Water-soluble calix[4]resorcarenes as enantioselective NMR shift reagents for aromatic compounds

A tetra L-prolinylmethyl derivative of a tetra-sulfonated calix[4]resorcarene (1) is an effective chiral NMR solvating agent for water-soluble compounds with phenyl, pyridyl, bicyclic aromatic, or indole rings. These aromatic compounds form host-guest complexes with the calix[4]resorcarene in water. Complexation of substrates with the calix[4]resorcarene is likely promoted by hydrophobic effects, and bicyclic substrates have association constants with the calix[4]resorcarene larger than those of similar phenyl-containing compounds. Aromatic resonances of the substrates show substantial upfield shifts because of shielding from the aromatic rings of the calix[4]resorcarene, and several resonances in the 1H NMR spectra typically exhibit enantiomeric discrimination. The extent of enantiomeric discrimination depends in part on interactions of the substituent groups of the substrates with the prolinylmethyl groups of the calix[4]resorcarene. The effectiveness of a calix[4]resorcarene prepared from N-methyl-L-alanine (2) as a chiral NMR discriminating agent is compared to the L-prolinylmethyl derivative.     

Calix[4]arene-based ditopic receptors for simultaneous recognition of fluoride and cobalt(II) ions

A series of calix[4]arene based ditopic receptors possessing bipyridyl and hydrazone units have been synthesized and evaluated for ionic recognition. It has been observed that the synthesized derivatives function as allosteric receptors for simultaneous recognition of Co²⁺and F^? ions through non-covalent interactions. Significant bathochromic shifts in the UV–visible spectrum with a profound colour change promise their use to engineer novel applications.     

Cycloalkane and alicyclic heterocycle complexation by new switchable resorcin[4]arene-based container molecules: NMR and ITC binding studies

The synthesis and structural characterization of novel, "molecular basket"-type bridged cavitands is reported. The resorcin[4]arene-based container molecules feature well-defined cavities that bind a wide variety of cycloalkanes and alicyclic heterocycles. Association constants (K(a)) of the 1:1 inclusion complexes were determined by both (1)H NMR and isothermal titration calorimetry (ITC). The obtained K(a) values in mesitylene ranged from 1.7×10(2) M(-1) for cycloheptane up to 1.7×10(7) M(-1) for morpholine. Host-guest complexation by the molecular baskets is generally driven by dispersion interactions, C-H···π interactions of the guests with the aromatic walls of the cavity, and optimal cavity filling. Correlations between NMR-based structural data and binding affinities support that the complexed heterocyclic guests undergo additional polar C-O···C=O, N-H···π, and S···π interactions. The first crystal structure of a cavitand-based molecular basket is reported, providing precise information on the geometry and volume of the inner cavity in the solid state. Molecular dynamic (MD) simulations provided information on the size and conformational preorganization of the cavity in the presence of encapsulated guests. The strongest binding of heterocyclic guests, engaging in polar interactions with the host, was observed at a cavity filling volume of 63 ± 9%.     

Water-soluble supramolecular bowls formed by intra-clipping of resorcin[4]arene-based ligands with Pd(II) ions

Bowl-shaped superstructures have been constructed by intra-clipping of resorcin[4]arene derivatives with two equivalents of (en)Pd(NO3)2 in water. The binding phenomena of the aromatic carboxylates were proven to be both enthalpically and entropically favoured.     

Synthesis and photophysical studies of calix[4]arene-based binuclear platinum(II) complexes: probing metal-metal and ligand-ligand interactions

