Polyaza Macrocycles Research Articles

Polyaza macrocycles containing the piperazine ring as a semi-flexible moiety

Azamacrocycles 1–4 were synthesized from 9 in 20–30% overall yields. Compounds 1 and 2 extracted some metal ions into organic solvents, but 3 and 4 did not. The crystal structure of the Ag(I) complex of 1 has been determined.

Photophysics of Supercomplexes. Adduct between Ru(bpy)(CN)(4)(2-) and the [32]ane-N(8)H(8)(8+) Polyaza Macrocycle.

The formation of a supercomplex between the Ru(bpy)(CN)(4)(2-) (bpy = 2,2'-bipyridine) complex and the [32]ane-N(8)H(8)(8+) macrocycle (1) has been studied in water and in acetonitrile. In acetonitrile, supercomplex formation is accompanied by (i) large hypsochromic shifts in the absorption spectrum (color changes from deep violet to yellow) and in the emission spectrum, (ii) large anodic shifts in standard oxidation (0.73 V) and reduction (0.37 V) potentials, (iii) typical shifts of (1)H-NMR signals for the macrocycle N-bound protons and the complex bipyridine protons, and (iv) a large increase in the MLCT excited-state lifetime of the complex. In water, the spectral shifts and the changes in standard potential are much less pronounced, but supercomplex formation is evidenced by (13)C-NMR (and (1)H-NMR) and by emission lifetime changes. In both solvents, supercomplex formation is complete in 1:1, 1.0 x 10(-4) M solutions, indicating very large stability constant values. A structure of the supercomplex with the macrocycle bound in a "boat" conformation to the four cyanide ligands of the complex, plausible in terms of molecular models, is consistent with all the experimental data. In water, the supercomplex further associates with added negative species containing carboxylate functions, as shown by partial reversal of the lifetime changes. When the added species is also a potential electron transfer quencher (such as, e.g., Rh(dcb)(3)(3-), dcb = 4,4'-dicarboxy-2,2'-bipyridine), however, association is not accompanied by quenching. This behavior is attributed to the structure of the supercomplex-quencher adduct, in which the macrocycle acts as an insulating spacer between the excited complex and the quencher.

Kinetics of Complex Formation by Macrocyclic Polyaza Polycarboxylate Ligands: Detection and Characterization of an Intermediate in the Eu3+-dota System by Laser-Excited Luminescence

The reaction of Eu{sup 3+} with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate was followed by luminescence of the Eu{sup 3+} center. Reaction kinetics for the formation of intermediates and the final product, [Eu(dota)H{sub 2}O]{sup {minus}}, are reported. The rate limiting step is found to be the rearrangement of EuHdotato from the final product.

ChemInform Abstract: Metal‐Directed Synthesis of Aminobenzyl Polyaza Macrocycles: Candidates for Attachment to Polymers and Biomolecules.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Relaxometry, Luminescence Measurement, Electrophoresis, and Animal Biodistribution of Lanthanide(III) Complexes of Some Polyaza Macrocyclic Acetates Containing Pyridine

Four Gd{sup 3+} complexes [Gd(BP2A){sup +}, Gd(PC2A){sup +}, Gd(PCTA){sup 0}, and Gd(BPO4A){sup {minus}}] with polyazamacrocyclic ligands that contain a pyridine moiety were prepared and examined for possible use as MRI contrast enhancement agents. The authors estimated the number of inner sphere water molecules (q{sub Gd}) for the Gd{sup 3+} complexes from the values of q found for the Tb{sup 3+} and/or Eu{sup 3+} complexes by luminescence lifetime measurements. It was estimated that q{sub Gd} = 3.5, 3.3, 2.4, and 0.2 for Gd(BP2A){sup +}, Gd(PC2A){sup +}, Gd(PCTA){sup 0}, and Gd(BPO4A){sup {minus}}, respectively. The inner sphere relaxivities (r{sub 1,inner}) of these tetraaza macrocyclic complexes were higher than that of Gd(DOTA){sup {minus}} [i.e. 6.79 for Gd(BP2A){sup +}, 6.21 for Gd(PC2A){sup +}, and 4.60 for Gd(PCTA){sup 0} mM{sup {minus}1}s{sup {minus}1} at 40 MHz and 25{degrees}C], but the normalized relaxivities per q{sub Gd} (1.94, 1.88, and 1.92 mM{sup {minus}1}s{sup {minus}1}, respectively) were comparable to that of Gd(DOTA){sup {minus}}. A quantitative treatment of the NMRD profiles based on Solomon-Bloembergen-Morgan theory, using the NMRD profile of Gd(BPO4A){sup {minus}} to correct for an outer sphere contribution, showed that the complexes exhibit characteristics similar to that of Gd(DOTA){sup {minus}} but with shorter electronic relaxation times. Tissue biodistribution results usingmore » radioactive {sup 153}Sm and {sup 159}Gd complexes in rats indicate that the cationic [{sup 153}Sm-(BP2A){sup +} and {sup 153}Sm(PC2A){sup +}] complexes accumulate preferably in the bone tissue while the neutral [{sup 153}Sm-(PCTA){sup 0}] and anionic [{sup 153}Sm(BPO4A){sup {minus}}] complexes appear to have renal clearances similar to those of other low molecular weight contrast agents [i.e. Gd(DTPA){sup 2{minus}} and Gd(DOTA){sup {minus}}].« less

