[2]Rotaxanes comprising a macrocylic Hamilton receptor obtained using active template synthesis: synthesis and guest complexation

<p>A macrocyclic ring comprising multiple hydrogen-bonding sites as well as metal-chelating sites is shown to play the role of ligand in active templated, copper-catalysed [2]rotaxane formation via Huisgen and Glaser reactions. The crystallographic structure and copper ion binding studies are provided for the free macrocycle, along with molecular modelling, barbital, N,N′-trimethyleneurea and copper (I) binding information for the new rotaxanes.</p

Reversible Photocapture of a [2]Rotaxane Harnessing a Barbiturate Template

Photoirradiation of a hydrogen-bonded molecular complex comprising acyclic components, namely, a stoppered thread (<b>1</b>) with a central barbiturate motif and an optimized doubly anthracene-terminated acyclic Hamilton-like receptor (<b>2b</b>), leads to an interlocked architecture, which was isolated and fully characterized. The sole isolated interlocked photoproduct (Φ = 0.06) is a [2]­rotaxane, with the dimerized anthracenes assuming a head-to-tail geometry, as evidenced by NMR spectroscopy and consistent with molecular modeling (PM6). A different behavior was observed on irradiating homologous molecular complexes <b>1</b>⊂<b>2a</b>, <b>1</b>⊂<b>2b</b>, and <b>1</b>⊂<b>2c</b>, where the spacers of <b>2a</b>, <b>2b</b>, and <b>2c</b> incorporated 3, 6, and 9 methylene units, respectively. While no evidence of interlocked structure formation was observed following irradiation of <b>1</b>⊂<b>2a</b>, a kinetically labile rotaxane was obtained on irradiating the complex <b>1</b>⊂<b>2c</b>, and ring slippage was revealed. A more stable [2]­rotaxane was formed on irradiating <b>1</b>⊂<b>2b</b>, whose capture is found to be fully reversible upon heating, thereby resetting the system, with some fatigue (38%) after four irradiation–thermal reversion cycles

Remote Photoregulated Ring Gliding in a [2]Rotaxane via a Molecular Effector

A molecular barbiturate messenger, which is reversibly released/captured by a photoswitchable artificial molecular receptor, is shown to act as an effector to control ring gliding on a distant hydrogen-bonding [2]­rotaxane. Thus, light-driven chemical communication governing the operation of a remote molecular machine is demonstrated using an information-rich neutral molecule

Formation of a Hydrogen-Bonded Barbiturate [2]-Rotaxane

Interlocked structures containing the classic Hamilton barbiturate binding motif comprising two 2,6-diamidopyridine units are reported for the first time. Stable [2]-rotaxanes can be accessed either through hydrogen-bonded preorganization by a barbiturate thread followed by a Cu⁺-catalyzed “click” stoppering reaction or by a Cu²⁺-mediated Glaser homocoupling reaction