title: A rational design for the directed helicity change of polyacetylene using dynamic rotaxane mobility by means of through-space chirality transfer.
abstract: Directed helicity control of a polyacetylene dynamic helix was achieved by hybridization with a rotaxane skeleton placed on the side chain. Rotaxane-tethering phenylacetylene monomers were synthesized in good yields by the ester end-capping of pseudorotaxanes that consisted of optically active crown ethers and sec-ammonium salts with an ethynyl benzoic acid. The monomers were polymerized with [{RhCl(nbd)}(2)] (nbd=norbornadiene) to give the corresponding polyacetylenes in high yields. Polymers with optically active wheel components that are far from the main chain show no Cotton effect, thereby indicating the formation of racemic helices. Our proposal that N-acylative neutralization of the sec-ammonium moieties of the side-chain rotaxane moieties enables asymmetric induction of a one-handed helix as the wheel components approach the main chain is strongly supported by observation of the Cotton effect around the main-chain absorption region. A polyacetylene with a side-chain rotaxane that has a shorter axle component shows a Cotton effect despite the ammonium structure of the side-chain rotaxane moiety, thereby suggesting the importance of proximity between the wheel and the main chain for the formation of a one-handed helix. Through-space chirality induction in the present systems proved to be as powerful as through-bond chirality induction for formation of a one-handed helix, as demonstrated in an experiment using non-rotaxane-based polyacetylene that had an optically active binaphthyl group. The present protocol for controlling the helical structure of polyacetylene therefore provides the basis for the rational design of one-handed helical polyacetylenes.
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1 (H126) Ookayama, Tokyo 152-8552, Japan.
authors.forename: Fumitaka
authors.initials: F
authors.lastname: Ishiwari
authors.forename: Kei-ichiro
authors.initials: K
authors.lastname: Fukasawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Sato
authors.forename: Kazuko
authors.initials: K
authors.lastname: Nakazono
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Koyama
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Takata
mesh_terms: D000042:Absorption; D000114:Acetylene / Q000031:analogs & derivatives* / Q000737:chemistry; D002942:Circular Dichroism; D043844:Crown Ethers / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D011108:Polymers / Q000737:chemistry*; D053279:Polyynes / Q000737:chemistry*; D017433:Protein Structure, Secondary; D043862:Rotaxanes / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D043844:Crown Ethers; D011108:Polymers; D043862:Rotaxanes; C044736:phenylacetylene; D053279:Polyynes; D000114:Acetylene