From mononuclear to polynuclear macrocyclic or macroacyclic complexes

The design and synthesis of polydentate Schiff bases and their properties and potential in the selective coordination of metal ions is reviewed. The self-condensation reaction of appropriate formyl or keto precursors with suitable polyamines can give rise to well-defined planar or tridimensional macrocyclic or macroacyclic Schiff bases, but different reaction pathways can also occur. Illustrative examples of [1 + 1], [2 + 2], [2 + 3] condensation products and of unexpected compounds are included. Moreover, the role of metal ions as templating agents and the capability of several Schiff base complexes to undergo transmetallation reactions are reported. Ring expansion and ring contraction processes of the macrocyclic cavity of Schiff bases occur and the experimental conditions for the obtainment or the stabilization of one isomer with respect to the others, in the presence or in the absence of suitable metal ions, are discussed. The preparation of functionalized ligands, containing pendant arms, capable of promoting dynamic complexation-decomplexation processes and their use in selective metal ion transportation and separation are also evaluated. The formation of polydentate, particularly macrocyclic, Schiff base complexes, followed by reductive demetallation with NaBH 4 is also discussed especially for the obtention of more stable, flexible and versatile ligands useful in metal transfer studies. The synthetic strategies for the preparation of macrocyclic and/or macroacyclic mononuclear and polynuclear complexes from these Schiff bases are outlined. For mononuclear and dinuclear complexes only the most recent and significant examples are considered, while particular attention is devoted to the preparation of ligands capable of organizing more than two metal centres into a predetermined arrangement. Different synthetic strategies for the assembly of polynuclear molecular arrays are studied and the synthesis of trinuclear, tetranuclear, hexanuclear, dodecanuclear etc. complexes together with their properties (especially the structural and magnetic aspects) are discussed in detail. In particular the enlargement of the macrocyclic cavity, the introduction of suitable bridging groups or the use of “spacers” between dinuclear entities to obtain polynuclear complexes with predetermined properties are considered in detail. Finally some related systems, such as polyaza macrocycles, compartmental ligands etc., also capable of forming polynuclear systems, are briefly discussed.

ChemInform Abstract: New Conformationally Constrained Polyaza Macrocycles (IV) and (V) Prepared via the Bis(chloroacetamide) Method.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis, characterization and structure of the highly sterically congested complex (3,14-dimethyl-14-nitromethyl-2,6,13,17-tetraazatricyclo[16.4.0.07.12]docos-2-ene)nickel diperchlorate and structure of (3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.07.12]docosa-2,13-diene)nickel diperchlorate

