Journal of Polymer Science Part A: Polymer Chemistry, Vol.54, No.15, 2346-2351, 2016
Novel Isolated, L-Amino Acid-Ligated Rhodium Catalysts that Induce Highly Helix-Sense-Selective Polymerization of an Achiral 3,4,5-Trisubstituted Phenylacetylene
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-senseselective 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 (M-w 28 x 10(4)-45 x 10(4)) 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 [theta](310) = 13.0 x 10(4) deg cm(2)/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. (C) 2016 Wiley Periodicals, Inc.
Keywords:catalysis;chiral;helix-sense-selective polymerization;L-amino acid;NMR;3,4,5-trisubstituted phenylacetylene