Macrocyclic Tetra Research Articles

Macrocyclic luminophores under confinement in a polymeric matrix – induction of large-Stokes shift by inter-unit proton transfer

Macrocyclic tetra(naphthimidazole)resorcin[4]arenes exhibit large Stokes shifts upon embedding in PMMA matrix enabling their applications in luminescent solar concentrator technology.

Macrocyclic tetra(azo-) and tetra(azoxyfurazan)s: Comparative study of decomposition and combustion with linear analogs

Thermal decomposition and combustion of macrocyclic tetra(azofurazan), TATF, and tetra(azoxyfurazan), TOATF, were studied using a number of complementary experimental techniques, namely thermogravimetry, differential scanning calorimetry, manometry, microthermocouple measurements in a combustion wave. Kinetic studies of polyazo- and azoxyfurazans have demonstrated that macrocycles, TATF and TOATF, have a different mechanism of thermal decomposition than their linear counterparts. While linear azo- and azoxyfurazans have relatively low activation energy (130–143 ​kJ·mol−1) of thermal decomposition, the activation energies for macrocyclic TATF and TOATF are 202–210 ​kJ·mol−1, which is close to the calculated breaking energy of the C-NN bond. The initial stage of decomposition of these macrocycles is the monomolecular cleavage of the C-NN bond, while linear azofurazan decomposes according to a concerted mechanism, loss N2 or N2O molecules. It was found that the condensed-phase chemistry determines the combustion mechanism of TOATF. Combustion instability is observed for TATF in the pressure range below 3 ​MPa. Both macrocyclic TATF and TOATF are relatively fast-burning energetic compounds, with burning rates exceeding the burning rates of the CL-20.

Structural Versatility and Supramolecular Isomerism in Redox‐Active Tetra‐ and Hexaruthenium Macrocycles

We report on six macrocyclic tetra‐ and hexaruthenium complexes formed by the self‐assembly of 2,5‐divinylthiophene‐ or 2,5‐divinylfuran‐bridged diruthenium and 2,5‐thiophene‐, ‐furan‐ or ‐pyrroledicarboxylate linkers. All complexes were scrutinized by NMR spectroscopy and UHR ESI‐MS, cyclic and square wave voltammetry and, in five cases, by X‐ray diffraction analyses. Although the utilized building blocks differ only slightly with respect to their intrinsic bite angles, the resulting macrocycles exhibit remarkable structural versatility. Electrolysis inside an optically transparent electrochemical (OTTLE) cell provided their associated di‐/tri‐ and tetra‐/hexacations, which were studied by IR, UV/Vis/NIR and EPR spectroscopy. The divinylthiophene‐furandicarboxylate complex 2‐TF provides a rare example of supramolecular isomerism in metallamacrocyclic complexes. Thus, hexanuclear 2‐TF6 is initially formed as a kinetic isomer, which subsequently transforms slowly and cleanly into tetranuclear 2‐TF4.

Electronic Finetuning of a Bio-inspired Iron(II) tetra-NHC Complex by trans Axial Isocyanide Substitution.

The synthesis of trans axially substituted mono‐ (1 a) and bis(tert‐butylisocyanide) (1 b) derivatives of the highly active homogeneous bio‐inspired iron(II) olefin epoxidation (pre‐)catalyst 1 bearing an equatorial macrocyclic tetra N‐heterocyclic carbene and two trans axial labile acetonitrile ligands is reported. NMR spectroscopy and SC‐XRD indicate a considerable π‐backdonation from the iron(II) centres to the isocyanide ligand(s). The impact of isocyanide substitution on the electronic features of the complexes is studied by cyclic voltammetry revealing a significant increase in half‐cell potential assignable to the reversible Fe(II)/Fe(III) redox couple with an increasing number of isocyanides as a result of their π‐accepting properties: E1/2=0.15 V (1), E1/2=0.35 V (1 a), E1/2=0.44 V (1 b).

A macrocyclic silver polycarbene complex based on 1,2,4-triazole units: synthesis and postsynthetic modification.

