Binuclear and polynuclear transition metal complexes with macrocyclic ligands. 4. New polydentate azomethine ligands based on 2,5-diformylpyrrole and 2,6-diformylpyridine

The reactions of 2,5-diformylpyrrole (1) and 2,6-diformylpyridine (2) with propane-1,3-diamine afforded new macrocyclic Schiff"s bases 5 and 6, respectively. Their structures were established by NMR spectroscopy and mass spectrometry. Binuclear copper(ii) and nickel(ii) complexes with ligand 5 were synthesized. Pentadentate Schiff"s base, viz., 2,6-bis[(2-aminophenylimino)methyl]pyridine, was prepared by demetallation of its complex with Cd(ClO₄)₂ using Na₂S. In solutions, the latter Schiff"s base is quantitatively transformed into 2,6-bis(benzoimidazolyl)pyridine under the action of atmospheric oxygen or other mild oxidizing agents.     

Binuclear and polynuclear transition metal complexes with macrocyclic ligands. 2. New macrocyclic Schiff"s base in the reaction of 4-tert-butyl-2,6-diformylphenol with 1,2-diaminobenzene. Synthesis and structural,spectroscopic, and theoretical study

Condensation of 4-tert-butyl-2,6-diformylphenol with 1,2-diaminobenzene in ethanol is accompanied by partial reduction of the azomethine double bonds to form symmetrical macrocyclic Schiff"s base containing the alternating >C=N and >CH—NH fragments. In solution, this compound exists as the only isomer in which two endocyclic hydrogen atoms are bound to the oxygen atoms of the phenol groups and two other endocyclic H atoms are attached to the nitrogen atoms of the CH₂—NH fragments. All endocyclic protons are involved in hydrogen bonding and undergo rapid exchange with each other at room temperature. In the crystal, the planar macrocyclic molecules are arranged in closely packed stacks. The steric hindrances resulting from overlapping of the bulky tert-butyl groups are eliminated through rotation of the molecules with respect to each other in the adjacent layers. Study of the potential energy surface for the Schiff"s base under consideration by the DFT method demonstrated that the structure corresponding to the global minimum is similar to that found in solution. However, the isolated molecule is nonplanar, its macrocycle adopting a ladder conformation. The local minimum on the potential energy surface whose energy is 2.6 kcal mol^–1 higher than that of the global minimum corresponds to the zwitterionic structure in which all four endocyclic hydrogen atoms are attached to the nitrogen atoms and the macrocycle adopts a tub conformation. Flattening of the ring is considered as a consequence of stacking interactions between the molecules in the crystal.     

Binuclear and polynuclear transition metal complexes with macrocyclic ligands. 5. Novel complexes of asymmetric polydentate macrocyclic Schiff bases. Step-by-step synthesis

Reactions of 2,6-bis(3-aminopropylaminocarbonyl)pyridine (1) with 4-tert-butyl-2,6-diformylphenol and 2,5-diformylpyrrole in the presence of Ba(ClO₄)₂ in EtOH afford barium complexes with asymmetric macrocyclic Schiff bases as soft and hard ligands. The reaction of compound 1 with Cu(OCOCMe₃)₂ involves closure of a tetrahydropyrimidine ring to give a mononuclear complex, which was structurally characterized by X-ray diffraction analysis.     

Dinuclear and polynuclear transition metal complexes with macrocyclic ligands. 6. New dinuclear copper(ii) complexes with macrocyclic Schiff bases derived from 4-tert-butyl-2,6-diformylphenol

New dinuclear complexes containing Cu^II atoms in the cavity of a macrocyclic Schiff base were prepared by template condensation of 4-tert-butyl-2,6-diformylphenol with 1,3-diaminopropane in the presence of Cu^II trimethylacetate and chloride as well as by extra-ligand exchange. The mononuclear Cu^II complex with two 1,3-diaminopropane molecules can serve as an intermediate in this template synthesis. The reaction of Cu^II trimethylacetate with the unsymmetrical macrocyclic Schiff base synthesized earlier afforded a new dinuclear copper(ii) complex with the amine and imine nitrogen atoms in the coordination sphere. The structures of the new complexes were established by X-ray diffraction analysis and studied by the density functional theory (gradient-corrected PBE functional, TZ2p basis set).     

