Helical Polyacetylenes Induced via Noncovalent Chiral Interactions and Their Applications as Chiral Materials

Abstract

Construction of predominantly one-handed helical polyacetylenes with a desired helix sense utilizing noncovalent chiral interactions with nonracemic chiral guest compounds based on a supramolecular approach is described. As with the conventional dynamic helical polymers possessing optically active pendant groups covalently bonded to the polymer chains, this noncovalent helicity induction system can show significant chiral amplification phenomena, in which the chiral information of the nonracemic guests can transfer with high cooperativity through noncovalent bonding interactions to induce an almost single-handed helical conformation in the polymer backbone. An intriguing ''memory effect'' of the induced macromolecular helicity is observed for some polyacetylenes, which means that the helical conformations induced in dynamic helical polyacetylene can be transformed into metastable static ones by tuning their helix-inversion barriers. Potential applications of helical polyacetylenes with controlled helix sense constructed by the ''noncovalent helicity induction and/or memory effect'' as chiral materials are also described.

Stereochemical enhancement of polymer properties

“…The dynamic and helical memory properties of polyacetylene have been leveraged for the same application but with the added advantage of a switchable chirality to potentially alter the elution order of the enantiomers. 203,204 Another interesting property of helical polymers is the amplification of optical activity from monomer to polymer, due to the synergistic effect with the helical backbone, as observed in metal-complexed helical polymers where an induced enantioselectivity was observed. 205,206 When applying this principle to dynamic helical polymers it is possible to produce an asymmetric catalyst with switchable enantioselectivity (Figure 4).…”

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

“…Since the P and M forms are in dynamic equilibrium, we can change the P/M equilibrium ratio by the addition/removal or modification of the chiral auxiliary. This would lead to responsive helicity changes and inversions as described the Section 1.3, which are recognized as one of the hot topics in functional molecular chemistry [18][19][20][21][22][23][24]. ( Figure 3a), we have to convert the enantiomer pair into a diastereomer pair by the introduction of a chiral auxiliary.…”

“…To date, various types of chemical and other stimuli have been used to achieve dynamic helicity inversion of the helical structures such as polymers, metal helicates, etc. [18][19][20][21][22][23][24]. …”

Macromolecular helicity induction and static helicity memory of poly(biphenylylacetylene)s bearing aromatic pendant groups and their use as chiral stationary phases for high‐performance liquid chromatography

“…Okamoto et al achieved the first asymmetric synthesis of a one‐handed helical poly(triphenylmethyl methacrylate) (PTrMA) 20–25 by the helix‐sense‐selective polymerization of an achiral bulky vinyl monomer with a chiral catalyst in 1979 and discovered its remarkable chiral separation ability when used as a CSP for HPLC, which was then commercialized in 1982 as the first practical helical polymer‐based CSP. Since then, a variety of CSPs consisting of one‐handed helical polymers, including polyacetylenes 26–34 and polyisocyanides, 35–38 have been developed 25,39,40 . Among the helical polymers, the helical polysaccharide derivatives (e.g., cellulose and amylose derivatives) 25,41–44 developed by Okamoto et al are recognized as the most used commercially available CSPs in the world.…”