Crown Ether Complexes Research Articles

Crown ether complexes of sodium and potassium 2-(benzotriazol-2-yl)phenolates: Synthesis and catalysis towards the ring-opening polymerization of rac-lactide

ABSTRACTCrown ether complexes of sodium and potassium 2-(benzotriazol-2-yl)phenolates were synthesized and characterized. In the presence of BnOH these complexes are highly active catalysts for the...

Cation‐ and Solvent‐Induced Supramolecular Aggregation Studies of Crown Ether‐Containing Dinuclear Alkynylgold(I) Isocyanide Complexes

A series of crown ether‐based dinuclear bis(alkynyl)‐bridged gold(I) isocyanide complexes has been designed, synthesized, and characterized. The intramolecular Au···Au interactions of these complexes are used to bind potassium ions. Most of the bis(crown ether)‐containing gold(I) complexes are found to obey the 1:1 binding mode towards K+. Upon addition of K+ ions, the sandwich complex of crown ether can be formed, which brings the two gold(I) centers into close proximity, resulting in the switching on of the Au···Au interaction. The influence of the length of the bridging ligands between the two AuI centers has also been studied. Apart from the potassium ion‐induced intramolecular assembly, intermolecular Au···Au interactions of the crown ether‐containing dinuclear gold(I) complexes have also been demonstrated by varying the solvent composition.

Thermodynamic Studies of Cation–Macrocycle Interactions in Nickel Pincer–Crown Ether Complexes Enable Switchable Ligation

The thermochemistry of cation–macrocycle interactions in nickel pincer complexes bearing a hemilabile aza-15-crown-5 or aza-18-crown-6 macrocycle is investigated and applied to cation-controlled reversible ligand binding. Cation–crown interactions were examined in a noncoordinating, low polarity solvent (dichloromethane) and a coordinating, polar solvent (acetonitrile). Structural studies provide solid-state information on cation–crown interactions, whereas binding affinity studies in solution provide quantitative thermodynamic information. The different hemilabile ligand coordination modes have vastly different cation binding affinities, with the tridentate pincer coordination mode binding cations more than 100 000 times more strongly than the tetradentate coordination mode with a crown ether oxygen donating to nickel. Dichloromethane enforces strong cation–crown interactions without disrupting the hemilabile ether ligand, whereas acetonitrile disrupts hemilability by displacing the ethers from the nicke...

Quantitative Collision Cross-Sections from FTICR Linewidth Measurements: Improvements in Theory and Experiment.

Two corrections to the equation used in the cross-sectional areas by Fourier transform ion cyclotron resonance ("CRAFTI") technique are identified. In CRAFTI, ion collision cross-sections are obtained from the pressure-dependent ion linewidths in Fourier transform mass spectra. The effects of these corrections on the accuracy of the cross-sections obtained using the CRAFTI technique are evaluated experimentally using the 20 biogenic amino acids and several crown ether complexes with protonated alkyl monoamines. Good absolute agreement is obtained between the CRAFTI cross-sections and the corresponding cross-sections obtained using both static drift ion mobility spectrometry and computational simulations. These results indicate that the CRAFTI cross-sections obtained using the updated equation presented here are quantitatively descriptive of the size and shape of the gas-phase ions. Cross-sections that differ by less than 3% are measured for the isobaric isomers n-butylamine and tert-butylamine complexed with the crown ethers. This level of precision is similar to what has been achieved previously using traveling wave ion mobility devices. These results indicate that CRAFTI can be used to probe subtle structural differences between ions with approximately the same precision as that achieved in traveling wave ion mobility devices. Graphical Abstract ᅟ.

Synthesis and Structural Characterization of Butadienylcalcium‐based Heavy Grignard Reagents and a Ca4[O] Inverse Crown Ether Complex

AbstractThe structure elucidation of heavy Grignard reagents (RAeX, Ae=Ca, Sr, and Ba, X=halides) has been greatly strived after, mainly because of their inaccessibility and remarkable instability. The synthesis of a series of butadienylcalcium compounds is presented, including 1‐calcio‐4‐lithio‐1,3‐butadiene, 1,4‐dicalcio‐1,3‐butadiene, and a Ca4[O] inverse crown ether complex, via the reaction between 1,4‐dilithio‐1,3‐butadienes and calcium iodide in THF. Single‐crystal X‐ray analysis of these unprecedented heavy Grignard reagents revealed unique structural characteristics and bonding modes. Preliminary reaction chemistry was investigated. This study provides a novel class of alkenyl heavy Grignard reagents and a useful synthetic strategy for otherwise unavailable reactive organometallic compounds.

