1262997-19-2Relevant academic research and scientific papers
Thermoresponsive shuttling of rotaxane containing trichloroacetate ion
Abe, Yoko,Okamura, Hisashi,Nakazono, Kazuko,Koyama, Yasuhito,Uchida, Satoshi,Takata, Toshikazu
, p. 4122 - 4125 (2012/10/07)
A thermoresponsive rotaxane shuttling system was developed with a trichloroacetate counteranion of an ammonium/crown ether-type rotaxane. Chemoselective thermal decomposition of the ammonium trichloroacetate moiety on the rotaxane yielded the corresponding nonionic rotaxane accompanied by a positional change of the crown ether on the axle. The rotaxane skeleton facilitated effective dissociation of the acid, markedly lowering the thermal decomposition temperature.
Neutralization of a sec-ammonium group unusually stabilized by the "rotaxane Effect": Synthesis, structure, and dynamic nature of a "free" sec-amine/crown ether-type rotaxane
Nakazono, Kazuko,Takata, Toshikazu
experimental part, p. 13783 - 13794 (2011/02/28)
A fifteen-year riddle has been settled: neutralization, the most popular chemical event, of a crown ether/sec-ammonium salt-type rotaxane has been achieved and a completely nonionic crown ether/sec-amine-type rotaxane isolated. A [2]rotaxane was prepared as a typical substrate from a mixture of dibenzo[24]crown-8 ether (DB24C8) and sec-ammonium hexafluorophosphate (PF 6) with a terminal hydroxy group through end-capping with 3,5-dimethylbenzoic anhydride in the presence of tributylphosphane as a catalyst in 90 % yield. A couple of approaches to the neutralization of the ammonium rotaxane were investigated to isolate the free sec-amine-type rotaxane by decreasing the degree of thermodynamic and kinetic stabilities. One approach was the counteranion-exchange method in which the soft counterion PF 6- was replaced with the fluoride anion by mixing with tetrabutylammonium fluoride, thus decreasing the cationic character of the ammonium moiety. Subsequent simple washing with a base allowed us to isolate the free sec-amine-type rotaxane in a quantitative yield. The other approach was a synthesis based on a protection/deprotection protocol. The acylation of the sec-ammonium moiety with 2,2,2-trichloroethyl chloroformate gave an N-carbamated rotaxane that could be deprotected by treating with zinc in acetic acid to afford the corresponding free sec-amine-type rotaxane in a quantitative yield. The structure of the free sec-amine-type rotaxane was fully confirmed by spectral and analytical data. The generality of the counteranion-exchange method was also confirmed through the neutralization of a bisammonium-type [3]rotaxane. The mechanism was studied from the proposed potential-energy diagram of the rotaxanes with special emphasis on the role of the PF 6- counterion. Neutral and free: The neutralization of the ammonium group of crown ether/sec-ammonium salt-type rotaxanes is a simple, yet important issue, which had not been solved to date. Neutral rotaxanes had not been isolated because of their unusual stability; however, the successful synthesis of free amine-type rotaxanes has now been achieved. The key to canceling this strong stabilization is the construction of a multiple equilibrium system and the successful removal of the conjugate acid from the reaction system (see scheme). Copyright
