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.     

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.     

Chromium(III) complexes bearing bis(benzotriazolyl)pyridine ligands: synthesis,characterization and ethylene polymerization behavior

Reaction of benzotriazole with 2,6-bis(bromomethyl)pyridine and 2,6-pyridinedicarbonyl dichloride yields the tridentate ligands 2,6-bis(benzotriazol-1-ylmethyl)pyridine (1) and 2,6-bis(benzotriazol-1-ylcarbonyl) pyridine (2). The molecular structures of the ligands were determined by single-crystal X-ray diffraction. These ligands react with CrCl₃(THF)₃ in THF to form neutral complexes, [CrCl₃{2,6-bis(benzotriazolyl)pyridine-N,N,N}] (3, 4), which are isolated in high yields as air stable green solids and characterized by mass spectra (ESI), FTIR spectroscopy, UV–Visible, thermogravimetric analysis (TGA), and magnetic measurements. After reaction with methylaluminoxane (MAO), the chromium(III) complexes are active in the polymerization of ethylene showing a bimodal molecular weight distribution. A DFT computational investigation of the polymerization reaction mechanism shows that the most likely reaction pathway originates from the mer configuration when the spacer is CH₂ (complex 3) and from the fac configuration when the spacer is CO (complex 4).     

Fluxional rearrangement in congested ruthenium(II) complexes containing pyrimidine- and/or pyridine-based dithioether ligands

The solvento species obtained by the treatment of cis-RuCl₂(N,N-L)₂ [L = di-2-pyridyl sulfide (dps), di-2-pyrimidyl sulfide (dprs)] with AgPF₆, reacted with dithioethers L′ [L′ = 2,6-bis(2-pyridylthiomethyl)pyridine (pytmp), 2,6-bis(2-pyrimidylthiomethyl)pyridine (prtmp) and 2,6-bis{2-(4-methyl)pyrimidylthiomethyl} pyridine (mprtmp)] to afford the compounds [Ru(N,N-L)₂(N,S-L′)][PF₆]₂. The ¹H NMR spectra indicate that L′ is chelated through S and N atoms with the formation of a four-membered ring. As a consequence, the ruthenium and sulfur atoms are stereogenic centers with ∆ and Λ and (R) and (S) configurations, respectively. NMR spectra, at low temperatures, show that two invertomers, of similar abundance, as enantiomeric couples ∆S, ΛR and ∆R, ΛS are present. In the methylene region, four AB systems are observed that in both the species contain two non-equivalent methylene groups. Variable-temperature NMR spectra and EXSY experiments show that the sulfur inversion produces an exchange between the invertomers. The one-dimensional band-shape analysis of the exchanging methylene signals showed that the energy barriers for the process are in the 43–52 kJ mol⁻¹ range. The possible mechanisms of the sulfur inversion are discussed.     

Four Novel 30-Membered Imine and Amine Macrocycles Derived from Ortho-Aminophenyl Diamines

Two novel macrocyclic tetra-imine-diphenol Schiff base (H₂L₁ and H₂L₂) were synthesized by [2 + 2] cyclocondensation of ortho-aminophenyl diamines [1,2-bis(2′-aminophenoxy)benzene (I) and 1,2-bis(2′-aminophenoxy)-4-t-butylbenzene (II)] with 2,6-diformyl-4-methylphenol. Two novel tetra-amine-diphenol macrocycles (H₂L₃ and H₂L₄) have been obtained by reduction of the imine analogs with NaBH₄ in MeOH/CHCl₃.     

