Iron(III) activation hits a [4 + 4] macrocycle

The tetranuclear complex [Fe(III)2(L')(OH)(CH3O)]2, 1, has been synthesised from the reaction of either ferrous [in excess as 4:1 or stoichiometric 2:1 iron(II) : H4L] or ferric ions [4:1 iron(III) : H4L] with the large macrocycle, H4L, using aerobic conditions in methanol in the presence of triethylamine. The structure of 1 was determined by single-crystal X-ray diffraction. These reaction conditions lead to the modification of the original macrocycle through the incorporation of a methylene group between two amine groups to give an imidazolidine ring in (L')4-. The controlled addition of formaldehyde into the reaction system results in a significantly improved yield of 1, suggesting that it is involved in the reaction mechanism. The (L')4- macrocycle binds to two, well-separated, iron(III) centres [Fe(1)...Fe(1a) > 8 A]. Each iron(III) centre is further linked via hydroxy and methoxy bridges to equivalent iron(iii) centres contained in a second macrocycle. Overall this gives a structure containing two {Fe(OH)(CH(3)O)Fe} dimers [Fe(1)...Fe(2)ca. 3.2 A] sandwiched by two (L')4- macrocycles. The complex was further characterised by SQUID magnetic measurements and can be interpreted in terms of two isolated antiferromagnetically coupled Fe(III) dimers (J=-23.75 K).     

Tautomerization in naphthalenediimines: a keto-enamine Schiff base macrocycle

[reaction: see text] A new [3 + 3] Schiff base macrocycle incorporating naphthalene groups has been prepared. By examination of its properties, X-ray crystallography of model compounds, and calculations, it has been determined that the macrocycle exists predominantly as the keto-enamine tautomer. This unexpected tautomerization presents an unusual hexaketo interior in the macrocycle.     

Ligand influence over the formation of dinuclear [2+2] versus trinuclear [3+3] Cu(I) Schiff base macrocyclic complexes

The preparation and characterization of three new macrocyclic ligands with pendant arms based on the [2+2] condensation of isophthalaldehyde and the corresponding triamine substituted at the central N-atom is reported. None of these new macrocyclic ligands undergo any equilibrium reaction, based on imine hydrolysis to generate [1+1] macrocyclic formation or higher oligomeric compounds, such as [3+3], [4+4], etc., at least within the time scale of days. This indicates the stability of the newly generated imine bond. In sharp contrast, the reaction of the [2+2] macrocyclic Schiff bases with Cu(I) generates the corresponding dinuclear Cu(I) complexes [Cu(2)(L(1))](2+), 1(2+); [Cu(2)(L(2))(CH(3)CN)(2)](2+), 2(2+); and [Cu(2)(L(3))(CH(3)CN)(2)](2+), 3(2+), together with their trinuclear Cu(I) homologues [Cu(3)(L(4))](3+), 4(3+); [Cu(3)(L(5))(CH(3)CN)(3)](3+), 5(3+); and [Cu(3)(L(6))(CH(3)CN)(3)](3+), 6(3+), where the [2+2] ligand has undergone an expansion to the corresponding [3+3] Schiff base that is denoted as L(4), L(5), or L(6). The conditions under which the dinuclear and trinuclear complexes are formed were analyzed in terms of solvent dependence and synthetic pathways. The new complexes are characterized in solution by NMR, UV-vis, and MS spectroscopy and in the solid state by X-ray diffraction analysis and IR spectroscopy. For the particular case of the L(2) ligand, MS spectroscopy is also used to monitor the metal assisted transformation where the dinuclear complex 2(2+) is transformed into the trinuclear complex 5(3+). The Cu(I) complexes described here, in general, react slowly (within the time scale of days) with molecular oxygen, except for the ones containing the phenolic ligands 2(2+) and 5(3+) that react a bit faster.     

Social and antisocial [3 + 3] Schiff base macrocycles with isomeric backbones

Two new conjugated macrocycles have been prepared in high yield using Schiff base condensation. These are the first Schiff base macrocycles to incorporate phenanthrene, and they contain 66 and 78 atoms, respectively, in their smallest closed ring. Although the backbones of the two macrocycles have nearly the same constitution, one aggregates in chloroform while the other does not. This is rationalized based on the differential overlap of aromatic components in the dimers.     

A new calix[4]arene Schiff base sensor for Hg<Superscript>2+</Superscript> and Au<Superscript>3+</Superscript>

This article reports the selective sensing ability of a newly synthesized calix[4]arene Schiff base (C4TSB) derivative. C4TSB exhibited strong turn-off fluorescence affinity for Hg²⁺ and Au³⁺. The selective sensing ability of receptor was investigated in the presence of different co-existing competing ions. The limit of detection for Hg²⁺ and Au³⁺ was determined as 1.9 × 10^?5 and 1.0 × 10^?6 M, respectively. Receptor forms 1:1 stoichiometric complex with both metals and their binding constants were calculated as 7.9 × 10³ M^?1 for Hg²⁺ and 5.7 × 10³ M^?1 for Au³⁺. Complexes were also characterized through FT-IR spectroscopy.     

