title: Efficient end-capping synthesis of neutral donor-acceptor [2]rotaxanes under additive-free and mild conditions.
abstract: Efficient end-capping synthesis of neutral donor-acceptor (D-A) [2]rotaxanes without loading any catalysts or activating agents was achieved by utilizing high reactivity of a pentacoordinated hydrosilane toward salicylic acid derivatives. As components of [2]rotaxanes, an electron-deficient naphthalenediimide-containing axle with a salicylic acid terminus and several electron-rich bis(naphthocrown) ether macrocycles were employed. End-capping reactions with the pentacoordinated hydrosilane underwent smoothly even at low temperature to afford the corresponding [2]rotaxanes in good yields. A [2]rotaxane containing bis-1,5-(dinaphtho)-38-crown-10 ether as a wheel molecule was synthesized and isolated in 84% yield by the end-capping at -10 °C, presenting the highest yield ever reported for the end-capping synthesis of a neutral D-A [2]rotaxane. It was found that the yields of the [2]rotaxanes in the end-capping reactions were almost parallel to the formation ratios of the corresponding pseudo[2]rotaxanes estimated by utilizing model systems. These results indicate that the end-capping reaction using the pentacoordinated hydrosilane proceeded without perturbing the threading process, and most of the pseudo[2]rotaxanes underwent efficient end-capping reaction even at low temperature.
authors.affiliation: Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan), Fax: (+81) 3-5734-3543.
authors.forename: Yuya
authors.initials: Y
authors.lastname: Domoto
authors.forename: Shohei
authors.initials: S
authors.lastname: Sase
authors.forename: Kei
authors.initials: K
authors.lastname: Goto
keywords: donor-acceptor systems; rotaxanes; silanes; synthetic methods; template synthesis