Helix-Sense Selective Polymerization of Carbodiimides: Building Permanently Optically Active Polymers from Achiral Monomers

作者：Gonglu Tian, Yujie Lu, Bruce M. Novak · 发表于：Journal of the American Chemical Society · 年份：2004 · DOI：10.1021/ja049548m · 被引用次数：99 · 研究领域：Synthesis and Properties of Aromatic Compounds、Supramolecular Chemistry and Complexes、Axial and Atropisomeric Chirality Synthesis

The helix-sense selective polymerization of achiral monomers by homochiral catalysts was investigated. Polymerization of chiral carbodiimides (N-(R)-2,6-(dimethylheptyl)-N'-phenylcarbodiimide) by achiral catalysts yields polymers that undergo mutorotation at elevated temperatures, thus illustrating that these chains are formed under kinetic rather than thermodynamic control. Building on this observation, the polymerization of achiral carbodiimides by (S-BINOL)Ti(OiPr)2, I, was studied. Monomers (N-hexyl-N'-(X)carbodiimide, where X = isopropyl (3), hexyl (4) or phenyl (5)), N-methyl-N'-(2-methyl-6-isopropylphenyl)carbodiimide, 6, and N-dodecyl-N'-(1-naphthyl)carbodiimide, 7, were all polymerized with I in good yields (86-95%), and all showed varying degrees of asymmetric induction. Poly-3, -4, and -5 racemized upon heating at elevated temperatures, but poly-6 and poly-7, bearing nonsymmetric phenyl groups, yielded optically active polymers that could not be racemized even at elevated temperatures. Thin films of poly-7 were found to be highly opalescent.