A series of calix[4]arene-based binuclear platinum(II) complexes, Pt2LCl2 (1, L = 5,11,17,23-tetra- tert-butyl-25,27-di[methoxy(4-phenyl)-(C;N;N)]-26,28-dihydroxycalix[4]arene, HC;N;N = 6-phenyl-2,2'-bipyridine), [Pt2L(mu-dppCn)](ClO4)2 (dppCn = bis(diphenylphosphino)-methane (2, n = 1), -ethane (3, n = 2), -propane (4, n = 3), and [Pt2L(PPh3)2](ClO4)2 (5), have been designed and synthesized in this work. Spectroscopic investigation demonstrates that p- tert-calix[4]arene is capable of assembling the two square-planar [(C;N;N)Pt(II)] units in a face-to-face manner, simultaneously suppressing intermolecular aggregation and increasing the solubility of the studied complexes. Facile replacement of the chloride ligand in 1 by the strongly sigma-donating ancillary phosphine ligands affords binuclear platinum(II) complexes with improved photophysical properties. All of the complexes are emissive both in the fluid/glassy solution and in the solid state, except for 1 in the solid state at room temperature. Moreover, the absorption and emission energies of the complexes are sensitive to the ancillary ligands. Varying the tethered phosphine auxiliaries from dppm (2) and dppe (3) to dppp (4) and PPh3 (5) modulates the intramolecular metal-metal (Pt...Pt) and ligand-ligand (pi-pi) distances, thereby leading to a switch of 3MMLCT and excimeric 3(pipi*) excited states to a common 3MLCT excited state.     

Nickel(II) and cobalt(II) complexes of 2,4-diaminothieno[2,3-d]-pyrimidines

Summary The reactions of methyl-2-amino-4-diethylamino thieno-[2,3-d]pyrimidine 6-carboxylate, methyl-2-amino-4-ethyl-phenylamine thieno-[2,3-d]pyrimidine-6-carboxylate) and methyl-2-amino, 4-morpholino-thieno-[2,3-d]pyrimidine-6-carboxylate with Ni^II and Co^II halides produced complexes of the general formula ML₂X₂ (where L is thieno pyrimidine and X is Cl or Br). The complexes were characterized by elemental analyses, conductivity and magnetic susceptibility measurements and spectroscopy. All of the complexes were found to have pseudotetrahedral structures with the metal coordinated through the N(1) site of the thieno-[2,3-d]-pyrimidine.     

Upper rim-functionalized calix[4]arene-based l-proline as organocatalyst for direct asymmetric aldol reactions in water and organic media

The synthesis of upper rim-functionalized calix[4]arene-based l-proline was described, and its catalytic efficiency as organocatalyst for the enantioselective aldol reaction in water was investigated. The results showed that the nature of the hydrophobic cavity of calixarene is critical for catalytic activity in water. The products of the reaction between various ketones and aldehydes with anti-configuration were obtained in high yields (up to 94%) with high diastereo- (up to 95:5 dr) and enantioselectivities (up to 80% ee).     

Tetrazolecalix[4]arenes as new ligands for palladium(II)

The synthesis of new calix[4]arenes bearing two or four tetrazole liganting groups at the upper rim is decribed. The structures of tetrakis-tetrazolecalix[4]arene and its palladium dichloride (2:2) complex are examined by X-ray crystallography.     

Selective detection of pyrophosphate by new tripodal amine calix[4]arene-based Cu(II) complexes using indicator displacement strategy

Mono- and dinuclear Cu(II) complexes of p-tert-butylcalix[4]arene (CuL1 and CuL2, respectively) were synthesized, and their anion recognition abilities were explored. Recognition is efficiently signaled through the displacement of pyrocatechol violet bound to the receptor. For CuL2, recognition selectivity is ascribed to the tuning of the distance between donor atoms of anion guests and their ability to encompass the Cu²⁺-Cu²⁺ distance within the cleft of CuL2. In addition, the preorganization of calix[4]arene in the cone conformation and steric hindrance of two bulky tripodal amine moieties are important factors in controlling the Cu²⁺-Cu²⁺ distance. These factors caused CuL2 to recognize pyrophosphate selectively with respect to other inorganic anions in 80/20 (v/v%) MeCN/H₂O solution buffered with 10 mM HEPES at pH 6.4.     

Unique trigonal prism encapsulated Ln complexes: a [Co(II)6Eu] and a [Co(II)6Dy] cage

The use of 2-amino-isobutyric acid in Co/Ln chemistry has led to the isolation of two unique [Co(II)(6)Ln(III)] 3d-4f metallic cages in which the Ln(III) centre (Ln = Eu, Dy) is encapsulated within a Co(II)(6) trigonal prism.     