Formation of a silicon‐containing macrocycle with a pyridoxalimine Schiff base ligand

The reaction of dichlorodiphenylsilane with a polydentate Schiff base ligand derived from pyridoxal and 2‐hydroxyaniline yields the macrocyclic centrosymmetric silicon compound 9,27‐dimethyl‐3,3,21,21‐tetraphenyl‐2,4,20,22‐tetraoxa‐8,13,26,31‐tetraaza‐3,21‐disilapentacyclo[30.4.0.0^6,11.0^14,19.0^24,29]hexatrideca‐1(32),6,8,10,12,14,16,18,24,26,28,30,33,35‐tetradecaene‐10,28‐diol chloroform tetrasolvate, C₅₂H₄₄N₄O₆Si₂·4CHCl₃. The asymmetric unit contains half of the macrocycle and two molecules of chloroform, with C—H...O and C—H...N contacts binding the two guests to the host in the crystal structure. This macrocyclic silicon compound represents a promising host for molecular‐recognition processes and for the construction of nanostructures.     

Heterodinuclear Ln[bond]Na complexes with an asymmetrical macrocyclic compartmental Schiff base

Heterodinuclear lanthanide(III)-sodium(I) complexes [LnNa(L)(Cl)(2)(CH(3)OH)] (Ln=La[bond]Nd, Sm[bond]Lu), where H(2)L is a [1+1] asymmetric compartmental macrocyclic ligand containing a N(3)O(2) Schiff base and a O(3)O(2) crown-ether-like coordination site, have been prepared and characterized by IR, (1)H, (13)C, and (23)Na NMR spectroscopy, mass spectrometry, and electron microscopy. In the solid state, the lanthanide(III) ions coordinate the Schiff-base N(3)O(2) site, and the sodium ion occupies the O(3)O(2) crownlike cavity, as shown by the X-ray crystal structures of the Nd, Eu, Gd, and Yb derivatives. In these complexes, the lanthanide(III) ion is coordinated by two chlorine atoms in the trans position and by three nitrogen and two negatively charged phenol oxygen atoms of the Schiff base, and the ion is heptacoordinated with a pentagonal bipyramidal geometry. The sodium ion is coordinated by three etheric oxygen atoms and the two phenolic oxygens that act as a bridge. A methanol molecule is also coordinated in the apical position of the resulting pentagonal pyramidal polyhedron. A detailed (1)H and (13)C NMR study was carried out in CD(3)OD for both diamagnetic and paramagnetic heterodinuclear complexes [LnNa(L)(Cl)(2)(CH(3)OH)]. The complexes are also isostructural in solution, and their structures parallel those found in the solid state. Moreover, some significative distances determined in the solid state and in solution are comparable. Finally, the potential use of these complexes as molecular probes for the selective recognition of specific metal ions has been tested. In particular, their ability to act as shift reagents and the selectivity of the O(3)O(2) site towards Li(+), Ca(2+), and K(+) were investigated by (23)Na NMR spectroscopy.     

Microwave assisted synthesis of 72-membered chiral hexanuclear [6+6] macrocyclic Schiff base

A novel double thicalix[4]arene possessing two amide sites was prepared. The binding behavior with Ag⁺ has been examined by ¹H NMR titration experiment. The association constants K _ass of the amide sites are quite similar (K _ass = 2.10 × 10⁴ M⁻¹ and K _ass = 2.00 × 10⁴ M⁻¹), suggesting that the two amide sites work independently.     

Calix[4]pyrrole Schiff base macrocycles. Novel binucleating ligands for mu-oxo iron complexes

New bimetallic mu-oxo diferric complexes of several previously reported calix[4]pyrrole Schiff base macrocycles are described. The synthesis of a new member of this class of macrocycles is also reported; it was prepared via an acid-catalyzed condensation between 1,9-bisformyl-5,5-dipropyldipyrromethane and o-phenylenediamine. Reactions of the free base macrocycles or their bis-HCl salts with Fe(II) mesitylene, followed by air oxidation, gave the binuclear mu-oxo bis-Fe(III) compounds 6-10 in moderate yield. X-ray crystallography data reveal two different coordination environments for the Fe-O-Fe subunit in 6-10 that it is suggested can be controlled by altering the reaction conditions. Structural properties of these metalated pyrrolic macrocycles are also compared to those of mu-oxo diferric porphyrins and mu-oxo diferric texaphyrin. Complexes 6-10 exhibit two distinct types of M-N bonds that are similar in length to the bonds observed in metallotexaphyrin complexes. However, the electronics of the present systems are very different from those of texaphyrins and porphyrins in that no delocalized bonding patterns are observed within the ligands as a whole.     

