Binuclear and polynuclear transition metal complexes with macrocyclic ligands. 3. New polydentate macrocyclic ligands in reactions of 4-alkyl-2,6-diformylphenols with 1,2-diaminobenzenes

The mechanism of abnormal condensation of 2,6-diformyl-4-R-phenols with 1,2-diaminobenzenes accompanied by the reduction of two of four double C=N bonds in macrocyclic Schiff"s bases formed was studied by DFT (gradient-corrected PBE functional, TZ2p basis set). In the first step, [1+1] Schiff"s base is formed and disproportionates further to afford amine and benzoimidazolylphenols. Two new macrocyclic polydentate ligands containing two CH₂—NH moieties in the rings were synthesized. The reduction of one of these ligands with sodium borohydride gave the new macrocyclic ligand, whose structure and conformations were studied by the DFT method.     

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.     

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).     

Binuclear and polynuclear transition metal complexes with macrocyclic ligands 1. Synthesis and the structure of an antiferromagnetic binuclear nickel complex prepared by the reaction of o-phenylenediamine with pyrrole-2,5-dicarbaldehyde and nickel pivalate

The reaction of pyrrole-2,5-dicarbaldehyde (1) with o-phenylenediamine (2) in anhydrous EtOH afforded a [1+1]-condensation product, viz., Schiff"s base. The structure of the latter was established by NMR spectroscopy and X-ray diffraction analysis. The reaction of this product or a mixture of 1 and 2 with Ni₉(_n-OOCBu^t)₁₂(HOOCBu^t)₄(₄-OH)₃(₃-OH)₃ in MeCN in the presence of AcOH gave rise to an antiferromagnetic binuclear complex. According to the X-ray diffraction data, the macrocycle in the latter complex is a [2+2]-condensation product of compounds 1 and 2, _eff ranging from 0.569 to 2.614 B (2—301 K), –2J = 360 cm^–1. The Ni₂(OAc)₂ fragment is located in the central cavity of the macrocycle. The structures of the condensation products are discussed based on the results of DFT quantum-chemical calculations.     

Synthesis,spectroscopic, thermal analyses,biological activity and molecular docking studies on mixed ligand complexes derived from Schiff base ligands and 2,6‐pyridine dicarboxylic acid

Two novel Schiff base ligands (L^a and L^b) were prepared from the condensation of quinoline 2‐aldehyde with 2‐aminopyridine (ligand L^a) and from the condensation of oxamide with furfural (ligand L^b). Mixed ligand complexes of the type M⁺²L^a/b L^c were prepared, where (L^a and L^b) the primary ligands and L^c was 2,6‐pyridinedicarboxylic acid as secondary ligand. Metal ions used were Fe(II), Co(II), Ni(II) and Zn(II) for mixed ligands L^a L^c and Fe(II), Co(II), Ni(II), Cu(II), Hg(II) and Zn(II) for L^bL^c mixed ligands. L^a and L^b Schiff base ligands were both characterized using elemental analyses, molar conductance, IR, ¹H and ¹³C NMR. Mass spectra for L^b, [Zn(L^a)L^cCl]Cl and [Cu(L^b)L^cCl]Cl were also studied. ESR spectrum of the [Cu(L^b) L^cCl]Cl complex was also recorded The metal complexes were synthesized and characterized using elemental analyses, spectroscopic (IR, ¹H NMR, UV‐visible, diffused reflectance), molar conductance, magnetic moment and thermal studies. The IR and ¹H NMR spectral data revealed that 2,6‐pyridinedicarboxalic acid ligand coordinated to the metal ions via pyridyl N and carboxylate O without proton displacement. In addition, the IR data showed that L^a and L^b ligands behaved as neutral bidentate ligands with N₂ donation sites (quinoline N and azomethine N for L^a and two azomethine N for L^b). Based on spectroscopic studies, an octahedral geometry was proposed for the complexes. The thermal stability and degradation of the metal complexes were investigated by thermogravimetric analysis. The binding modes and affinities of L^a, L^b and Zn(II) complexes towards receptors of crystal structure of E. coli (PDB ID: 3 t88) and mutant oxidoreductase of breast cancer (PDB ID: 3 hb5) receptors were also studied. The antimicrobial activity against two species of Gram positive, Gram negative bacteria and fungi were tested for the Schiff base ligands, 2,6‐pyridinedicarboxylic acid and the mixed ligand complexes and revealed that the synthesized mixed ligand complexes exhibited higher antimicrobial activity than their free Schiff base ligands.     

