Probing the Dynamics of the Imine-Based Pentafoil Knot and Pentameric Circular Helicate Assembly

Abstract

We investigate the self-assembly dynamics of an imine-based pentafoil knot and related pentameric circular helicates, each derived from a common bis(formylpyridine)bipyridyl building block, iron(II) chloride, and either monoamines or a diamine. The mixing of circular helicates derived from different amines led to the complete exchange of the N-alkyl residues on the periphery of the metallo-supramolecular scaffolds over 4 days in DMSO at 60 °C. Under similar conditions, deuterium-labeled and nonlabeled building blocks showed full dialdehyde building block exchange over 13 days for open circular helicates but was much slower for the analogous closed-loop pentafoil knot (>60 days). Although both knots and open circular helicates self-assemble under thermodynamic control given sufficiently long reaction times, this is significantly longer than the time taken to afford the maximum product yield (2 days). Highly effective error correction occurs during the synthesis of imine-based pentafoil molecular knots and pentameric circular helicates despite, in practice, the systems not operating under full thermodynamic control.

Multi-stimuli Control over Assembly and Guest Binding in Metallo-supramolecular Hosts Based on Dithienylethene Photoswitches

“…Increasing such a system’s complexity via the introduction of multiple different ligands is challenging, since metal-mediated self-assembly under thermodynamic control easily results in a statistical mixture of products. 7 In recent years, several strategies to combine distinguishable ligands in a non-statistical fashion, leading to the clean assembly of heteroleptic cages, have been reported. For example, the Yoshizawa group explored the use of a templating guest, 8 Crowley et al took advantage of hydrogen-bonding between adjacent ligands, 9 and Zhou, 10a Fujita, 10b Mukherjee, 10c , 10d Chand, 10e , 10f and our group 10g − 10i utilized geometric principles to form heteroleptic cages containing two different types of ligands.…”

Introducing Seven Transition Metal Ions into Terpyridine-Based Supramolecules: Self-Assembly and Dynamic Ligand Exchange Study

“…However, it remains a formidable challenge to characterize the dynamic process with multiple possible intermediates and processes involved at different concentration, temperature, time, etc. To date, only a few examples have been reported with the aid of NMR, mass spectrometry (MS), fluorescence-resonance energy transfer (FRET), and other methods . In this report, we studied the kinetics of the dynamic ligand exchange process of assembled hexameric fractals using mass spectrometry (Figure b).…”

Controlling the Complexity and Interconversion Mechanisms in Self‐Assembled [Fe2L3]4+ Helicates and [Fe4L6]8+ Cages

“…Metallosupramolecular assemblies, which are generally self‐assembled under thermodynamic control from labile metal ions and suitable symmetric bridging ligands, [6] have shown a range of structural reconfigurations (involving the rupture and reforming of multiple coordination bonds) in response to light, [7] mechanical force, [8] pH, [9] guest molecules, [6a, 10] the addition of reagents, [11] temperature, [6b, 12] solvent [13] or concentration effects [14] . Although many can be rationalized in terms of geometric and thermodynamic parameters, [15] the mechanisms [16] of the transformations have not been extensively investigated.…”