Synthesis,spectroscopic characterization and X-ray single crystal structures of trans-bis[4-methoxyphenyl (3-methylbutyl) dithiophosphinato] nickel(II) and bis [4-methoxyphenyl (3-methylbutyl) dithiophosphinato]cobalt(II) complexes

Thionation of 3-methylbutylmagnesium bromide with Lawesson’s Reagent (LR) gave 4-methoxyphenyl (3-methylbutyl)dithiophosphinic acid (DTPA), and the latter was converted to the ammonium salt (NH₄L = Ammonium 4-methoxyphenyl (3-methylbutyl) dithiophosphinate). The complex, trans–bis[4-methoxyphenyl(3–methylbutyl) dithiophosphinato] nickel(II) [NiL₂], was prepared by the reaction of NH₄L with NiCl₂.6H₂O in EtOH. Bis [4-methoxyphenyl (3-methylbutyl) dithiophosphinato]cobalt(II) [(CoL₂)₂] was also prepared in the same way. The structures of the complexes have been characterized by elemental analysis, FTIR, ¹H, ¹³C, ³¹P NMR and X-ray diffraction. The single crystal X-ray structures of [NiL₂] and [(CoL₂)₂] show that the nickel complex is square planar while the cobalt counterpart has tetrahedral coordination with a dimeric structure. Bond lengths, angles, torsion angles and dihedral angles are correlated to the structures and also compared with the literature data on similar compounds.     

Synthesis and Crystal Structure of catena-Poly[bis-(benzimidazole)cobalt(II) μ-Phthalato]

1 INTRODUCTION Chemists have recognized that intermolecular inter- actions are the basis of functional properties for most molecular assembles, and detailed understan- ding of non-covalent chemistry is therefore funda- mental to interpreting and predicting the relation- ship between structure and function. Among intermo- lecular interactions, the π-π stacking between aro- matic rings is correlated with the electron transfer process in some biological systems[1], and the nature of π-π s…     

Magnetic behavior of tetrakis[4-(N-tert-butyl-N-oxylamino)pyridine]bis(isocyanato-N)cobalt(II) in frozen solution

A complex of cobalt(II)(OCN)(2) coordinated with four pyridines having a stable tert-butyl aminoxyl exhibited in frozen MTHF a slow magnetic relaxation for the reorientation of magnetization with activation barrier, Delta/k(B) = 50 K, and a hysteresis loop having a fast relaxation at 0 Oe below 2.5 K.     

Sensitized photoreduction of cobalt(II) and iron(II). Structural characterization of [Co(CO)(o-C6H4[PPh2]2)2]PF6

Triplet-state ketones readily sensitized the photoreduction of bis(acetyl-acetonato)cobalt(II) or CO_solv²⁺ under atmospheric pressure of carbon monoxide to give Co(CO)₄⁻. The low-valent cobalt could be trapped and isolated as phosphine-substituted metal carbonyl complexes. The crystal structure of one of the products, [Co(CO)(o-C₆H₄[PPh₂]₂)₂]PF₆ has been determined. It is orthorhombic, space group Pbca, Z = 8, with unit cell dimensions a 19.704(5), b 24.850(13), c 21.865(9) Å. Phosphine-substituted iron(0) carbonyl complexes have also been isolated from similar photoreductions of iron(II) species.     

Cucurbit[8]uril-based inclusion compounds containing iron(II), cobalt(III), and nickel(II) complexes with cyclam and cyclen as guest molecules: Synthesis and crystal structures

New inclusion compounds containing iron(II), cobalt(III), and nickel(II) complexes with the cyclic polyamine ligands cyclam and cyclen in the macrocyclic cavitand cucurbit[8]uril (CB[8]) were obtained: {trans-[Fe(Cyclam)(CO)(OCHO)]@CB[8]}Cl · 15H₂O, {cis-[Co(Cyclen)(H₂O)Cl]@CB[8]}Cl₂ · 20H₂O, and {cis-[Ni(Cyclen)(H₂O)Cl]@CB[8]}Cl · 12H₂O. According to X-ray diffraction data, the complexes are in the cavity of each CB[8] molecule. The complexes of the above molecular formulas were isolated in the solid state as supramolecular compounds with CB[8] and structurally characterized for the first time.