Ligandstruktur und Komplexierung, XXI: Nichtcyclische Kronenether mit zentraler Pyridin‐Einheit und starren Donorendgruppen

Abstract

Synthese und Eigenschaften neuer nichtcyclischer Neutralliganden vorn Kronenethertyp werden beschrieben. Charakteristische Strukturmerkmale sind zentrale Pyridin-Einheiten sowie starre donorpihige Endgruppen. Die Kronenether-Eigenschaften ergeben sich aus der Flhigkeit der Liganden, stochiometrische, kristalline Komplexe mit Alkali-, Erdalkali-und SchwermetallKationen zu bilden; einige davon enthalten Wasser in stochiometrischen Anteilen. NMR-Spektren zeigen, daB im gelosten Komplex helikale Ligandkonformationen vorliegen. Die Temperaturahhlngigkeit der NMR-Spektren wird durch Dissoziations-Rekombinations-Gleichgewichte bzw. Konformationsanderungen der Komplexe gedeutet. Ligand Structure and Complexation, XXI Noncyclic Crown Ethers with Central Pyridine Units and Rigid Donor End GroupsSynthesis and properties of new noncyclic neutral ligands of the crown ether type are described. Characteristic structural elements are central pyridine units and rigid end groups which function as additional donor centers. The crown ether properties result from the ability of the ligands to form stoichiometric crystalline complexes with alkaline, alkaline earth, and heavy metal ions. Some of the complexes contain water in stoichiometric proportions. NMR spectra lead to the assumption of helical ligand conformations in the dissolved complexes. The temperature dependance of the NMR spectra are interpreted by dissoziation-recombination-equilibria and conformational changes in the complexes, respectively.

Helicates as Versatile Supramolecular Complexes

“…The helical twist may be favored by the attachment of rigid and bulky terminal aromatic groups to oligo(ethylene glycol) units ) . The P ↔ M interconversion process may be slowed down by using (i) a more rigid organic backbone as in the carbocyclic helicene 18 73 whose single-stranded helical complex [Na( 18 )] + racemizes slowly at room temperature, and (ii) a strongly bound and inert metal ion which prevents dissociative pathways for helical interconversion as found in the inert cyclometallated Pt(II) complex 19 …”

“…The P ↔ M interconversion process may be slowed down by using (i) a more rigid organic backbone as in the carbocyclic helicene 18 73 whose single-stranded helical complex [Na( 18 )] + racemizes slowly at room temperature, and (ii) a strongly bound and inert metal ion which prevents dissociative pathways for helical interconversion as found in the inert cyclometallated Pt(II) complex 19 4

13 Configurational interconversion between P and M helical enantiomers of [Na( 17 )] +

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“…69 Compounds 15 and 16 react with Rb + to give helically twisted mononuclear complexes [Rb(15)] + 70 and [Rb- (16)] + 71 in the solid state while 1 H and 13 C NMR spectra of the analogous complex [Na (17)] + indicate that P-and M-helices interconvert rapidly on the NMR time scale at room temperature (∆G q ≈ 41 kJ mol -1 , Figure 13). 72 The P T M interconversion process may be slowed down by using (i) a more rigid organic backbone as in the carbocyclic helicene 18 73 whose single-stranded helical complex [Na(18)] + racemizes slowly at room temperature, and (ii) a strongly bound and inert metal ion which prevents dissociative pathways for helical interconversion as found in the inert cyclometallated Pt(II) complex 19. 74 Constable and co-workers [61][62][63][64] and Potts and coworkers 60 have shown that the quinquepyridine 7 and its substituted analogues 20-22 and 24-28 may act as pentadentate ligands with transition metal ions to give mononuclear single-stranded helical complexes.…”

Controlling surface properties and permeability of polyglycerol network films

“…In such materials, the type of chain segments, the polymer network architecture and the number of covalent crosslinks affect material properties. In some cases, interactions with ions can introduce additional physical netpoints by pseudo‐crown ether structures . However, a general feature associated with the advantageous hydrophilicity of polyether networks is their massive swelling and softness, which may not be anticipated for all applications.…”

Solution cation-binding properties of segmented polyethylene oxide-A13C NMR spectroscopic study

“…The metal-ion complexation with oligoethylene glycols of different lengths endcapped with various units like 8-hydroxyquinoline, 2-methoxy phenol, and so forth, were also investigated in solution by UV and NMR techniques. [13][14][15] Otera et al studied the complexation of dimethyl tin dichloride with glymes and phenyl capped oligoethylene glycols using 119 Sn NMR spectroscopy. 16 The change in ␦ values of the Sn nucleus upon complexation was used to evaluate their binding properties.…”