The reaction of the diimine complex [NiL1][ClO4]2(L1= 3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.07.12]docosa-2,13-diene), containing cyclohexane subunits fused to the five-membered chelate rings, with nitromethane in the presence of triethylamine produced the highly sterically congested complex [NiL2][ClO4]2(L2= 3,14-dimethyl-14-nitromethyl-2,6,13,17-tetraazatricyclo[16.4.0.07.12]docos-2-ene) containing one nitromethyl pendant arm. The electronic spectrum of [NiL2]2+ in nitromethane solution shows the d–d band at ca. 490 nm (Iµ= 170 dm3 mol–1 cm–1). The wavelength and the molar absorption coefficient are extraordinarily longer and larger, respectively, than those for square-planar nickel(II) complexes of L1 and other related 14-membered polyaza macrocycles. The crystal structures of [NiL1][ClO4]2 and [NiL2][ClO4]2 revealed that the former has normal square-planar geometry with the nickel atom lying on the N4 plane, whereas the latter has a severely distorted square-planar geometry with the metal atom 0.118 A out of the mean plane of the donor nitrogen atoms. The steric effects of the substituents of the complexes on the geometry and the spectra are discussed. Crystal data: for [NiL1][ClO4]2, monoclinic, space group P21/n, a= 10.423(3), b= 8.9375(6), c= 13.457(3)A, β= 94.459(12)°, Z= 2, R= 0.056 and R′= 0.057 for 2349 independent reflections with Fo2 > 3σ(Fo2); for [NiL2][ClO4]2, monoclinic, space group P21/n, a= 11.968(3), b= 12.6208(14), c= 19.358(6)A, β= 105.008(1 5)°, Z= 4, R= 0.046 and R′= 0.045 for 3382 independent reflections with Fo2 > 3σ(Fo2).

New conformationally constrained polyaza macrocycles prepared via the bis(chloroacetamide) method

The synthesis of two new series of conformationally constrained polyazamacrocycles featuring polysubstitution at macrocycle ring carbons is described.

Chelating Tendencies of Bioactive Aminophosphonates

The metal-binding abilities of a wide variety of bioactive aminophosphonates, from the simple aminoethanephosphonic acids to the rather large macrocyclic polyaza derivatives, are discussed with special emphasis on a comparison of the analogous carboxylic acid and phosphonic acid systems. Examples are given of the biological importance of metal ion – aminophosphonate interactions in living systems, and also of their actual and potential applicability in medicine.

New macrocyclic polyamines of 3,5-disubstituted 1 [formula omitted]-pyrazole. A 13C NMR study of deprotonation and formation of Zn 2+ dinuclear complexes.

Dipodal (2+2) condensation of 3,5-(1 H -pyrazole) dicarbaldehyde ( 3) with 1,5-diamino-3-oxapentane ( 4) and diethylenetriamine ( 5) followed by hydrogenation of the resulting Schiif bases ( 6 and 8), affords two new 26 membered polyaza macrocycles of 1 H -pyrazole ( 7 and 9). The deprotonation of both crowns in basic medium as well as the formation of dinuclear Zn 2+ complexes ( 7b and 9b) from the dipyrazolate salts 7a and 9a have been studied by 13C NMR.

ChemInform Abstract: Binding Properties of Amide and Amide‐Ester N‐Functionalized Polyaza Macrocycles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A new synthetic route to polyaza‐crown macrocycles through the per(N‐formyl)polyaza‐crowns

AbstractSeven new per(N‐formyl)polyaza‐crown macrocycles 1‐7 containing 14 to 21 ring members have been synthesized in yields of over 40% via the cyclization reaction of the appropriate per(N‐formyl)polyamine 11‐13 with the appropriate ditosylate, dibromide or diiodide. Three of the per(N‐formyl) macrocycles 5‐7 were hydrolyzed under acidic conditions to give the unsubstituted polyaza macrocycles 8‐10 in yields of over 77%.

Kinetics of electron-transfer reactions of the Co(bpyO2)32+/3+ couple in acetonitrile

The kinetics of the outer-sphere electron transfer reactions of tris(1,1′-dioxo-2,2′-bipyridine)cobalt(II) and (III) with a series of nickel polyaza macrocycles, FeL3n+ and OsL32+ complexes (L is 2,2′-bipyridine or 1,10-phenanthroline, and substituted derivatives), and Rh2(O2CCH3)4(CH3CN)2+ have been investigated in acetonitrile at 25.0 °C. An application of the Marcus theory relationship to the cross-reaction rate constants yielded apparent Co(bpyO2)32+/3+ self-exchange rate constants of 102 M−1 s−1 from the nickel macrocycle cross-reactions and 10−1 M−1 s−1 from the cross-reactions with the metal polypyridine complexes. The latter cross-reactions are considered to be non-adiabatic due to a mismatch in the donor/acceptor orbital symmetries. The electron exchange rate constant is compared with the exchange rate constants for other Co(II)/Co(III) complex couples and M(bpyO2)32+/3+ couples of other first-row transition metals, and discussed in terms of inner-sphere and solvent reorganization barriers. Keywords: electron transfer, Marcus theory relationship, cobalt(II)/(III) couples, 1,1′-dioxo-2,2′-bipyridine.

