Multicomponent Self-Assembled Metal–Organic [3]Rotaxanes

Abstract

A set of environmentally responsive metal-organic [3]rotaxanes is described. These mechanically interlocked macromolecules may be prepared in quantitative yield via a one-pot procedure involving treatment of a flexible tetracationic macrocycle, known as the Texas-sized molecular box, with tri-1,3,5-benzenetricarboxylate anion and silver cations (Ag(+)). The use of this three-component mixture gives rise to a metal-organic [3]rotaxane via a self-assembly process that occurs under ambient conditions in DMSO-d6 solution. The complex is stable in the presence of excess TFA. However, disassembly of the [3]rotaxane to produce anion-box associated entities may be triggered by adding a competitive counteranionic species (e.g., I(-)). Adding excess Ag(+) serves to reverse this decomplexation process. The nature of the [3]rotaxane complex could be fine-tuned via application of an external stimulus. Increasing the temperature or adding small molecules (e.g., D2O, methanol-d4, acetonitrile-d3, DMF-d7, acetone-d6, or THF-d8) to the initial DMSO-d6 solution induces conformational flipping of the macrocycle within the overall complex (e.g., from limiting chair to chairlike forms). Support for the molecular stimuli responsive nature of the various structures came from solution-phase one- and two-dimensional ((1)H, 1D and 2D NOESY) NMR spectroscopic studies carried out in DMSO-d6. The core metal-linked rotaxane unit was characterized via single-crystal X-ray diffraction analysis. Initial evidence that the present self-assembly process is not limited to the use of the Ag(+) cation came from studies involving Cd(2+); this replacement results in formation of 2D metal-organic rotaxane-containing frameworks (MORFs).

Hypervalent Iodine Based Reversible Covalent Bond in Rotaxane Synthesis

“…This is especially true for the rotaxane synthesis, as only a few approaches have been used up to now. These include the ring closing metathesis, formation of imine and disulfide bonds, and reversible metal–organic bonds, which highlight the need for novel approaches to rotaxane synthesis.…”

Imidazolium Based Probes for Recognition of Biologically and Medically Relevant Anions

“…Sessler et al have synthesized number of texas sized tetracationic macrocycles 80–83 and have studied the formation of environmentally responsive host‐guest structures with aromatic diacarboxylic acids viz. terephthalic acid ( 84 ), 4,4’‐biphenyl dicarboxylic acid ( 85 ) and 2,6‐naphthalene dicarboxylic acid ( 86 ) and their mono and dianions.…”

“…The addition of small inorganic anions like Cl − as their TBA salts to the solution of preformed [ 80 • 86DA ] 2+ complex replaced the dianion 86DA from the cavity of the 80 and formed 1:1 and 1:2 complex between 80 and Cl − with gradual addition of six equivalents of TBA Cl − . However, NO 3 − anion formed only 1:1 stoichiometric complex with 80 and process of complex formation was completed only on addition of 20 equivalents of TBA NO 3 salt.…”

Statistical Mechanical Model of Gas Adsorption in a Metal-Organic Framework Harboring a Rotaxane Molecular Shuttle

“…In a [2]rotaxane molecular shuttle, the wheel is free to translate along the axle, which can be decorated with functional groups that serve as "stations" for the wheel, possibly with different affinities for it. Pioneering experimental studies have demonstrated the integration of rotaxanes into MOF scaffolds, [35][36][37][38][39][40][41][42][43][44][45][46] but resultant adsorption properties have not been investigated.…”