Facile synthesis and postsynthetic modification of a rectangular 1,2,4-triazole-based NHC macrocycle have been developed. The silver complex [Ag2(1)2](BF4)2 is derived from the corresponding triazole salt H2-1(BF4)2 upon reaction with Ag2O. The structure of the metallocyclic Ag-NHC complex [Ag2(1)2](BF4)2 was determined by single-crystal X-ray diffraction analysis. The metal-carbene template undergoes photodimerisation of its terminal cinnamic esters (UV irradiation, λ = 365 nm) and generates a macrocyclic tetra (NHC) ligand. The desired tetra-1,2,4-triazole macrocycle was isolated in good yield by eliminating the metal ions from the photodimerisation product. All complexes were fully characterized by multinuclear NMR measurements (1H, 13C{1H}, COSY, HSQC and HMBC) and ESI mass spectroscopy.

Ga–Ga Bonds as Key Building Blocks for the Formation of Supramolecular Entities – Unusual Macrocyclic Tetra‐ and Octagallium Compounds

Treatment of the digallium compound R2Ga–GaR2 (1) [R = CH(SiMe3)2] with the dicarboxylic acids 1,2‐ and 1,4‐(HO2CCH2O)2C6H4 afforded, by the release of H2C(SiMe3)2, macrocyclic compounds 2a and 2c, in which two organic spacer ligands connect two metal–metal bonds. Two CO2 groups bridge each Ga–Ga bond, and different structures resulted with a parallel or perpendicular arrangement of the bridging ligands. The resorcinol derivative 1,3‐(HO2CCH2O)2C6H4 yielded the unique compound 2b, in which four Ga–Ga bonds are bridged by four spacer ligands. The organic groups form loops, which are alternately arranged above and below the molecular plane with four saddle points and a structure approaching 4 symmetry. The 1,2‐ and 1,4‐diacids afforded tetrakis(digallium) compounds 3a and 3c in the presence of water. In both cases carboxylate groups and hydroxido ligands bridge two Ga atoms of two different Ga–Ga bonds. The spacer ligands connect two of these fragments and adopt parallel orientations to form molecular boxes. Again, the 1,3‐diacid afforded a unique structural motif in which a Ga4O6 skeleton (two Ga–Ga bonds) is bridged by a single organic spacer, reminiscent of the handle of a basket.

Reversible photochemical modifications in dicarbene-derived metallacycles with coumarin pendants.

Molecular rectangles were obtained from two bis(NHC) ligands, each featuring two terminal coumarin groups and two Ag(+), Au(+), or Cu(+) ions. Upon UV irradiation (λ=365 nm), the dinuclear complexes undergo photochemical modification through a [2+2] cycloaddition reaction of two adjacent coumarin moieties to give a macrocyclic tetra(NHC) ligand. The photodimerization of the coumarin pendants proceeds stereoselectively to give the syn-head-head isomers in all cases. Subsequent irradiation at λ=254 nm initiates a photocleavage reaction with reconstitution of the initial dinuclear complexes with coumarin pendants.

ChemInform Abstract: New Hexaaza Macrocyclic Binucleating Ligands. Oxygen Insertion with a Dicopper(I) Schiff Base Macrocyclic Complex.

Direct 2:2 condensation of isophthalaldehyde with diethylenetriamine produces a hexaaza 24-membered macrocyclic tetra Schiff base in good yield. The crystal structure of an isomeric form of the Schiff base is reported. The amber binuclear Cu(I) complex of the tetraaza macrocyclic Schiff base combines with a molar equivalent of dioxygen to form a green binuclear Cu(II) complex, wich contains a bridging hydroxide ion and, by oxygen insertion, a bridging phenolate donor

Convenient Enantioselective Hydrosilylation of Ketones Catalyzed by Zinc‐Macrocyclic Oligoamine Complexes

Abstractmagnified imageChiral macrocyclic tetra‐ and hexamine macrocycles derived from trans‐1,2‐diaminocyclohexane (DACH) in complexes with diethylzinc efficiently catalyze the asymmetric hydrosilylation of aryl alkyl ketones with enantiomeric excess of the product up to 89%. The cyclic structure of the trianglamine ligand increases the enantioselectivity of the reaction, in comparison to the catalysis with the acyclic N,N′‐dibenzyl‐DACH ligand. Density functional theory (DFT) computations on the structures of ligand‐zinc complexes and on the structures of these complexes with a coordinated acetophenone molecule allow us to rationalize the direction of the asymmetric induction of the hydrosilylation reaction as well as the superiority of the cyclic ligand compared to the acyclic one. This is the first example of asymmetric catalysis for the hydrosilylation reaction of ketones with the use of a readily available, inexpensive, and reusable macrocyclic trianglamine ligand.