Multidentate bis(pyrazolylmethyl)pyridine ligands: coordination chemistry and binding properties with zinc(II) and cadmium(II) cations

The coordination chemistry and cationic binding properties of 2,6-bis(pyrazol-1-ylmethyl)pyridine (L1), 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L2), and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (L3) with zinc(II) and cadmium(II) have been investigated. Reactions of L2 with zinc(II) and cadmium(II) nitrate or chloride salts produced monometallic complexes [Zn(NO₃)₂(L2)] (1), [ZnCl₂(L2)] (2), [Cd(NO₃)₂(L2)] (3), and [CdCl₂(L2)] (4). Solid state structures of 1 and 3 confirmed that L2 binds in a tridentate mode. While the nitrates in the zinc complex (1) adopt monodentate binding fashion, in cadmium complex (3), they exhibit bidentate mode. L1–L3 show binding efficiencies of 99% for zinc(II), 60% for lead(II), and 30% for cadmium(II) cations from aqueous solutions of the metal ions. Theoretical studies using Density Functional Theory were consistent with the observed extraction results.     

Chromium(III) complexes with terdentate 2,6-bis(azolylmethyl)pyridine ligands: Synthesis, structures and ethylene polymerization behavior

Reactions of 2,6-bis(bromomethyl)pyridine with 3,5-dimethylpyrazole and 1H-indazole yield the terdentate ligands 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (5) and 2,6-bis(indazol-2-ylmethyl)pyridine (6). The molecular structure of the new compound 6 was determined by single-crystal X-ray diffraction. These ligands react with the CrCl₃(THF)₃ complex in THF to form neutral complexes of general formula [CrCl₃{2,6-bis(azolylmethyl)pyridine-N,N,N}] (7, 8) which are isolated in high yields as stable green solids and characterized by means of elemental analysis, magnetic moments, IR, and mass spectroscopy. Theoretical calculations predict that the thermodynamically preferred structure of the complexes is the fac configuration. After reaction with methylaluminoxane (MAO) the chromium(III) complexes are active in the polymerization of ethylene.     

Nontemplate Synthesis of Two Novel 23-Membered N3O4-Donor Macrocycles

Abstract

A novel 23-membered heptadentate N₃O₄ Schiff base ligand has been prepared by [1 + 1] cyclocondensation of 1,2-bis(2′-aminophenoxy)-4-t-butylbenzene with 2,6-bis(2-formylphenoxymethyl)pyridine by a nontemplate procedure. Treatment of L₁ with NaBH₄ in EtOH/CHCl₃ gave the di-amine macrocycle L_2.     

A New Hybrid Cmpo/Nopopo Ligand: Synthesis and Selected Lanthanide Coordination Chemistry

Abstract

A two-step synthesis for 2,6-bis[(diphenyl)-N,N-diethylcarbamoylmethylphosphine oxide]pyridine N-oxide (3) from 2,6-bis[(diphenylphosphinoyl)methyl]pyridine is reported along with coordination chemistry with Dy(III) and Yb(III). Crystal structure determinations for the ligand 3_S,S and 1:1 complexes [Dy(3_R,S )(NO₃)₃]·(Me₂CO) and [Yb(3_R,S )(NO₃)₃]·(Me₂CO) are described. In these complexes, the pentafunctional ligand 3 coordinates in a tridentate NOPOPO chelate mode.     

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 of propionamide pyridine and pyridine n‐oxide ligands

A new set of pyridine and pyridine N‐oxides functionalized with N,N‐dimethylpropionamide pendant groups in the 2‐ and 2,6‐positions have been prepared from the combination of 2‐chloromethylpyridine and 2,6‐bis(chloromethyl) pyridine with α‐lithio N,N‐dimethyl acetamide. The coordination interaction between 2‐(N,N‐dimethylpropionamide) pyridine N‐oxide ( 10 ) and Tb(NO₃)₃ has been unambiguously defined via single crystal X‐ray diffraction analysis of Tb( 10 )(NO₃)₃(H₂O).     

Syntheses and crystal structures of neutral oxorhenium(V) complexes of N2O2-donor tripodal ligands

The neutral distorted octahedral complexes [ReOCl(L)] {H₂L = N,N-bis(2-hydroxybenzyl)-2-(2-aminoethyl)dimethylamine (H₂had); N,N-bis(2-hydroxybenzyl)-aminomethylpyridine (H₂hap); N,N-bis(2-hydroxybenzyl)-2-(2-aminoethyl)pyridine (H₂hae)} were prepared by the reaction of trans-[ReOCl₃(PPh₃)₂] with a twofold molar excess of H₂L in ethanol. X-ray structure determinations of [ReOCl(had)] (1) and [ReOCl(hap)] (2) were performed, and the structures compared. In both complexes the choride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen.     