Binding properties of amide and amide–ester N-functionalised polyaza macrocycles

A series of amide and amide–ester N-functionalised coronads has been prepared based on [12]- N2O2, [15]-N2O3 and [18]- N2O4 polyazoaxa macrocycles. Complexation of certain alkali and alkaline-earth metal cations has been monitored by 13C NMR and IR spectroscopy, enthalpies of complexation measured in methanolic solution by calorimetry and stability constants measured in aqueous solution by potentiometric methods. Strong complexation of Ca2+ in aqueous solution was observed with high selectivities (ca. 102 to 103.5) over Na+ and K+.

Synthesis and complexation properties of a new macrocyclic polyaza polyphosphinate ligand, DOTEP (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methyleneethylphosphinate))

Synthesis and complexation properties of a new macrocyclic polyaza polyphosphinate ligand, DOTEP (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methyleneethylphosphinate))

Complexation of Transition Metal Ions with Substituted Aza Macrocycles: Induction of Columnar Mesophases by Molecular Recognition

The influence of molecule dynamics on the phase properties is evident in the polyaza macrocycle 1 and the corresponding amide (CO in place of CH2 groups). The amide, but not 1, forms a columnar discotic mesophase, because of the restricted rotation of the side groups, which results from the partial double bond character of the exocyclic CN bond. Compound 1 needs to be coordinated, for example to cobalt ions, to fix its conformation and thus to induce a liquid crystalline phase. The preliminary susceptibility measurements on an analogous copper complex suggests an electronic coupling between the metal ions.

Synthesis of selectively protected polyaza macrocycles

A general route to selectively protected polyaza macrocycles has been developed using a mixture of diethylphosphoryl and tosyl groups for protection of linear chain polyamines. Condensation of N-(diethoxyphosphoryl)-N',N″-ditosydiethylenetriamine (1a), N,N″-bis(diethoxyphosphoryl)-N'-tosyldiethylenetriamine (1b) and N,N',N″-tris(diethoxyphosphoryl) diethylenetriamine (1c) with mesylates or tosylates 2 gave the corresponding macrocycles 3 in reasonable yield. The phosphoryl group was selectively removed with gaseous HCl in excellent yield

ChemInform Abstract: Synthesis and Binding Properties of Amide‐Functionalised Polyaza Macrocycles.

AbstractThe title compounds (III), (V), (VII), (X), (XII), (XIII), and (XIV) are prepared according to procedures indicated in the scheme.

The Electrochemical Study of Ag(II) Complexes of Polyaza Macrocycles and Their Acetic Acid Derivatives

Abstract Although an attempt to isolate pure crystallines of Ag(II) complexes failed, we could prepare stable aqueous solutions of the Ag(II) complexes of [15]aneN5, [16]aneN5, and their acetic acid derivatives by disproportionation reactions of Ag(I) induced by these polyaza macrocycles, and have investigated their electrochemical redox behaviors using conventional voltammetric methods. All Ag(II) complexes including the [14]aneN4 (cyclam) complex undergo a reversible two-electron reduction at DME (dropping mercury electrode). From the potential where the i2⁄(i1–i) ratio is unity, the log formation constants were determined to be 43.4, 43.6, 43.3, 39.3, and 42.5 for the cyclam, [15]aneN5, [16]aneN5, cyclam-tetraacetic acid, and [15]ane5-pentaacetic acid complexes, respectively. Cyclic voltammetric (CV) oxidation scans at the glassy carbon electrode showed a reversible one-electron response (separation of anodic and cathodic peak potentials, ΔEp′=70 mV; the ratio of anodic and cathodic peaks, (ip)c⁄(ip)a′=1), which can be ascribed to a reversible Ag(III)/Ag(II) redox change. Though the acetate groups attached to the nitrogen atoms contribute to the net destabilization of the Ag(II) complexes, they exert a large positive effect on the thermodynamic stability of the Ag(III) state.