Synthesis and Structural Characterization of Butadienylcalcium-based Heavy Grignard Reagents and a Ca4 [O] Inverse Crown Ether Complex.

The structure elucidation of heavy Grignard reagents (RAeX, Ae=Ca, Sr, and Ba, X=halides) has been greatly strived after, mainly because of their inaccessibility and remarkable instability. The synthesis of a series of butadienylcalcium compounds is presented, including 1-calcio-4-lithio-1,3-butadiene, 1,4-dicalcio-1,3-butadiene, and a Ca4 [O] inverse crown ether complex, via the reaction between 1,4-dilithio-1,3-butadienes and calcium iodide in THF. Single-crystal X-ray analysis of these unprecedented heavy Grignard reagents revealed unique structural characteristics and bonding modes. Preliminary reaction chemistry was investigated. This study provides a novel class of alkenyl heavy Grignard reagents and a useful synthetic strategy for otherwise unavailable reactive organometallic compounds.

Crown Ether Complexes of Alkali-Metal Chlorides from SO2.

The structures of alkali-metal chloride SO2 solvates (Li-Cs) in conjunction with 12-crown-4 or 1,2-disila-12-crown-4 show strong discrepancies, despite the structural similarity of the ligands. Both types of crown ethers form 1:1 complexes with LiCl to give [Li(1,2-disila-12-crown-4)(SO2 Cl)] (1) and [Li(12-crown-4)Cl]⋅4 SO2 (2). However, 1,2-disila-12-crown-4 proved unable to coordinate cations too large for the cavity diameter, for example, by the formation of sandwich-type complexes. As a result, 12-crown-4 reacts exclusively with the heavier alkali-metal chlorides NaCl, KCl and RbCl. Compounds [Na(12-crown-4)2 ]Cl⋅4 SO2 (3) and [M(12-crown-4)2 (SO2 )]Cl⋅4 SO2 (4: M=K; 5: M=Rb) all showed S-coordination to the chloride ions through four SO2 molecules. Compounds 4 and 5 additionally exhibit the first crystallographically confirmed non-bridging O,O'-coordination mode of SO2 . Unexpectedly, the disila-crown ether supports the dissolution of RbCl and CsCl in the solvent and gives the homoleptic SO2 -solvated alkali-metal chlorides [MCl⋅3 SO2 ] (6: M=Rb; 7: M=Cs), which incorporate bridging μ-O,O'-coordinating moieties and the unprecedented side-on O,O'-coordination mode. All compounds were characterised by single-crystal X-ray diffraction. The crown ether complexes were additionally studied by using NMR spectroscopy, and the presence of SO2 at ambient temperature was revealed by IR spectroscopy of the neat compounds.

Crown ether complex cation ionic liquids: synthesis and catalytic applications for the synthesis of tetrahydro-4H-chromene and 1,4-dihydropyridine derivatives

ABSTRACTA series of crown ether complex cation ionic liquids (CECILs) are synthesized by crown ethers chelated with sodium benzenesulfonates, and used as a green and environmental catalyst, for the synthesis of tetrahydro-4H-chromene and 1,4-dihydropyridine derivatives by three-component reactions of aromatic aldehydes and malononitrile with cyclic β-dicarbonyls or cyclic β-enaminoketones respectively, in H2O/EtOH (1:1), at the reflux condition. CECILs, as a green and environmental catalyst, can be easily obtained and are stable. Furthermore, high conversions, short reaction times, and cleaner reaction profiles are some of the advantages of this method.

