An optically inactive polyacetylene, poly((4-carboxyphenyl)acetylene) (poly-1), exhibits an induced circular dichroism (ICD) in the UV-visible region upon complexation with chiral amines and amino alcohols in DMSO and in the film, the sign of which reflects the stereochemistry including bulkiness, type (primary, secondary, or tertiary), and absolute configuration of the amines. Therefore, the polyacetylene can be used as a novel probe for determining the chirality of amines. Most primary amines and amino alcohols of the same configuration gave the same sign for the induced Cotton effect; however, secondary and/or tertiary amines used in the present study tended to show Cotton effect signs opposite to those of the primary amines and amino alcohols of the same configuration. The magnitude of the ICD likely increases with an increase in the bulkiness of the chiral amines. The complexation dynamics during the formation of the helical structure of poly-1 with chiral amines were investigated on the basis of the spin-spin relaxation behavior and 1 H NMR, CD, and optical rotatory dispersion (ORD) titrations. The complex formation of poly-1 with chiral amines such as 1-(1-naphthyl)ethylamine and 2-amino-1-propanol exhibits a positive nonlinear effect between the enantiomeric excess of the chiral amines and amino alcohols and the observed ellipticity of the Cotton effects. The excess enantiomer bound to poly-1 may induce an excess of a single-handed helix (rightor left-handed helix), which may result in a more intense ICD than that expected from the ee of the amine. Moreover, it was found that the coexistence of achiral amines such as 1-aminoethanol also induced an excess of one helical sense of poly-1.

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Five phenylacetylenes bearing an amino group such as 4‐amino (1), 3‐amino (2), 4‐N,N‐dimethylamino (3), 4‐aminomethyl (4), and 4‐N,N‐diisopropylamino‐methyl (5) group on the phenyl group, 4‐pyridylacetylene (6), and 2‐pyridylacetylene (7) were synthesized and polymerized with [Rh(nbd)Cl]2 (nbd: norbornadiene). Monomer 5 showed the highest polymerizability and afforded quantitatively a fibrous polymer, whereas the other monomers showed lower reactivity and the resulting polymers were powdery. Although most polymers were not soluble in common organic solvents such as tetrahydrofuran (THF), chloroform, acetonitrile, and dimethyl sulfoxide, some polymers were soluble in the presence of carboxylic acids. Among the polyphenylacetylene derivatives, only poly‐5 having a stable, highly cis‐transoidal stereoregular structure exhibited an induced circular dichroism (ICD) in the UV‐visible region, probably due to a prevailing one‐handed helical conformation upon complexation with optically active carboxylic and α‐hydroxy acids such as mandelic acid, lactic acid, and 2‐phenylbutyric acid in THF, the sign of which reflected the absolute configuration of the acids. Therefore, poly‐5 can be used as a novel probe for determining the chirality of acids. The α‐hydroxy acids of the same configuration gave the same sign in induced Cotton effect in THF. However, carboxylic acids used in the present study showed the opposite signs to those of the α‐hydroxy acids when their absolute configurations were same. The magnitude of the ICDs seems to depend on the bulkiness of the α‐hydroxy acids. On the contrary, other poly(phenylacetylenes) bearing an amino group and poly(pyridylacetylenes) did not show any ICD in the presence of optically active acids, probably because of either low basicity for the acid‐base complexation or low stereoregularity of the polymers. Chirality 9:593–600, 1997. © 1997 Wiley‐Liss, Inc.

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The title polymer can be applied as probe for chirality assignments of compounds such as (I)-(VI), using the circular dichroism fo the formed complexes. -(YASHIMA, E.; NIMURA, T.; MATSUSHIMA, T.; OKAMOTO, Y.; J. Am.