A new series of dinucleating macrocyclic ligands and their complexes of zinc(II)

A new category of dinucleating macrocyclic Schiff base ligands with ring sizes from 34- to 52-membered have been synthesised employing metal template procedures involving the reaction of o-phenylenediamine with a series of α,ω-bis(3′-hydroxy-4′-formylphenyloxy)alkanes in the presence of calcium(II), barium(II) or manganese(II). The latter cations act as ‘transient’ templates for formation of the corresponding metal-free Schiff base macrocyclic ligands, H₄Lⁿ (where n signifies the number of carbons in each linking bis-alkoxy chain); the macrocycles corresponding to n = 4, 6 and 8 were isolated and characterised while, for n = 1, in which single methylene groups acts as the bridges between salicyl moieties, the cyclic product was used directly for preparation of its dinuclear complex, [Zn₂L¹], without prior isolation. Evidence for the templating role of barium in the preparation of H₄L⁶ and H₄L⁸ was obtained by isolation of the corresponding species of type H₄Lⁿ·2Ba(ClO₄)₂ (n = 6 or 8) as ‘intermediates’ before generation of the respective metal-free macrocycles. Reaction of zinc(II) acetate with the free macrocycles in methanol yielded complexes of type [Zn₂Lⁿ] in all cases. A related non-cyclic ligand, H₂L⁰ and its corresponding mononuclear complex, [ZnL⁰]·H₂O, were also synthesised and its spectral properties compared with those of the macrocyclic derivatives. The elemental analyses, ¹H NMR, IR, UV–Vis and MS spectra of the respective zinc complexes in each case were in accord with the formation of the expected 2:2 condensation product. The results of DFT calculations to probe aspects of the electronic and structural natures of both H₂L¹ and H₄L⁴ are briefly presented.     

New heavy metal ion-selective macrocyclic ligands with mixed-donor atoms and their extractant properties

Synthetic procedures for new macrocyclic diamides with N₂S₄O₃- and N₂S₅O₃-donors were given. The corresponding macrocyclic ligands were prepared by reaction of NaBH₄ with the macrocyclic diamides in the presence of boron triflouride ethyl etherate in dry tetrahydrofuran. The solvent extraction method was used to evaluate metal-ion binding properties of the new ligands. The values of the extraction constants (log K _ex) and the complex compositions were determined for the extracted complexes. The solvent extraction experiments suggested that the reduced N₂S₅O₃-donor macrocycle has Ag⁺ selectivity compared to Pb²⁺, Co²⁺, Ni²⁺, Mn²⁺, and Cd²⁺ for chloroform as organic solvent.     

Crystal structure of the La3+ sandwich complex based on 8-membered macrocyclic siloxanolate ligands

The product of the reaction between anhydrous lanthanum trichloride and potassium vinylsiloxanolate, K₅[VinSiO₂]₈La₄(₄-OH)[O₂SiVin]₈ · 5n-BuOH·2H₂O has been studied by X-ray diffraction. The compound is a «sandwich»-type complex where macrocyclic vinyloctasiloxanolate ligands with regularcis-configuration have co-axial and antiparallel orientation. These ligands coordinate a planar «cationic layer» formed by four La³⁺ ions and stabilized by an additional ₄-OH^– bridge ligand. A three-dimensional cage structure of complex lanthansiloxanolate pentaanions linked through the coordinated K⁺ counter-ions is formed in the crystal studied.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 184–189, January, 1993.     

The synthesis of di- and tetramethyl substituted macrocyclic polyether-diester ligands

Three series of macrocyclic polyether-diester ligands have been prepared from dimethyl triethylene glycol ( 20 ), two dimethyl tetraethylene glycols ( 21,23 ), dimethyl pentaethylene glycol ( 22 ) and tetramethyl tetraethylene glycol ( 24 ) and diglycolyl chloride (products 5–9 ), thiadiglycolyl chloride (products 10–14 ) and 2,6-pyridine dicarbonyl chloride (products 15–19 ). The eighteen-membered rings ( 6 and 16 ) formed solid potassium thiocyanate complexes. The eighteen- and twenty-one-membered ring compounds 6–8 and 16–18 complexed with benzylammonium perchlorate in methylene chloride-d₂ as shown by significant chemical shift changes in the ¹H nmr spectra.     