Interplay between structure and magnetism in the low-dimensional spin system: K(C8H16O4)2CuCl3·H2O

Materials based on a crown ether complex together with magnetic ions, especially Cu(II), can be used to synthesize new low dimesional quantum spin systems. We have prepared the new crown ether complex Di-\mu-chloro-bis(12-crown-4)-aquqdichloro-copper(II)-potassium, $K(C_8H_{16}O_4)_2CuCl_3{*}H_2O$ (1), determined its structure, and analyzed its magnetic properties. Complex (1) has a monoclinic structure and crystallizes in space group $P2_1/n$ with the lattice parameters of $a=9.5976(5)\r{A}$, $b=11.9814\r{A}, c=21.8713\r{A}$ and $\beta=100.945(4)\deg$. The magnetic properties of this compound have been investigated in the temperature range 1.8 K - 300 K. The magnetic susceptibility shows a maximum at 23 K, but no 3-D long range magnetic order down to 1.8 K. The S=1/2 Cu(II) ions form antiferromagnetically coupled dimers with Cu-Cl distances of $2.2554(8)\r{A}$ and $4.683(6)\r{A}$, and a Cu-Cl-Cu angle of $115.12(2)\deg$ with $2J_{dimer}=-2.96meV (-23.78 cm^{-1})$. The influence of $H_2O$ on the Cl-Cu-Cl exchange path is analyzed. Our results show that the values of the singlet-triplet splitting are increasing considering $H_2O$ molecules in the bridging interaction. This is supported by Density functional theory (DFT) calculations of coupling constants with Perdew and Wang (PWC), Perdew, Burke and Ernzenrhof (PBE) and strongly constrained and appropriately normed (SCAN) exchange-correlation function show excellent agreement for the studied compound.

An in situ formed Ca2+–crown ether complex and its use in CO2-fixation reactions with terminal and internal epoxides

Calcium punched beyond its weight: An in situ formed Ca2+–crown ether complex showed unprecedented efficiency in cyclic carbonate synthesis.

Ring-opening polymerization of rac-lactide catalyzed by crown ether complexes of sodium and potassium iminophenoxides

Crown ether complexes of sodium and potassium iminophenoxides were demonstrated to catalyze the stereoselective polymerization of rac-lactide.

Comment on “Lewis acidic ionic liquids of crown ether complex cations: preparation and applications in organic reactions” by Y. Liang, J. Wang, C. Cheng and H. Jing, RSC Adv., 2016, 6, 93546

In the recently published paper by Liang et al., chlorozincate(ii) anion was identified as [ZnCl3]− based on Raman spectroscopy. According to every textbook and numerous papers, this band corresponds to [ZnCl4]2−.

Crown ether complexes of potassium quinolin-8-olates: synthesis, characterization and catalysis toward the ring-opening polymerization of rac-lactide

Crown ether complexes of potassium quinolin-8-olates were synthesized and demonstrated to catalyze the stereoselective polymerization of rac-lactide.

Half-sandwich lanthanide crown ether complexes with the slow relaxation of magnetization and photoluminescence behaviors.

Four half-sandwich type mononuclear lanthanide crown ether complexes with the formula [Ln(12-crown-4)(NO3)3] (Ln3+ = Dy3+ (1), Tb3+ (2), Ho3+ (3), and Er3+ (4); 12-crown-4 = 1,4,7,10-tetraoxacyclododecane) were successfully synthesized and structurally characterized. Ac magnetic susceptibility measurements reveal that dysprosium complex 1 behaves as a typical single-ion magnet, while solid state photoluminescence studies show that complexes 1 and 2 have the respective lanthanide(iii) luminescence characteristics.

Reply to the ‘Comment’ on “Lewis acidic ionic liquids of crown ether complex cations: preparation and applications in organic reactions” by M. Swadźba-Kwaśny, RSC Adv., 2017, 7, DOI: 10.1039/c7ra05921c

We published recently in RSC Advances a paper, reporting a new group of Lewis acidic ionic liquids that were prepared by the combination of 18-crown-6, alkali metal chloride (NaCl or KCl) and metal chloride (FeCl3, AlCl3, ZnCl2) and applied in organic reactions as catalysts.

Suppressing Cyclic Polymerization for Isoselective Synthesis of High-Molecular-Weight Linear Polylactide Catalyzed by Sodium/Potassium Sulfonamidate Complexes

A new sodium/potassium crown ether complex system with a series of bichelating sulfonamides as ligands was developed for the ring-opening polymerization (ROP) of rac-lactide. In this system, the side reaction of cyclic polymerization can be suppressed very well because of very different ROP rates initiated by BnOH and sulfonamide anion. The synthesis of high molecular weight linear polylactide with molecular weight high up to 107 kg/mol was successful. The best isoselectivity also can reach to a high value of Pm = 0.84. The NMR analysis of the reaction mixture of rac-lactide and complex 3 together with kinetic studies suggests the mechanism of ROP in the absence of alcohol is a coordination–insertion mechanism. After addition of BnOH, the ROP rate can increase remarkably due to the cooperation interaction of alcohol and complex 3.

