Synthesis and Characterization of Poly[3]rotaxane through the Mizoroki-Heck Coupling Polymerization of Divinyl-functionalized [3]Rotaxane

Abstract

Main chain-type poly [3]rotaxanes were synthesized according to the rotaxanation-polymerization protocol by the polymerization of a divinyl [3]rotaxane monomer through the Mizoroki-Heck coupling with a diiodoarene. [3]Rotaxane 5 consisting of two monovinyl dibenzo-24-crown-8-ether wheels (2) and sec-ammonium salt (3) as an axle component was synthesized in 86% yield by a typical urethane end-capping reaction of the axle terminal hydroxyl group with bis(4-isocyanophenyl)methane in the presence of a catalytic amount of di-n-butyltin dilaurate. Quantitative N-acetylation of 5 yielded mono(vinylphenyl)-functionalized wheel-containing [3]rotaxane monomers 6. The mobility of the wheel components in [3]rotaxanes was evaluated by the two-dimention NOESY spectra of 5 and 6. The main-chain type poly[3]rotaxanes 8 were obtained in high yields by the Mizoroki-Heck-type polycondensation of 6 and diiodoarenes 7 in the presence of a palladium catalyst (Pd(OAc) 2 ). The structures of the polyrotaxanes were determined mainly by NMR and GPC, while the IR spectra showed that vinylene groups formed mainly took the trans configuration. Properties of the polyrotaxanes such as solubility and thermal stability were evaluated. Interlocked polymers, 1-20 a novel class of polymers containing mechanical linkages consisting of wheels and/or axle components, are expected to display unique properties such as mechanical and rheological ones. Among polyrotaxanes as one of the interlocked polymers (Figure 1) 34,35 are specially unique as characterized by their structural feature that the polymer main chain has no successive covalent bond. The repeating units of these polymers are bound by mechanical bonds. Meanwhile, there is few report on polyrotaxane with the backbone consisting of mechanical bonds, i.e., topologically linked polymer backbone, in contrast to poly[2]catenanes. [36][37][38][39][40][41][42][43][44][45][46] We previously reported the synthesis of poly[3]rotaxane utilizing the reversible cleavage-recombination process of the disulfide bond in the precense of a catalystic amount of thiol under thermodynamic control. 34 Further, we have recently disclosed the synthesis of poly[2]rotaxane by the polymerization of a bifunctional rotaxane monomer via the Sonogashira coupling reaction, 47 while a few poly[2]rotaxanes were synthesized by the thermaldynamic process. 21,22,[24][25][26][27][28] There are two possible ways accessing the main chain-type poly[3]-rotaxane: one goes through the initial rotaxanation followed by the polymerization (Figure 2, route A), whereas the other undergoes the initial coupling of wheel followed by the rotaxanation to poly[3]rotaxane (Figure 2, route B), as shown in Figure 1. Our previous paper 33 described the synthesis of a polyrotaxane by rotaxanation of ditopic wheel component utilizing the dynamic covalent chemistry of disulfide linkage, along Route B.In this paper, the synthesis of poly [3]rotaxanes by polycondensation via the Mizoroki-Heck coupling of diviynylfunctionalized [3]rotaxane and diiodoarenes,...

Synthetic strategies towards mechanically interlocked oligomers and polymers

“…85 Takata and co-workers have prepared homocircuit [3]rotaxanes (Fig. 24a) in which both macrocycle components contain either alkene or alkyne moieties for polymerisation by Mizoroki-Heck coupling 94 or [2 + 3] cycloaddition with nitrile N-oxides, 95 respectively, using appropriate di-functional linker reagents.…”

Crown Ether‐Based Polymeric Rotaxanes

“…Poly [3]rotaxanes reported by Takata and coworkers were synthesized using the first method described above, the host being a DB24C8 motif and the ditopic guest being a dialkylammonium PF 6 salt [27]. After blocking and acetylation of the salt, monomer 44 was formed and polymerization was carried out using the Mizoroki-Heck coupling reaction with both 1,4-diiodobenzene and 4,4 0 -diiodo-1,1 0 -biphenyl to yield polymers 45 and 46.…”

Mizoroki–Heck Cross‐Coupling of Acrylate Derivatives with Aryl Halides Catalyzed by Palladate Pre‐Catalysts

“…Palladium‐catalyzed cross‐coupling reactions are one of the most effective synthetic approaches for the construction of carbon–carbon bonds, sparking an ever‐growing demand for the development of new and more active catalysts, which can operate under mild conditions, Among these couplings, the Mizoroki–Heck reaction has emerged as a highly useful synthetic tool, widely used in the medicinal, fine‐chemical and polymer chemistry sectors, as well as in the synthesis of natural products . An interesting use of this strategy can be found in a the report by Jiang and co‐workers on the synthesis of a retinoid X receptor antagonist, diazepinylbenzoic acid, where the Mizoroki–Heck reaction was a determining step of the synthetic strategy .…”