DFT study on [4+2] and [2+2] cycloadditions to [60] fullerene

The functionalisation of C₆₀ fullerene with 2,3-dimethylene-1,4-dioxane (I) and 2,5-dioxabicyclo [4.2.0]octa-1(8),6-diene (II) was investigated by the use of density functional theory calculations in terms of its energetic, structural, field emission, and electronic properties. The functionalisation of C₆₀ with I was previously reported experimentally. The I and II molecules are preferentially attached to a C—C bond shared and located between two hexagons of C₆₀ via [4+2] and [2+2] cycloadditions bearing reaction energies of ?15.9 kcal mol^?1 and ?72.4 kcal mol^?1, respectively. The HOMO-LUMO energy gap and work function of C₆₀ are significantly reduced following completion of the reactions. The field electron emission current of the C₆₀ surface will increase after functionalisation of either the I or II molecule.     

Versatile formation of [2]catenane and [2]pseudorotaxane structures; threading and noncovalent stoppering by a self-assembled macrocycle

A self-assembled dimeric macrocycle between 4,4'-bis(4-pyridylmethoxy)biphenyl (L) and (en)Pd(NO(3))(2) was constructed, and its interactions with cyclodextrins of different cavity size resulted in the formation of [2]catenane and [2]pseudorotaxane systems, respectively. The structures were identified by 1D and 2D NMR spectroscopy and cold spray ionization mass (CSI-MS) spectrometry.     

Photochemical rearrangement of calix[4]arene-derived bis(spirodienones): formation of a new macrocycle

Bis(spirodienones) of calix[4]arene undergo a facile photochemical rearrangement leading to a new macrocycle having a spirocyclic cyclopentenone-THF unit, a trisubstituted phenol, and a benzofuran moiety. The macrocyclic ring system has a 14-membered irregular cavity and resembles a partial bowl in the solid state.     

Calix[4]arene Schiff bases—potential ligands for fluorescent studies

A series of novel double-armed calix[4]arene derivatives incorporating imine substituents were synthesised from the Schiff-base reaction of 25,27-bis[2-[(1-formyl-2-phenyl)oxy]ethyl]-p-tert-butylcalix[4]arene (1) with the appropriate amine or hydrazone. All compounds were characterised by various spectroscopic and analytical techniques, and in three cases, by X-ray crystallographic studies. In the case of compound 2, inclusion compounds were synthesised with both m-xylene and dimethylformamide and their X-ray structures revealed these inclusion sites—between the pendant arms and in the upper cavity, respectively. In all cases, the pendant arms are bent away from each rather than adopting a face-to-face conformation.     

Synthesis and properties of dimetallic M1[Pz]-M2[Schiff base] complexes

We report the synthesis and physical characterization of a series of peripherally functionalized porphyrazines (pz's) 1[M(1); M(2); R], where M(1) is a metal ion incorporated into the pz core, M(2) is a metal ion bound to a bis(5-tert-butyl-salicylidenimine) chelate built onto two amino nitrogen attached to the pz periphery, and R is a solubilizing group (either n-propyl (Pr) or 3,4,5-trimethoxyphenyl (TMP) group) attached to the remaining carbons of the pz periphery. The 1[M(1); M(2); R] species are prepared from precursor pz's with a selenodiazole ring; they are deprotected to form the diamino pz, which reacts with two moles of 5-tert-butyl-2-hydroxybenzaldehyde to form the Schiff base pz. This is metalated to form 1[M(1); M(2); R]. The crystal structures of 1[2H; Ni; Pr] and 1[Cu; ClMn; Pr] are presented. The EPR spectra of the M(1)-M(2) "isomers" prepared with Cu(II) (S = (1)/(2)) and ClMn(III) (S = 2) ions, 1[ClMn; Cu; Pr] and 1[Cu; ClMn; TMP], are a superposition of spectra expected for the S = (3)/(2) and S = (5)/(2) total-spin manifolds that result from strong Heisenberg coupling between the partner spins. The exchange splitting between the two manifolds, as determined by temperature-dependent magnetic susceptibility measurements, is equivalent for the two M(1)-M(2) "isomers", Delta/k(B) approximately 20-25 K, which suggests a sigma-pathway for exchange coupling.     

Enantioselective Brønsted base catalyzed [4+2] cycloaddition using novel amino-substituted tetraphenylene derivatives

This paper is concerned with the syntheses of 1,8,9,16-tetrahydroxytetraphenylene derivatives and their applications as Brønsted base organocatalysts for [4+2] cycloaddition between anthrone and maleimides. The structural modifications of the catalysts and their related catalytic properties are described and discussed in details.     

NMR study of bis-4-fluoroaniline Schiff base of gossypol

The title compound has been prepared. Using ¹H NMR, ¹³C NMR and selected decoupling method, the compound is shown in the keto-form. DNMR method was used to investigated the exchange between NH in the title compound and water in DMSO-d₆. The rate process was calculated by complete line shape analysis method and activation parameters ΔH≠, ΔG≠ and ΔS≠ were found to be 8.4±0.5 kcalmol^?1, 16.9±0.2 kcalmol^?1 and ?26.9±1.5 calmol^?1 k^?1 respectively.