Insights into the Interaction Energy for Cs+–Crown Ether Complex by Molecular Dynamics Simulations

Cesium is a major fission product in spent nuclear wastes. Crown ethers are used as extracting agent for the removal of cesium ions from aqueous media. We report the interaction energies between the individual complexing species i.e. crown ether and Cs+ metal ion. In order to understand the mechanism of complexation and the behavior of crown ether ligand, crown ether (CE) molecules and Cs+NO3− ions were inserted randomly in the Ionic Liquid-water/methanol biphasic system, where Ionic Liquid is carrier solvent for CE. It was observed that the interaction energies which comprised of the non-bonded interaction during initial stages of the simulation have a value close to zero. This suggests that the Cs+ cation is not present in the crown ether. After the formation of Cs+–CE complex, it is very clear that the electrostatic interactions are particularly attractive in nature and are crucial in realizing complexation.

Accurate Drift Time Determination by Traveling Wave Ion Mobility Spectrometry: The Concept of the Diffusion Calibration.

Ion mobility spectrometry (IMS) is a gas phase separation technique, which relies on differences in collision cross section (CCS) of ions. Ionic clouds of unresolved conformers overlap if the CCS difference is below the instrumental resolution expressed as CCS/ΔCCS. The experimental arrival time distribution (ATD) peak is then a superimposition of the various contributions weighted by their relative intensities. This paper introduces a strategy for accurate drift time determination using traveling wave ion mobility spectrometry (TWIMS) of poorly resolved or unresolved conformers. This method implements through a calibration procedure the link between the peak full width at half-maximum (fwhm) and the drift time of model compounds for wide range of settings for wave heights and velocities. We modified a Gaussian equation, which achieves the deconvolution of ATD peaks where the fwhm is fixed according to our calibration procedure. The new fitting Gaussian equation only depends on two parameters: The apex of the peak (A) and the mean drift time value (μ). The standard deviation parameter (correlated to fwhm) becomes a function of the drift time. This correlation function between μ and fwhm is obtained using the TWIMS calibration procedure which determines the maximum instrumental ion beam diffusion under limited and controlled space charge effect using ionic compounds which are detected as single conformers in the gas phase. This deconvolution process has been used to highlight the presence of poorly resolved conformers of crown ether complexes and peptides leading to more accurate CCS determinations in better agreement with quantum chemistry predictions.

Reversible Stannylenoid Formation from the Corresponding Stannylene and Cesium Fluoride.

A fluorostannylenoid (Cs+ [R2 SnF]- (9), R2 =(TMS)2 CCH2 CH2 C(TMS)2 ) was prepared by reacting a stable dialkylstannylene (R2 Sn (8), R2 =(TMS)2 CCH2 CH2 C(TMS)2 ) with cesium fluoride at room temperature in THF. While 9 is stable in THF and DME, removal of the solvent leads to the regeneration of stannylene 8. No reaction occurred when 8 was treated with CsF in a hydrocarbon solvent. Addition of dibenzo-21-crown-7 ether to the THF solution of stannylenoid 9 followed by usual workup affords the corresponding crystalline stannylenoid crown ether complex, the X-ray structural analysis of which revealed a fluorine-bridged contact ion-pair structure. The reaction of 9 with excess phenylacetylene gives the corresponding di(phenylethynyl)stannane.

Reversible Stannylenoid Formation from the Corresponding Stannylene and Cesium Fluoride

AbstractA fluorostannylenoid (Cs+[R2SnF]− (9), R2=(TMS)2CCH2CH2C(TMS)2) was prepared by reacting a stable dialkylstannylene (R2Sn (8), R2=(TMS)2CCH2CH2C(TMS)2) with cesium fluoride at room temperature in THF. While 9 is stable in THF and DME, removal of the solvent leads to the regeneration of stannylene 8. No reaction occurred when 8 was treated with CsF in a hydrocarbon solvent. Addition of dibenzo‐21‐crown‐7 ether to the THF solution of stannylenoid 9 followed by usual workup affords the corresponding crystalline stannylenoid crown ether complex, the X‐ray structural analysis of which revealed a fluorine‐bridged contact ion‐pair structure. The reaction of 9 with excess phenylacetylene gives the corresponding di(phenylethynyl)stannane.