Electronic, e.p.r., cyclic voltammetric and biological activities of copper(II) complexes with macrocyclic ligands

Eight new macrocyclic ligands have been prepared by the reaction of the precursor diketone (benzil, glyoxal, diacetyl or 2,3-pentanedione) with a diamine (thiosemicarbazide or semicarbazide). Copper(II) complexes of these ligands have been synthesized and characterized by elemental analysis, molar conductance, magnetic susceptibility, i.r., u.v.–vis, ¹H-n.m.r., mass and e.p.r. spectral studies. Mass, n.m.r. and i.r. data indicate the condensation of the diamine and diketone and the whole molecular ion structure. g-Values are calculated for all of the complexes in polycrystalline form as well as in DMSO solution. Spin Hamiltonian values and bonding parameters have also been calculated which indicates that an unpaired electron is present in the orbital. The metal-ligand bonding parameters shows strong in-plane σ sigma and in-plane π bonding. The magnetic and spectral data indicate tetragonal geometry for all of the complexes except [CuH₂L⁴]Cl₂ and [CuH₂L⁴]Cl₂ which are square planar. From c.v. data reversible Cu^II/Cu^I couples are observed for these complexes. The macrocyclic complexes show more antibacterial and antiviral activity as compared to the ligands. The antibacterial activities of the compounds were tested against S. aureus, S. subtillis and E. coli.     

The structure of a potassium-copper complex with six-membered macrocyclic ethylsiloxanolate ligands

The structure of K₂{[EtSiO₂]₆K₂Cu₄[O₂SiEt]₆} · 4n-BuOH, a novel mixed sandwich-like complex of K⁺ and Cu²⁺ with two 6-membered macrocyclic ethylsiloxanolate ligands, was established by means of X-ray study. The ligands have an all-cis configuration and a crown conformation. Four Cu²⁺ and two K⁺ ions form a planar hexagon sandwiched between antiparallel coaxial macrocyclic ligands. The K⁺ ions occupy two opposite apices of the hexagon. The Cu²⁺ ions have square-planar coordination with four siloxanolate O_M atoms, while the K⁺ ions, are coordinated with two O atoms of the solvating butanol molecules, in addition to four O_M atoms. The electric neutrality of the whole complex is due to the two outer-sphere K⁺ counter-ions, each located over one of the two siloxanolate macrocycles, i.e., over the «decks» of the sandwich and coordinated with endocyclic siloxane O_Si atoms, as in crown-ether complexes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 752–756, April, 1993.     

Synthesis and biological activity of Magnesium(II) complexes of heptaaza Schiff base macrocyclic ligands; 1H and 13C chemical shifts computed by the GIAO-DFT and CSGT-DFT methodologies

Two new pendant armed Schiff base macrocyclic complexes, [MgL¹](ClO₄)₂ (1), and [MgL²](ClO₄)₂ (2), have been prepared via cyclocondensation of 2,6-diformylpyridine and 2,6-diacetylpyridine with two hexadentate hexaamines, ten and tmen, in the presence of Mg(II) ion. The ligands are 15-membered pentaaza macrocycles having two 2-aminoethyl pendant arms. The newly prepared complexes are investigated by IR, ¹H NMR, ¹³C{¹H} NMR, DEPT(135), COSY(H, H) and HMQC spectroscopic methods. The antimicrobial screening of newly prepared complexes, 1 and 2, as well as previously prepared similar complexes, [MgL³](ClO₄)₂ (3) and [MgL⁴](ClO₄)₂ (4), against Escherichia coli, Staphylococcus aureus and candidia albicans showed that the macrocyclic complexes of Mg(II) containing 15-membered pentaaza ring (1, 2 and 3) have no activity. Where as the compound 4, which contain 16-membered pentaaza ring, had remarkable inhibition zone on the culture of S. aureus and E. coli as compared with standard drugs. The ¹H and ¹³C chemical shieldings of gas phase complexes were also studied by the gauge independent atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) methods at the level of density functional theory (DFT). The computed ¹³C chemical shifts are in reasonably good agreement with the experimental data.     

