Synthesis of acetylene-functionalized [2]rotaxane monomers directed toward side chain-type polyrotaxanes

Abstract

A crown ether-ammonium salt-type rotaxane monomer was synthesized in a high yield using dibenzo-24-crown-8-ether and sec-ammonium salt having a hydroxy terminal by means of an end-capping reaction with an ethynyl benzoic acid. Its N-acetylated derivative was also synthesized in a quantitative yield using excess acetic anhydride and triethylamine. Novel side chain-type polyrotaxanes, that is, ammonium-type and neutral polyphenylacetylenes tethering rotaxane moieties in side chains with high molecular weights, were obtained in high yields by polymerizations with an Rh catalyst. The structures of the polymers were characterized by infrared, ultraviolet-visible (UV-vis) spectra and size exclusion chromatography. N-acetylation of the rotaxane moieties of the ammonium salt-type polymer resulted in the formation of a reddish-colored neutral polymer showing red-shifted UV-vis absorptions around 500 nm based on the conjugated main chain, according to the structural change of rotaxane side chains, that is, the change of the distance of the wheel component to the polyacetylene main chain. The solubility of the polymers was evaluated.

A Rational Design for the Directed Helicity Change of Polyacetylene Using Dynamic Rotaxane Mobility by Means of Through‐Space Chirality Transfer

“…[12] The various polyacetylenes were prepared by polymerization of the monomers with a typical polymerization catalyst [{RhClA C H T U N G T R E N N U N G (nbd)} 2 ]/Et 3 N in CHCl 3 (in DMF for 4; nbd = norbornadiene) at room temperature for 4 h (Scheme 3). [9,13] Despite the presence of sec-ammonium salt groups, [9,14] polymerization of all monomers proceeded successfully to give the corresponding polyacetylenes poly-(S)-1, poly-(R)-2, poly-(S)-2, poly-(R,R)-3, and poly-4 in high yields (89-98 %). The polymers were isolated by reprecipitation from Et 2 O.…”

“…Monomers (S)-1, (R)-2, (S)-2, and A C H T U N G T R E N N U N G (R,R)-3 were prepared in yields of 22-77 % according to a tributylphosphane-catalyzed ester end-capping protocol (Scheme 2 and Scheme 3). [9,11] Non-rotaxanetype monomer 4, which lacks a wheel component, was prepared as a reference monomer. The structures of these monomers were determined by www.chemeurj.org UV/Vis, circular dichroism (CD), and FAB HRMS spectroscopy.…”

“…We attempted to estimate the molecular weights of the polymers by size-exclusion chromatography (SEC); however, their values were too high to measure correctly (M n > 2.0 10 6 ). [9] Large-molecular-weight polyacetylenes are not unusual.…”

“…[9,16] The polymers were isolated by re-precipitation from MeOH rather than Et 2 O, due to the increase in solubility in ordinary organic solvents induced by N-acylation. We attempted to estimate the molecular weights of the polymers by size-exclusion chromatography (SEC); however, their values were too high to measure correctly (M n > 2.0 10 6 ).…”

“…[8] We became intrigued by the possibility of directed structure control of the polyacetylene dynamic helix by hybridization with rotaxane placed on the side chain, which we would accomplish by controlling the mobility of the rotaxane components-a reasonable next step for us, as we had already achieved the regular arrangement of rotaxane functions in the synthesis of side chain-type polyrotaxanes. [9] Masuda et al…”