New Synthons for the Synthesis of Lanthanide Containing Macrocyclic Schiff Bases Featuring Substituents Available for Tethering

2,6-Diacetylpyridine substituted with amine or alcohol groups in the 4-position have been prepared from chelidamic acid. The key 4-chloro derivative was synthesized in high yield via a diazo intermediate and was protected as a bis-1,3-dioxane before substitution with various amino alcohol groups. Lanthanide macrocyclic tetra–imine complexes were obtained by a template procedure that leads to stable paramagnetic and/or fluorescent derivatives with anchor groups available for linkage to macromolecules.

Chiroptical features and luminescence behaviour of macrocyclic tetra(4-quinolyl)-complexes: surprising absence of exciton coupling

The C4-symmetric (S)-tetra(4-quinolyl) tetraamide derivative of dota has been prepared. The sodium complex has been characterised by X-ray crystallography and although the quinolyl groups are appropriately oriented for exciton coupling in the solid-state, in solution no evidence for coupling was found for the free ligand nor its protonated, Na, Ca or Eu complexes. Instead, excimer formation was observed in emission consistent with a coplanar arrangement of the quinolyl groups.

Synthesis and X-ray Crystal Structures of a Calixarene-Related, Tetraamino, Tetraphenolic, Polynucleating Macrocyclic Ligand and Its ZnII4 and CoIII3 Derivatives

Reduction with NaBH 4 of the macrocyclic tetra Schiff base ligand formed by condensation of two molecules of 2,6-diformyl-4-methylphenol with two molecules of 2,6-bis(aminomethyl)-4-methylphenol affords the corresponding tetraamino, tetraphenolic macrocyclic ligand L r H 4 . Determination of the structure of the hydrochloride salt with the remarkable solvation composition L r H 4 .4HCl.H 2 O.CH 3 OH.C 2 H 5 OH, reveals a dome-shaped L r H 8 4+ cation with a water molecule and two of the chloride ions H-bonded inside the domed macrocyclic cavity

Synthesis, x-ray crystal structures, and magnetic properties of tetranickel complexes of a macrocyclic tetranucleating ligand

Replacement of the acetato ligands in the previously reported LNi 4 (OH)(CH 3 O.H.OCH 3 )(CH 3 CO 2 ) 2 (where LH 4 is the macrocyclic tetra Schiff base formed by condensation of two molecules of 2,6-diformyl-4-methylphenol with two molecules of 2,6-bis(aminomethyl)-4-methylphenol) either by azide or by methoxide gives derivatives which, X-ray studies reveal, contain the intact [LNi 4 (OH)(CH 3 O.H.OCH 3 )] 3+ core present in the acetato complex

Biomimetic ion transport: Synthesis and activity of an amphotericin mimic

A bolaform amphiphile derived from two macrocyclic tetra ester units was prepared as a mimic of the pore-forming antibiotic amphotericin. The mimic mediates collapse of cation and pH gradients across vesicle bilayer membranes.

ChemInform Abstract: Synthesis and X‐Ray Crystal Structures of Ni4 and Zn4 Complexes of a Macrocyclic Tetranucleating Ligand.

AbstractThe tetranuclear complexes (I) and (II) of the macrocyclic tetra Schiff base formed by condensation of two molecules of 2,6‐diformyl‐4‐methylphenol with two molecules of 2,6‐bis(aminomethyl)‐4‐methylphenol in the presence of Ni(II) or Zn(II) acetate, sodium acetate and acetic acid (for (II) yield given in g).

Incipient pentagonal-pyramidal coordination of tellurium in a macrocyclic tetra(secondary amine) complex

[(C 8 H 16 N 4 H 3 ) 2 Te 2 O 2 ]Cl 2 •4CHCl 3 •2CH 3 OH cristallise dans le systeme monoclinique avec le groupe d'espace P2 1 /c. Affinement de la structure jusqu'a 0,080

Preparation of a novel sulfur-nitrogen cage compound by the transamination of bis(dimethylamino) sulfide with a macrocyclic tetra(secondary amine)

Reaction du bis-dimethylamino sulfure avec le tetra-aza-1,4,7,10cyclododecane (A): obtention du derive diepithio-1,7:4,10 de A; etude RX