Ring-Over-Ring Deslipping From Imine-Bridged Heterorotaxanes

Abstract

Ring-over-ring slippage and ring-through-ring penetration are important processes in the construction of ring-in-ring multiple interlocked architectures. We have successfully observed “ring-over-ring deslipping” on the rotaxane axle by exploiting the dynamic covalent nature of imine bonds in imine-bridged heterorotaxanes R1 and R2 with two macrocycles of different ring sizes on the axle. When the imine bridges of R1 were cleaved, a hydrolyzed hetero[4]rotaxane [4]R1′ was formed as an intermediate under dynamic equilibrium, and the larger 38-membered macrocycle M was deslipped over the 24-membered ring (24C8 or DB24C8) to dissociate into a [3]rotaxane [3]R3 and a macrocycle M. The time dependent NMR measurement and the determined thermodynamic parameters revealed that the rate-limiting step of the deslipping process was attributed to steric hindrance between two rings and reduced mobility of M due to proximity to the crown ether, which was bound to the anilinium on the axle molecule.

Sequence‐controlled synthesis of rotaxanes

“…The half-life of the dethreading process was estimated to be 27 h at 303 K. Reproduced with permission. 129 Copyright 2022, Hoshino, Ono, and Kawai shuttling within a saturated [3]rotaxane with no empty recognition sites. Such ring-through-ring motion has the potential to control sequence complexity in heterorotaxanes, in spite of the fact that this initial example does not exhibit any sequence isomerism.…”

“…The large 38‐membered ring slips over the 24‐membered ring (DB24C8) and the stoppers of the rotaxane, resulting in dissociation to give a [3]rotaxane 70 and a 38‐membered ring free in bulk solution. The half‐life of the dethreading process was estimated to be 27 h at 303 K. Reproduced with permission 129 . Copyright 2022, Hoshino, Ono, and Kawai…”

“…More recently, Kawai and coworkers 129 synthesized a thermodynamically unstable hetero[4]rotaxane 69 to investigate (Figure 11B) its ring‐over‐ring slippage and dethreading from the dumbbell. Since the larger ring selected for this system is not trapped on the dumbbell, imine bonds were employed to temporarily fix the ring in place and allow the synthesis of a prerotaxane 68 containing two neighboring DB24C8 rings.…”

Dynamic Covalent Chemistry for Synthesis and Co‐conformational Control of Mechanically Interlocked Molecules

“…A series of doubly imine-bridged [2]rotaxanes were reported by the groups of Tsuji [110] and Suzuki. [111][112][113] The rotaxane thread 44 consists of a hydrindacene (1,2,3,5,6,7-hexahydro-s-indacene) skeleton with carbaldehyde groups in 2,6-position (Figure 11a). These easily undergo acid-catalyzed condensation with the two amino groups pointing towards the inside of the macrocycle 43.…”

“…A series of doubly imine‐bridged [2]rotaxanes were reported by the groups of Tsuji [110] and Suzuki [111–113] . The rotaxane thread 44 consists of a hydrindacene (1,2,3,5,6,7‐hexahydro‐ s ‐indacene) skeleton with carbaldehyde groups in 2,6‐position (Figure 11a).…”