Crown-cation complex effects. 15. Lariat ethers. 4. Chain length and ring size effects in macrocyclic polyethers having neutral donor groups on flexible arms

Abstract

We have recently reported the syntheses and certain binding properties of a class of molecules we call "lariat ethers".2"4 These compounds are characterized by a macrocyclic polyether ring and a flexible arm extending from the cycle to which are attached electron donor groups. Those compounds having arms joined by a methyleneoxy group appear to be relatively inflexible and exhibit both relatively weak and solvent-dependent cation binding.2•3 In contrast, when the secondary donor arm is attached to a nitrogen pivot rather than at carbon, binding constants are found to be substantially increased over simple monocyclic systems.4 We now wish to report three important findings regarding the cation binding of the highly flexible nitrogen lariat systems. First, the expected ring size-cation diameter correlation does not appear to be as significant for these cases as for others.5 Rather, binding constants reflect the total number of oxygens present both in the ring and the side arm and seem little affected by the presence of endocyclic nitrogen. Second, the Na+ binding constants peak when

Copper(ii) complexes of quinoline polyazamacrocyclic scorpiand-type ligands: X-ray, equilibrium and kinetic studies

“…The pH was adjusted with NaOH to values at which the formation of the CuL 2+ complexes in solution is complete. Complex decomposition was started by adding an excess of an HClO 4 solution of suitable concentration containing the required amount of NaClO 4 for maintaining a constant ionic strength of 0.15 M. For the kinetic studies on complex formation, a 5 × 10 −4 M solution of the ligand whose pH had been previously adjusted with HClO 4 and NaOH was mixed in the stopped-flow instrument with a solution at the same pH and containing the same concentration of Cu…”

“…9 Crystals of [CuL1](ClO 4 ) 2 ·H 2 O suitable for X-ray diffraction were grown by slow evaporation of 10 −3 M aqueous solutions of Cu(ClO 4 ) 2 ·6H 2 O and L1·4HCl in the presence of an excess of NaClO 4 at an initial pH of 5. Unfortunately, attempts with the L2 complex were unsuccessful.…”

“…Water was twice distilled and passed through a Millipore apparatus. All solutions were prepared 0.15 mol dm −3 in NaClO 4 . The pH values were measured with a Mettler-Toledo MP-120 pHmeter and adjustments of the hydrogen ion concentration of the solutions were made with diluted HCl and NaOH solutions.…”

Bioorganic Chemistry

“…* These compounds are characterized by a macrocyclic polyether ring and a flexible arm extending from the cycle to which are attached electron donor groups (299). Gokel (University of Miami) introduced a new class of crown ether, called lariat crown ethers.…”

Metal Complexes with Macrocyclic Ligands. Part XLI. Nickel(II) and copper(II) complexes with mono‐N‐functionalized dithiadiazamacrocycles

“…Although examples of functionalized ligands of both types have been described for crown ethers [6], for N,O macrocycles [7], and polyaza cycloalkanes [2], much less is known about the properties of functionalized thiaaza systems. Examples of it can be found in N,S macrocycles, which have been substituted at the N-atoms by two acetate groups [8] or by two 2-methylpyridyl side chains [9].…”