New polydentate macrocyclic ligands of hybrid amine-imine and amide-imine types as artificial anion receptors. Synthesis and study of anion binding

Three new macrocyclic Schiff bases containing an amine or amide structural fragment along with imine groups were synthesized by condensation of 2,6-bis(2-aminophenyliminomethyl)pyridine (1) and N, N’-bis(2-aminophenyl)pyridine-2,6-dicarboxamide (2) with 2,5-diformylpyrrole (₃) and 2,2-bis(5-formylpyrrol-2-yl)propane (4). The reaction of compound 1 with 3 proceeds abnormally and is accompanied by redox disproportionation of compound 1 in the first step. The structure of the macrocyclic product of this reaction was established by X-ray diffraction analysis. Spectrophotometric titration showed that hybrid macrocycle 10, which was prepared by condensation of compound 2 with 4, possesses the properties of an anion receptor and selectively binds hydrosulfate and dihydrophosphate anions in the presence of bromide and nitrate anions. The structures of 10 and its adduct with the hydrosulfate anion were calculated by density functional theory.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 161–168, January, 2005.     

Covalent nano-clip and nano-box compounds based on free base porphyrins

Novel nano-clip and nano-box compounds were obtained by reaction between dibromomethane and 5,15-di[p-(9-methoxytriethylenenoxy)phenyl]-10,20-di[p-hydroxyphenyl]porphyrin. The molecular architecture varies from a co-facial (nano-clip) to a four wall-box (nano-box) structure. The products were characterized by ¹H NMR and UV-vis spectroscopy and MALDI-TOF mass spectrometric analysis.The UV-vis spectra of the nano-clip showed a modification of the characteristic porphyrin soret and Q bands, with respect to the monomer and cyclic tetramer, as a probable consequence of a hybrid orbital deformation (HOD) phenomenon involving the two porphyrin π rings forced to a closer co-facial spatial arrangement. The spatial distance between the two co-facial porphyrin units, and therefore the molecular cavity size, can be modified inducing an electrostatic repulsion by means of a reversible protonation of the pyrrolic cores. The ¹H NMR spectra of the nano-box showed a strong high-field shift of some aromatic and ether protons present in the upper and lower rim of the molecular box.     

Synthesis and properties of nickel(ii) diiminodithiolate and diiminodisulfide N2S2-type complexes. New complexes with non-innocent ligands

The following two groups of nickel(ii) diiminodithiolate and diiminodisulfide N₂S₂-complexes were synthesized for the first time: (1) complexes with complete conjugation between all four donor centers, viz., compounds with non-innocent ligands, and (2) complexes containing a short conjugation system involving only two imino groups of the ligand. The complexes were studied by ¹H NMR, ESR, and UV spectroscopy, mass spectrometry, and electrochemistry. Solutions of glyoxal bis(2-mercaptoanil)nickel(ii) in DMF showed an ESR signal, which decreased with time, the processes being accompanied by an analogous change in the intensity of the absorption band at 931 nm. The electrochemical properties of this complex also change with time. The results of studies demonstrated that compounds with non-innocent ligands of this type were initially generated as classical diiminodithiolate structures, which were transformed into the ortho-iminothiosemiquinonate biradicals and then into oligomeric complexes both in solution (fast transformation) and in the solid state (slow transformation). Oligomeric structures of these compounds are stable for a long period of time.     

New d heterometallic coordination polymers based on compartmental Schiff-base ligands. Synthesis, structure and luminescence

The self-assembly processes between binuclear [Zn₂Lⁿ]²⁺ complex cations and complex anions, [M(CN)₂]⁻ [M(I) = Ag(I), Au(I)], generate new one-dimensional (1-D) coordination polymers: ¹_∞[{L¹Zn₂(μ₃-OH)}₂(H₂O){μ-[Ag(CN)₂]}](ClO₄)₃ THF 0.5MeOH 1, ¹_∞[{L¹Zn₂(μ₃-OH)}₂(H₂O){μ-[Au(CN)₂]}](ClO₄)₃ THF H₂O 2, ¹_∞[{L²Zn₂(μ-OH)}{μ-[Ag(CN)₂]}][Ag(CN)₂] H₂O 3 (H₂Lⁿ are bicompartmental Schiff-base ligands resulting from condensation reactions between 2,6-diformyl-p-cresol with 2-aminomethyl-pyridine, and 2-aminoethyl-pyridine, respectively). The luminescence properties of the new heterometallic complexes have been investigated.     

