Two-step modulation of ion recognition using a bis(saloph)-macrocyclic host having a 24-crown-8-like cavity

Non-threaded and rotaxane-type threaded wheel-axle assemblies consisting of dinickel(II) metallomacrocycle and dibenzylammonium axle

Rotaxanes are typically prepared using covalent bonds to trap a wheel component onto an axle molecule, and rotaxane-type wheel-axle assembly using only noncovalent interactions has been far less explored. Here we show that a dinickel(II) metallomacrocycle forms two different types of wheel-axle assemblies with a dibenzylammonium axle molecule based only on noncovalent interactions. The non-threaded assembly was obtained by introduction of Ni2+ into the macrocycle before the complexation with the axle molecule (metal-first method). The non-threaded assembly was in rapid equilibrium with each of the components in solution. The threaded assembly was obtained by introduction of Ni2+ after the formation of a pseudorotaxane from the non-metalated wheel and the axle molecule (axle-first method). The threaded assembly was not in equilibrium with the dissociated species even though it was maintained only by noncovalent interactions. Thus, formation of one of the non-threaded and threaded wheel-axle assemblies over the other is governed by the assembly pathway.

Rhodium-Catalyzed Asymmetric Macrocyclization towards Crown Ethers Using Hydroamination of Bis(allenes)

Enantiomerically enriched crown ethers (CE) exhibit strong asymmetric induction in phase transfer catalysis, supramolecular catalysis and molecular recognition processes. Traditional methods have often been used to access these valuable compounds, which limit their diversity and consequently their applicability. Herein, a practical catalytic method is described for the gram scale synthesis of a class of chiral CEs (aza-crown ethers; ACEs) using Rh-catalyzed hydroamination of bis(allenes) with diamines. Using this approach, a wide range of chiral vinyl functionalized CEs with ring sizes ranging from 12 to 36 have been successfully prepared in high yields of up to 92 %, dr of up to >20 : 1 and er of up to >99 : 1. These vinyl substituted CEs allow for further diversification giving facile access to various CE derivatives as well as to their three-dimensional analogues using ring-closing metathesis. Some of these chiral CEs themselves display high potential for use in asymmetric catalysis.

Enhancement of Alkali Metal Ion Recognition by Metalation of a Tris(saloph) Cryptand Having Benzene Rings at the Bridgeheads

A cryptand derivative, H₆L, which has three H₂saloph arms connected by two benzene ring bridgeheads, was synthesized and converted into the trinuclear metallocryptand, LNi₃. The nonmetalated host, H₆L, was found to bind to alkali metal ions (Na⁺, K⁺, Rb⁺, Cs⁺; logK_a = 3.37-6.67) in its well-defined cavity in DMSO/chloroform (1:9). The binding affinity was enhanced by 1-2 orders of magnitude upon the conversion into the metallocryptand, LNi₃, which can be explained by the more polarized phenoxo groups in the [Ni(saloph)] arms. The guest binding affinity of Na⁺ < K⁺ < Rb⁺ ≈ Cs⁺ was clearly demonstrated by the ¹H NMR competition experiments. The DFT calculations suggested that the Rb⁺ ion most suitably fit into the benzene-benzene spacing with a cation-π interaction and that only the largest Cs⁺ ion can almost equally interact with all six phenoxo oxygen donor atoms. The metallocryptand, LNi₃, also showed a strong binding affinity to Ag⁺ by taking advantage of cation-π interactions, which was confirmed by spectroscopic titrations and crystallographic analysis as well as DFT calculations. Thus, the well-defined three-dimensional cavity of LNi₃ was found to be suitable for strong binding with alkali metal ions as well as Ag⁺.

An N-linked disalicylaldehyde together with its caesium ion and dichloromethane sensing performances: ‘dual key & lock’ LMCT-enhanced fluorescence strategy

The disalicylaldehyde-Cs⁺sensing system, a novel approach for quick and reusable detection of Cs⁺together with convenient CH₂Cl₂monitoring.

Elucidating the secondary effect in the Lewis acid mediated anodic shift of electrochemical oxidation of a Cu(ii) complex with a N2O2 donor unsymmetrical ligand

The causes behind the fluctuations from a linear dependence of the electrochemical signal of a guest bound metalloligand [CuL] with the Lewis acidity of redox-inactive cations were established by using UV-vis spectroscopy and cyclic voltammetry.

A twisted macrocyclic hexanuclear palladium complex with internal bulky coordinating ligands

A macrocyclic hexanuclear palladium complex, which accumulates coordination sites on metals inside the cavity, was found to take a uniquely-twisted conformation when six molecules of a bulky pyridine derivative coordinated to the palladium.

Synthesis and Characterization of Alkali Metal Ion-Binding Copolymers Bearing Dibenzo-24-crown-8 Ether Moieties

Dibenzo-24-crown-8 (DB24C8)-bearing copolymers were synthesized by radical copolymerization using a DB24C8-carrying acrylamide derivative and N-isopropylacrylamide monomers. The cloud point of the resulting copolymers changed in aqueous solution in the presence of cesium ions. In addition, the ¹H NMR signals of DB24C8-bearing copolymers shifted in the presence of alkali metal. This shift was more pronounced following the addition of Cs⁺ compared to Rb⁺, K⁺, Na⁺, and Li⁺ ions due to recognition of the Cs⁺ ion by DB24C8.