The relationship between the conformational degree of freedom of template-containing threads and slippage in the formation of [2]rotaxane building blocks

Abstract

A straightforward slippage strategy has been used for the synthesis of three [2]rotaxane building blocks that all contain an ammonium template for the dibenzo-24-crown-8 macrocycle and an N-hydroxysuccinimide end. The kinetic rate of the slipping-on process proved to be highly dependent on both the length and flexibility of the thread.

Weinreb Amide as Secondary Station for the Dibenzo‐24‐crown‐8 in a Molecular Shuttle

“…in 7, H 12 and H 13 are shifted downfield with Δδ = 0.56 and 0.45 ppm, respectively) or shielded by the aromatic rings of DB24C8 (i.e. in 7, H 15 , H 17 , H 18 and H 19 are shifted upfield with Δδ = -0.33, -0.31, -0.21 and -0.21 ppm, respectively).…”

The Importance of Length and Flexibility of Macrocycle‐Containing Molecular Translocators for the Synthesis of Improbable [2]Rotaxanes

“…After cleavage of the active-ester-containing axle of rotaxane 14 by using N-methyl-tert-butylbenzylamine, the interlocked architecture of the improbable rotaxane 16 was evidenced by comparison of the 1 HNMR spectra of the DB24C8 macrocycle, the rotaxane 16,a nd its non-interlocked axle analogue 16 u (Figure 4a-c) (see the Supporting Information for the 1 HNMR evidences of rotaxane 15). In the interlockedc ompound 16, signals of the hydrogen atoms H A-E of the DB24C8 macrocycle were all split with respectt ot he free DB24C8m acrocycle because of their non-equivalence, which wasd ue to the threading of the non-symmetrical axle (Figure 4a-b).…”

“…We recently correlated the flexibility of the translocators 1 u – 4 u with the rate and efficiency of the slipping‐on of the DB24C8 macrocycle around them (Scheme and Figure , step 1) . Dried rotaxane translocators 1 – 4 could be isolated at room temperature as stable supramolecular edifices and stored over time without any self‐disassembly.…”

“…We recently correlated the flexibility of the translocators 1u-4u with the rate and efficiency of the slipping-on of the DB24C8 macrocycle around them (Scheme 1a nd Figure 1, step 1). [15] Dried rotaxanet ranslocators 1-4 could be isolated at room temperature as stable supramolecular edificesa nd stored over time without any self-disassembly.W en ow report the synthesis of rotaxanes without any recognitione lement between the macrocycle and the thread, and we have investigated the correlation between efficacyo ft he strategy with the nature andl ength of both the translocator and the targeted axle. With this aim, four different translocators 1-4 (Scheme 1) and two different targeted axles 15 and 16 to be encircled (Scheme 3) werec onsidered.…”

How Secondary and Tertiary Amide Moieties are Molecular Stations for Dibenzo-24-crown-8 in [2]Rotaxane Molecular Shuttles?

“…Instead, the next hydrogen atoms H 11 and H 12 are. One might suggest that both the cis - trans isomerism of the next tertiary amide and the rotation of the N-C 16 σ bond, which occur quickly at room temperature [ 61 ], allow for the presence of isomers in which steric repulsions prevent the DB24C8 from interacting optimally with the most acidic hydrogens H 13 ( Figure 5 b). The DB24C8 is therefore sterically forced to interact with the neighboring less acidic but less hampered hydrogen atoms.…”