Carbenoid reactions of trifluoromethylelement compounds. Part 4. Reactions of trifluoromethylzinc bromide with enamines and methylene bases

The reactions of ZnBr(CF₃)·2CH₃CN with 1-morpholinocyclo-pentene and -hexene have been investigated and found to yield mixtures of two isomers of 1-morpholino-1-cyanomethyl-2-difluoromethyl-cyclopentane and -hexane, respectively. The interaction with methylene bases of nitrogen heterocycles leads to the formation of trimethinecyanine dyes. This reaction sequence includes the formation of two carbon-carbon bonds in a one-pot operation. The mechanism of the reactions is discussed.     

Transition metal bisdithiolene complexes based on extended ligands with fused tetrathiafulvalene and thiophene moieties: new single-component molecular metals

The gold and nickel bisdithiolene complexes based on new highly extended ligands incorporating fused tetrathiafulvalene and thiophene moieties (alpha-tdt=thiophenetetrathiafulvalenedithiolate and dtdt=dihydro- thiophenetetrathiafulvalenedithiolate), were prepared and characterised by using cyclic voltammetry, single crystal X-ray diffraction, EPR, magnetic susceptibility and electrical transport measurements. These complexes, initially obtained under anaerobic conditions as diamagnetic gold monoanic [nBu(4)N][Au(alpha-tdt)(2)] (4), [nBu(4)N][Au(dtdt)(2)] (3) and nickel dianionic species [(nBu(4)N)(2)][Ni(alpha-tdt)(2)] (8), [(nBu(4)N)(2)][Ni(dtdt)(2)] (7), can be easily oxidised to the stable neutral state just by air or iodine exposure. The monoanionic complexes crystallise in at least two polymorphs, all of which have good cation and anion segregation in alternated layers, the anion layers making a dense 2D network of short SS contacts. All of the neutral complexes, obtained as microcrystalline or quasi amorphous fine powder, present relatively large magnetic susceptibilities that correspond to effective magnetic moments in the range 1-3 mu(B) indicative of high spin states and very high electrical conductivity that in case of the Ni compound can reach sigma(RT) approximately 250 S cm(-1) with a clear metallic behaviour. These compounds are new examples of the still rare single-component molecular metals.     

Four‐, five‐ and six‐coordinated transition metal complexes based on naphthalimide Schiff base ligands: Synthesis,crystal structure and properties

Two bidentate Schiff base ligands (HL¹ = N‐n‐butyl‐4‐[(E)‐2‐(((2‐aminoethyl)imino)methyl)phenol]‐1,8‐naphthalimide; and HL² = N‐n‐butyl‐4‐[(E)‐2‐(((2‐aminoethyl)imino)methyl)‐6‐methoxyphenol]‐1,8‐naphthalimide) with their metal complexes [Cu(L¹)₂] ( 1 ), [Zn(L¹)₂(Py)]₂?H₂O ( 2 ) and [Ni(L²)₂(DMF)₂] ( 3 ) have been synthesized and characterized. Single‐crystal X‐ray structure analysis reveals that complex 1 has a four‐coordinated square geometry, while complex 2 is a five‐coordinated square pyramidal structure and complex 3 is a distorted six‐coordinated octahedral structure. Cyclic voltammograms of 1 indicate an irreversible Cu²⁺/Cu⁺ couple. In vitro antioxidant activity assay demonstrates that the ligands and the two complexes 1 and 3 display high scavenging activity against hydroxyl (HO^?) and superoxide (O₂^??) radicals. Moreover, the fluorescence properties of the ligands and complexes 1 – 3 were studied in the solid state. Metal‐mediated enhancement is observed in 2 , whereas metal‐mediated fluorescence quenching occurs with 1 and 3 .     