Synthesis, characterization and crystal structures of di-three-coordinated copper(I) macrocyclic Schiff base complexes

The air-stable di-copper(I) complexes Cu₂L(SCN)₂ (1) and Cu₂L(SCN)_1.86I_0.14 (2) of the N₄ macrocyclic Schiff base ligand L have been synthesized and characterized by IR, elemental analysis, UV-Vis and crystal structure determination. X-ray analysis of the complexes shows an approximate distorted trigonal planar geometry around each copper(I) ion that is constructed from one N-bonded thiocyanate (or iodide in 2) group and two imine nitrogen atoms. DFT calculations were used to determine the structural features of the Cu₂L(SCN)₂ complex, and these were consistent with the experimental data for the complex.     

Encapsulation of Pd(II) by N4 and N2O2 macrocyclic ligands: their use in catalysis and biology

New macrocyclic Schiff base Pd(II) compounds were synthesized by treating N₄ and N₂O₂ macrocycles with palladium chloride in a 1 : 1 ratio. The resulting macrocyclic compounds were characterized by elemental, IR, ¹H-NMR, ¹³C-NMR, mass, molar conductance, magnetic susceptibility, electronic spectra, and thermal analysis. These compounds were used as catalysts in the development of an efficient catalytic method for reduction of organic substrates having nitro, olefinic, acetylenic, and aldehyde groups under mild reaction conditions. The biological activities of all the macrocycles and macrocyclic Pd(II) compounds have been tested against gram positive (Bacillus subtilis and Staphylococcus aureus) and gram negative (Escherichia coli and Klebsiella pneumonia) bacteria and found to be more active than commercially available antibacterial drugs like Streptomycin and Ampicillin.     

Pyrrole macrocyclic ligands for Cu-catalyzed asymmetric Henry reactions

New chiral perazamacrocycles containing four pyrrole rings have been synthesized by the [2+2] condensation of (R,R)-diaminocyclohexane and 5,5'-(alkane-2,2-diyl)bis(1H-pyrrole-2-carbaldehydes). These macrocycles, differing for the alkyl/aryl meso-substituents, were used as ligands in the copper-catalyzed Henry reactions of aromatic and aliphatic aldehydes with nitroalkanes. In the optimized experimental conditions, the condensations of nitromethane and aromatic and aliphatic aldehydes in the presence of catalytic amounts of copper diacetate and methyl-substituted macrocyclic ligand (2:1 ratio) in ethanol at room temperature provided products often with high enantiomeric excesses (up to 95% ee). The positive influence of the macrocyclic structure on the efficiency/enantioselectivity of the catalytic system was demonstrated by comparison with the outcomes of Henry reactions performed using analogous macrocyclic ligands (trianglamines) and open-chain ligands derived from (R,R)-diaminocyclohexane.     

Binuclear and polynuclear transition metal complexes with macrocyclic ligands 7. Directed step-by-step synthesis of novel unsymmetric macrocyclic ligands

Novel asymmetric macrocyclic Schiff bases were synthesized by the condensation of N,N′-bis(2-aminophenyl)-3,4-diphenylthiophene-2,5-dicarboxamide (1) with diformyl derivatives of phenol, furan, difurans, pyridine, pyrrole, and dipyrroles. The reaction proceeds in high yields and without by-products in methanol in the presence of inorganic and organic acids (proton-template condensation). In the case of monocyclic diformyl derivatives and di(5-formylfuran-2-yl) sulfide, the reaction occurs in 1,4-dioxane (templateless synthesis). The synthesized macrocycles were characterized by elemental analysis data and NMR and mass spectra. For Part 6, see Ref. 1. Dedicated to Academician N. S. Zefirov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2152–2156, September, 2005.     

