From Hierarchical Helicates to Functional Supramolecular Devices

Abstract

Catechol ligands with aldehyde, ketone or ester groups attached in 3‐position form, in the presence of titanium(IV) triscatecholate, titanium(IV) complexes. If lithium cations are the counterions, they can bind in a successive step to the salicylate units of the complex and form a dimeric triple‐lithium‐bridged dinuclear helicate. In solution, the dimer is in equilibrium with the monomer and the thermodynamics of the dimerization can be easily evaluated. Thus, the hierarchically assembled titanium(IV) helicates represent a lithium‐dependent molecular switch. The investigation of different derivatives of the complex allows for an estimation of the influence of side chain functionalities on the energetics of the dimerization. Thus, the hierarchically assembled helicates can be used as a kind of molecular balance to determine weak interaction energies (solvophobic effects and even dispersive effects). In addition, tethering of two ligands leads to “classical” helicates. Removal or addition of lithium cations allows for a reversible switching between a compressed and expanded state, which in the case of chiral ligands can be even performed stereospecifically.

Cavity-Containing [Fe2L3]4+ Helicates: An Examination of Host-Guest Chemistry and Cytotoxicity

“…Systems have been studied for their anti-cancer and anti-microbial activity and their potential as drug delivery agents. Helicates ( Piguet et al, 1997 ; Albrecht, 2001 ; Hannon and Childs, 2004 ; Howson and Scott, 2011 ; Boiocchi and Fabbrizzi, 2014 ; Paneerselvam et al, 2018 ; Albrecht et al, 2019 ; Albrecht, 2020 ; Tran and Yoo, 2020 ) are one of the earlier known and well-studied sub-classes of MSAs. Lehn and co-workers reported the first helicates; a double-stranded dinuclear and larger trinuclear system were generated from poly(2,2′-bipyridine) ligands and Cu(I) ions ( Lehn et al, 1987 ) Subsequently, single, triple, and quadruple stranded helicates have all been synthesized and these systems are chiral featuring P (plus, right-handed) and M (minus, left-handed) helices ( Figure 1 ).…”

Bis(catecholato-κ2 O,O′)bis(dimethyl sulfoxide-κO)titanium(IV)

“…A number of heteroleptic mono-and multi-nuclear titanium complexes do contain titanium catechol units (Sakata et al, 2010;Bazhenova et al, 2016;Sonstro ¨m et al, 2019;Passadis et al, 2020) (for further examples, see Database survey below). Most prominently, titanium tris-catecholates have been used as versatile building blocks in a range of supramolecular, oligonuclear homo-and hetero-metal-ligand cluster assemblies (Bru ¨ckner et al, 1998;Caulder et al, 2001;Albrecht et al, 2008Albrecht et al, , 2019.…”

Kationen‐gesteuerte Bildung und Umwandlung der fac/fac‐ und mer/mer‐Stereoisomere eines dreisträngigen Helicats

“…Diese wollen wir in unsere Untersuchungen zu Helicat-basierten Schaltern fürReaktions-und Selektivitätskontrolle einschließen. [24] Danksagung Wirbedanken uns fürd ie Unterstützung von X.C.durch das Chinese Scholarship Council. Wirdanken auch Dr. Christoph Räuber fürd ie Hilfe bei den NMR-Studien.…”

“…Diesem Konzept folgend sollten wir verwandte schaltbare Systeme finden können. Diese wollen wir in unsere Untersuchungen zu Helicat‐basierten Schaltern für Reaktions‐ und Selektivitätskontrolle einschließen …”