Synthesis and spectroscopic study of the d-metal complexes with new octa(benzo-15-crown-5)-substituted phthalocyanine

Octa(benzo-15-crown-5)-substituted phthalocyanine and its complexes with d-metals (Ni^II, Co^II, Cu^II, Zn^II, and Cd^II) have been synthesized for the first time. The compounds were studied by UV—Vis spectroscopy, MALDI-TOF mass spectrometry, NMR, ESR, IR spectroscopy, and Raman spectroscopy. The dependence of the spectral characteristics of the studied compounds on the ion radius of the complexing agent was demonstrated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1439–1447, July, 2008.     

Studies on mononuclear chelates derived from substituted Schiff-base ligands (Part 10): synthesis and characterization of a new 4-hydroxysalicyliden- p -aminoacetophenoneoxime and its complexes with Co(II), Ni(II), Cu(II) and Zn(II)

In this study, 4-hydroxysalicylaldehyde-p-aminoacetophenoneoxime (LH) was synthesized starting from p-aminoacetophenoneoxime and 4-hydroxysalicylaldehyde. Complexes of this ligand with Co(II), Ni(II), Cu(II) and Zn(II) were prepared with a metal?: ligand ratio of 1?:?2. The ligand and its metal complexes have been characterized by elemental analyses, IR, ¹H- and ¹³C-NMR spectra, magnetic susceptibility measurements and thermogravimetric analyses (TGA).     

Synthesis and properties of new poly(ether-ester)s containing aliphatic diol based on isosorbide. Effects of the microwave-assisted polycondensation

Microwave irradiation was applied to synthesize to the bulk synthesis of novel poly(ether-ester)s based on diol-ether of isosorbide (1) and adipoyl chloride (2) or terephthaloyl chloride (3). Thus, the poly(ether-ester)s (4 and 5) consist partially of isosorbide. In order to check the influence of microwaves and possible specific non-thermal microwave effects, the reactions were comparatively performed inside a thermostated oil bath under similar conditions. The reaction conditions were varied to optimize both yields and molecular weights of poly(ether-ester)s. The reaction proceeded roughly five times faster under microwave irradiation, the polycondensation being almost completed (yields upto approximately 95%) within 5 min to afford a series of novel poly(ether-ester)s based with relatively high average molecular weights (M_w upto approximately 8000). The resulting poly(ether-ester)s were characterized by NMR (¹H and ¹³C), FT-IR spectrometry, SEC measurements and MALDI-TOF mass spectrometry. Thermal properties of the poly(ether-ester)s (4 and 5) were investigated by means of differential scanning calorimetry (DSC).     

New rare earth metal complexes with nitrogen-rich ligands: 5,5'-bitetrazolate and 1,3-bis(tetrazol-5-yl)triazenate-on the borderline between coordination and the formation of salt-like compounds

From the two nitrogen-rich ligands BT(2-) (BT=5,5'-bitetrazole) and BTT(3-) (BTT=1,3-bis(1H-tetrazol-5-yl)triazene), a series of novel rare earth metal complexes were synthesised. For the BT ligand, a vast number of these complexes could be structurally characterised by single-crystal XRD, revealing structures ranging from discrete molecular aggregates to salt-like compounds. The isomorphous complexes [La2(BT)3]14 H2O (1) and [Ce2(BT)3]14 H2O (2) reveal discrete molecules in which one BT(2-) acts as a bridging ligand and two BT groups as chelating ligands. The complexes, [M(BT)(H2O)7]2[BT] x (x) H2O (3-5), (M=Nd (3), Sm (4), and Eu (5)), are also isomorphous and consist of [M(BT)(H2O)7]+ ions in which only one BT(2-) acts as a chelate ligand for each metal centre. [Tb(H2O)8]2[BT]3 x H2O (6) and [Er(H2O)8](2)[BT](3)x H2O (7) are salt-like compounds that do not exhibit any significant metal-nitrogen contacts. In the BTT-samarium compound 9, discrete molecules were found in which BTT(3-) acts as a tridentate ligand with three Sm--N bonds.     

Spectroscopic studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with a N4-macrocylic ligands

Complexes of cobalt(II), nickel(II), copper(II) and zinc(II) with a new tetraaza macrocyclic ligand have been synthesized and characterized by microanalyses, molar conductance, magnetic susceptibility, mass, thermogravimetric (TGA), IR, 1H and 13C NMR, electronic and ESR spectral studies. All the complexes are found to have the formula [MLX2]x nH2O and are six-coordinated with distorted octahedral geometry.