Models for Copper-Dioxygen Complexes: The chemistry of copper(II) with some planar tridentate nitrogen ligands

The solution chemistry of Cu(II) with a series of five planar tridentate nitrogen ligands, 2,6-bis(benzimidazol-2-yl)pyridine (bzimpy, 1 ), 2,6-bis(l-methylbenzimidazol-2-yl)pyridine (mbzimpy, 2 ) 2,6-bis(benzothiazol-2-yl) pyridine (bzthpy, 3 ), 2,6-bis(benzoxazol-2-yl)pyridine (bzoxpy, 4 ), and 2,2′, 6′, 2″-terpyridyl (terpy, 5 ) is reported. Electronic and EPR spectra are consistent with the complexes [CuL]²⁺ having essentially tetragonal structure in solution, with the fourth coordination site in the plane of the ligand occupied by solvent. bzthpy and bzoxpy show smaller ligand-field splittings than bzimpy, mbzimpy, and terpy, and are easily decomplexed from the copper. Substitution of the coordinated solvent molecule in the plane of the ligand is observed with Cl^? and OH^? (provided that the ligand has no acidic protons) for all ligands except terpy. The reaction between [Cu(mbzimpy)]²⁺ and imidazole has been studied by potentiometric titration in MeCN/H₂O 1:1 and shows strong binding of the imidazole in the plane (log K = 4.5 at 25°), and also the formation of an imidazolate-bridged dinuclear species.     

The formation of 'classical' and 'half unit' Schiff-base ligands from their components on a molybdenum(IV) centre

The in situ synthesis of the complex, (PPh₄)[Mo(CN)₃O(aceen)] (aceen = N-[1-(pyridin-2-yl)ethylidene]ethane-1,2-diamine), with a 'half unit' Schiff base ligand (with a free amino group) is described and compared with that of [Mo(CN)₂O(diaceen)]·H₂O (diaceen = N,N-bis[1-(pyridin-2-yl)ethylidene]ethane-1,2-diamine) in which a 'classical', tetradentate Schiff base ligand is formed. The mechanism of the 'half unit' and 'classical' template Schiff bases ligand formation is discussed.     

Microwave-Promoted Syntheses of Pyridine Carboxamides and tert-Carboximides from Novel 6-Acetylpyridine-2-carboxylic Acid

A novel 6-acetylpyridine-2-carboxylic acid (4) was obtained occasionally during the synthesis of asymmetric ethyl 6-acetylpyridine-2-carboxylate (3) from 2,6-dipiclinic acid (1). Compounds 3 and 4 could transform mutually under some specific conditions. Two reactions of distinctive types occurred when they reacted with the aromatic amines as precursors, due to different functional groups on the 2-position of pyridine in the molecules of 3 and 4: one was Schiff base condensation and the other was an amidation reaction. From the latter reaction, two series of new compounds, pyridine carboxamides (5a–d) and pyridine tert-carboximides (6a–h), resulted. The relevant reaction mechanism is discussed in detail.     

Synthesis,crystal structure and catalytic performance of bis (imino)pyridyl nickel complexes

Two new Ni(II) complexes of 2,6-bis[1-(2,6-diethylphenylimino)ethyl]pyridine (L¹), 2,6-bis[1-(4-methylphenylimino)ethyl]pyridine (L² ) have been synthesized and structurally characterized. Complex Ni(L¹)Cl₂?·?CH₃CN (1), exhibits a distorted trigonal bipyramidal geometry, whereas complex Ni(L¹)(CH₃CN)Cl₂ (2), is six-coordinate with a geometry that can best be described as distorted octahedral. The catalytic activities of complexes 1, 2, Ni{2,6-bis[1-(2,6-diisopropyl-phenylimino)ethyl]pyridine} Cl₂?·?CH₃CN (3), and Ni{2,6-bis[1-(2,6-dimethylphenylimino) ethyl]pyridine}Cl₂?·?CH₃CN (4), for ethylene polymerization were studied under activation with MAO.     

