight polymers (Mw 28 × 104−45 × 104) in about 40%–85% yields. The resulting polymers exhibited a bisignated CD signal at about 300 nm and a broad signal around 470 nm, indicating that they have preferential one-handed helical structure. The present catalysts achieved larger molar ellipticity up to [θ]310 = 13.0 × 104 deg cm2/dmol than those with binary chiral catalytic systems, [Rh(cod)Cl]2/(L-phenylalaninol), [Rh(cod)Cl]2/(L-valinol), and [Rh(nbd)Cl]2/(R)-PEA. All these results manifest that the present, well-defined Rh complexes serve as excellent catalysts for the HSSP of DoDHPA. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2346–2351