Controllable Topological Transformations of 818 Molecular Metalla-knots by Oxidation of Thiazole-Based Ligands

By exploiting coordination-driven self-assembly, high yields of two 8₁₈ molecular metalla-knots could be obtained using a thiazole-moiety-containing asymmetric dipyridyl ligand 2-(pyridin-4-yl)-5-(pyridin-4-ylethynyl)benzo[d]thiazole ( L₁ ), as confirmed using X-ray crystallographic analysis, electrospray ionization-time-of-flight/mass spectrometry (ESI-TOF/MS), and detailed liquid-state nuclear magnetic resonance (NMR) spectroscopy. To modulate the self-assembled structures, m-chloroperbenzoic acid (m-CPBA) was utilized to oxidize thiazole-based ligand L₁ to N-thiazole-oxide-based ligand 2-(pyridin-4-yl)-5-(pyridin-4-ylethynyl)benzo[d]thiazole 3-oxide ( L₂ ), which enabled the selective construction of the corresponding tetranuclear macrocycles. Notably, two molecular metalla-knots could be topologically transformed from 8₁₈ knots to simple monocycles because the L₁ alkyne bond was inert toward m-CPBA, as confirmed by liquid-state NMR spectroscopy, ESI-TOF/MS, and elemental analysis.