The influence of metal-complexing macrocycle size on intramolecular movement in rotaxanes

Abstract

New [2]rotaxanes composed of dibenzo-24-crown-8 wheel and the axle containing two metal-complexing 14- and/or 16-membered tetraazamacrocyclic units, coordinating the same or different metal ions (Ni and/or Cu) were synthesized and investigated.

Monosulfonated dibenzo-24-crown-8 and its properties

“…For this purpose, we have used axle 2 (Scheme 2), which contains a tetraazamacrocyclic complex unit of a family that has formerly been utilized for various DB24C8-containing rotaxanes. 14,15,19,25,26,61,62 Contrary to the experiments with neutral DB24C8, the new S DB24C8 wheel poses some synthesis challenges as it seems to decrease the stability of the enamine moiety in tetraazamacrocyclic axles. Nevertheless, in one of the attempts, the reaction of 2 , S DB24C8 − Bu 4 N + and 3,5-bis(trifluoromethyl)phenyl isocyanate resulted in rotaxane 3 (Scheme 2).…”

“…This mechanically interlocked molecule was identified by HRMS and NMR techniques, the latter revealing patterns of signals similar to those observed previously for rotaxanes of this type. 14,15,25,61…”

“…Dibenzo-24-crown-8 ether (DB24C8) is one of the iconic macrocycles in supramolecular chemistry. Its use in the assembly of pseudorotaxanes [1][2][3][4][5][6][7][8][9][10][11][12][13] and mechanically interlocked molecules (MIMs) [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] is widespread. The derivatives of DB24C8 play an equally important role; they are usually prepared by macrocyclization of the DB24C8 scaffold from appropriate pre-functionalized starting materials.…”

Electrochemically switchable rotaxanes: recent strides in new directions

“…9 shows [2]rotaxane 9 4+ which consists of an axle with a 14- and a 16-membered Ni II -complexing tetraazamacrocycle and a threaded dibenzo-24-crown-8 wheel. 65 In the initial state, the crown ether preferentially encircles the 14-membered ring since it is a stronger electron acceptor. However, the 16-membered Ni II complex shows a less positive oxidation potential at 1.15 V vs. Ag/AgCl as shown by differential pulse voltammetry.…”