Synthesis and characterization of two new macrobicyclic salts containing hexahydropyrimidine moieties: experimental and density functional theory studies

Two macrocyclic Schiff base ligands (L¹, L²) and their related reduced forms (L³ and L⁴) have been prepared. In the presence of nickel(II) perchlorate in methanol, the reinforced macrobicyclic salts containing hexahydropyrimidine cation moiety have been developed. Here, it seems that Ni(II) perchlorate acts as oxidizing agent converting methanol to the formaldehyde which in turn bridges two nitrogen atoms of reduced forms of macrocycle producing final products. All Schiff base ligands and their reduced forms together with related salts were characterized by elemental analysis, IR spectroscopy, ¹H and ¹³C NMR, EI-Mass and in the case of [L^3′](ClO₄) salt by X-ray crystallography. The proposed mechanism for the formation of macrobicyclic ligand [L^3′] from the reaction of macrocyclic ligand L³ and formaldehyde has also been studied via density functional theory (DFT).     

Synthesis of four novel pendant armed macrocyclic ligands and their interaction with lanthanide(III) cations

The ability of La³⁺ ions to form stable complexes with four novel pendant-armed N_xO_y-macrocycles derived from 2,6-bis(2-formylphenoxymethyl)pyridine, L¹, L², L³, and L⁴, has been studied. The corresponding (unsubstituted) parent ligands were prepared by the reaction between 2,6-bis(2-formylphenoxymethyl)pyridine and three different amines: 1,2-bis(2-aminophenoxy)propane (L¹), diethylenetriamine (L²), and 3,6-dioxa-1,8-octanediamine (L³ and L⁴). This was followed for the parent ligands of L¹, L³, and L⁴ by in situ reduction with sodium borohydride. The pendant-armed ligands were then synthesized by the alkylation of the free-NH groups with p-(L¹ and L³) and o-nitrobenzyl bromide (L⁴), and 2-chloromethylpyridine chlorohydrate (L²). A series of Ln(III) complexes were prepared for the four ligands by the direct synthesis between the corresponding macrocycle and Ln(III) hydrated nitrates and perchlorates. The number of complexes obtained from the pendant-armed macrocycles is lower than that of the (unsubstituted) parent ones, suggesting that the introduction of pendant arms in the macrocyclic skeletons increases the selectivity of the ligands. More complexes were synthesized when using nitrate as the counterion, showing the important role of the counterion in the complexation reaction. The text was submitted by the authors in English.     

Dinuclear macrocyclic palladium complexes having pincer coordinating groups and their catalytic properties in Mizoroki-Heck reactions

An improved synthetic method of palladium(II) dinuclear macrocyclic complexes have been described. Each of the two isomers of the complexes [Pd₂LBr₂] has a macrocyclic ligand L in which two 2,6-bis(diaminomethyl)phenyl units coordinate to the Pd(II) centers with N, C, N donor atoms. Substitution of the bromo ligands of one of the isomer of the complexes with acetonitrile ligands affords a new dinuclear complex. Catalytic activities of these complexes were studied for the Mizoroki-Heck type reactions of iodobenzene and styrene. High turnover number up to 30,000 was achieved using one of the isomer of the complexes.     

新型含芳基 恶二唑带支臂大环多胺和磊环聚醚的 合成研究

利用稀释法合成了五个不同结构类型的芳基恶二唑类大环多胺和大环聚醚,并研究了它们对金属离子的络合作用。     

Synthesis, crystal structures and DNA-binding properties of dinuclear complexes with macrocyclic ligands

Two symmetrical macrocyclic dinuclear complexes, [Cu₂L¹(ClO₄)₂(H₂O)₂][Cu₂L¹(H₂O)₂] (ClO₄)₂ (1) and [Cu₂L²(ClO₄)₂] (2), (where H₂L¹ and H₂L² are the [2?+?2] condensation products of 1,3-diaminopropane with 2,6-diformyl-4-methylphenol and 2,6-diformyl-4-flurophenol, respectively), have been synthesized and characterized. The electronic and magnetic properties of the complexes were studied by cyclic voltammetry and magnetic susceptibility. There are strong antiferromagnetic couplings between the two copper(II) centers in both complexes. The strongly electron-withdrawing fluorine groups in H₂L² weaken the antiferromagnetic exchange, but make the metal centers more easily reduced than its analog H₂L¹. The interactions of the complexes with calf thymus DNA were studied by UV?CVis and CD spectroscopic techniques.