Metal chelates of ligands containing the ONS donor grouping,part I. Metal chelates of Schiff bases derived from fluorinatedβ-diketones and thiosemicarbazide

Summary The Schiff bases RC(OFl)=CFlC(CF₃)=NNlJC(S)NH₂ (R = 2-thienyl, Ph,p-BrC₆H₄,p-MeC₆H₄,p-MeOC₆H₄,m-McOC₆H₄, -naphthy], Prⁱ) have been prepared by condensation of fluorinated -diketones with thiosemicarbazide. By the loss of one or two protons from their tautomeric iminothiol form RC(OH)=CHC(CF₃)=NN=C(SH)NH₂ the Schiff bases act as (i) doubly negatively charged ONS tridentate or (ii) singly negatively charged NS bidentate ligands, respectively. The Schiff bases give dimeric µ₂-dithiolo-bridged complexes M(ONS)₂ (M = Ni, Pd, and Pt). The thiolo-bridges in the nickel complexes can be split by reaction with pyridine to give the monomeric compounds Ni(ONS)py, whereas the palladium and platinum complexes are unreactive towards pyridine. When R = 2-thienyl orp-BrC₆H₄, 1:2 complexes of the type M(HONS)₂ (M = Pd or Pt) were isolated. With copper(II) the Schiff bases yield the complexes Cu^II(ONS). Cu^I(HONS) which are considered to have a polymeric structure involving -thiolo-bridges.     

A new Schiff-base as fluorescent chemosensor for selective detection of Cr3+: An experimental and theoretical study

A novel Schiff base fluorescent sensor N,N′-bis(salicylidene)-2,6-bis(4-aminophenyl)-4-phenylpyridine (P3) was synthesized through condensation of 2,6-bis(4-aminophenyl)-4-phenylpyridine and 2-hydroxybenzaldehyde. The obtained results from fluorescence analysis revealed that by excess of Cr³⁺ to P3, a remarkable increase was observed in the fluorescent intensity of the Schiff base at 663?nm with the ratio of CH₃CN/H₂O (95/5%), even though the other cations would likely have no impact on the fluorescence intensity. The cause of this trend might be ascribed to the formation of a 1:1 stoichiometric P3-Cr³⁺ complex, confirmed by Job's plot, which is resulted in preventing the photo-induced electron transfer (PET) process. From fluorescence titration, the association constant K_a was gained 2.28?×?10⁵?M^?1 and the limit of detection (LOD) was determined to be 1.3?×?10^?7?M. Furthermore, the optimized structure together with the electronic spectra of the proposed complex was determined by DFT and TDDFT calculations.     

Aldimine 2,6-bis(imino)pyridine iron(II) and cobalt(II)/methyl aluminoxane catalyst systems for polymerization of <Emphasis Type="Italic">tert-</Emphasis>butylacrylate

Aldimine 2,6-bis[(imino)methyl]pyridine iron(II) (1, 4, and 6) and cobalt(II) (3 and 5) complexes bearing bulky cycloaliphatic (bornyl and myrtanyl) or aromatic (naphthyl) terminal groups have been applied successfully, after activation with methyl aluminoxane (MAO), as catalysts for the polymerization of tert-butylacrylate. For comparison reasons, complex 2 that contains the ketimine ligand, 2,6-bis[(−)-cis-myrtanylimino)ethyl]pyridine (BMEP), has also been utilized. All studied complexes showed moderate polymerization activities, and they produced high molar mass syndiorich-atactic polymers. Surprisingly, the aldimine-based catalyst systems showed comparable activities compared with the corresponding ketimine complex (2), and they produced high molar mass polymers. In addition, complexes with bulky terminal cycloaliphatic substituents on the tridentate aldimine ligands showed higher polymerization activity compared with the aromatic ones (6). Polymerization activity and polymer molar masses are dependent on the ligand framework.