Aza-capped cyclodextrins for intra-cavity metal complexation.

Aza-capped, methylated cyclodextrins (CDs) were obtained in high yields by reacting the soft nitrogen nucleophile 2-nitrobenzenesulfonamide with either A,B-dimesylated CDs in basic media or their diol analogues under Mitsunobu reaction conditions followed by deprotection with thiophenol. A methyl pyridine substituent was grafted on the N atom of these secondary amines. When built on an α-CD scaffold, the resulting tertiary amine no longer undergoes nitrogen inversion at room temperature and behaves as a confining ligand, opening the way to intra-cavity metal complexation and promoting the formation of supramolecular helices.

Vibrational dynamics (IR, Raman, NRVS) and a DFT study of a new antitumor tetranuclearstannoxane cluster, Sn(iv)-oxo-{di-o-vanillin} dimethyl dichloride.

The vibrational dynamics of a newly synthesized tetrastannoxane was characterized with a combination of experimental (Raman, IR and tin-based nuclear resonance vibrational spectroscopy) and computational (DFT/B3LYP) methods, with an emphasis on the vibrations of the tin sites. The cytotoxic activity revealed a significant regression selectively against the human pancreatic cell lines.

Out-of-equilibrium dynamics of photoexcited spin-state concentration waves.

The spin crossover compound [FeIIH2L2-Me][PF6]2 presents a two-step phase transition. In the intermediate phase, a spin state concentration wave (SSCW) appears resulting from a symmetry breaking (cell doubling) associated with a long-range order of alternating high and low spin molecular states. By combining time-resolved optical and X-ray diffraction measurements on a single crystal, we study how such a system responds to femtosecond laser excitation and we follow in real time the erasing and rewriting of the SSCW.

Aperiodic spin state ordering of bistable molecules and its photoinduced erasing.

We describe a novel type of ordering phenomenon associated with the incommensurate occupational modulation of bistable molecular magnetic state in a spin-crossover material. This unusual type of aperiodicity resulting from the ordering of multistable electronic states opens new possibilities for addressing such materials by light. Here we show that light can switch the crystal from four- to three-dimensional periodic structure. Mixing aperiodicity, multistability, and photoinduced phenomenà opens new perspectives for directing complex order and function in material science.

Discovery of an intermediate phase in bis-thiourea pyridinium chloride inclusion compound.

This paper reports the occurrence of a new phase for bis-thiourea pyridinium chloride inclusion compound, which is intermediate to the high- and low-temperature ones already reported. The structure of the intermediate phase was determined by the x-ray diffraction and the following sequence of space groups was obtained: Cmcm-->(237 K)Cmc2(1)-->(206 K)Pbca. The triplication of the lattice a parameter in the intermediate phase was observed. Detailed investigations of its phase transitions were performed by differential scanning calorimetry, x-ray diffraction, and dielectric spectroscopy methods. The phase transition at T(1)=237 K is continuous while at T(2)=206 K is discontinuous. Both phase transitions have been classified as of order-disorder type. The high- and low-temperature phases are nonpolar in contrast to the intermediate phase, for which we could not found ferroelectric ordering.

Structural and dynamical aspects of the phase transition in the new thiourea thiazolium bromide inclusion compound.

A new thiourea thiazolium bromide inclusion compound is presented here. Detailed investigations of its phase transition were performed by differential scanning calorimetry, x-ray diffraction, and dielectric and nuclear magnetic resonance spectroscopy methods, completed by calculation of the steric hindrances for molecular reorientations and simulations of the second moment of the nuclear magnetic resonance line by the Monte Carlo method. A second order ferrielectric structural phase transition has been detected at 190.5 K as thiazolium cations collectively reorient inside channels. The dynamics is discussed in terms of inequivalent energy barriers associated with cation rotation as the symmetry breaking occurs. Oscillations of thiourea molecules and NH(2) groups have been also observed.

Phosphole-containing pi-conjugated systems: from model molecules to polymer films on electrodes.

Two series of 2,5-dipyridyl- and 2,5-dithienylphosphole derivatives containing sigma3- or sigma4-P atoms were prepared, and their optical (UV/Vis absorption, fluorescence spectra) and electrochemical properties were systematically evaluated. These physical properties depend mainly on the natures of the 2,5-substituents and of the phosphorus moiety, and they revealed that these compounds contain extended pi-conjugated systems. Structure-property relationships were established on the basis of these experimental data and ab initio calculations on the parent molecules. The limited aromatic character and low-lying LUMO of the phosphole ring appear to be crucial for achieving a highly delocalised pi system. Electrooxidation of 2,5-dithienylphosphole derivatives affords electroactive films with low optical band gaps. As observed for the corresponding monomers, the optical and electrochemical properties of the polymers can be varied over a wide range by modifying the nature of the phosphorus moiety.

Theoretical, thermodynamic, spectroscopic, and structural studies of the consequences of one-electron oxidation on the Fe-X bonds in 17- and 18-electron Cp*Fe(dppe)X complexes (X = F, Cl, Br, I, H, CH3).

The compounds Cp*Fe(dppe)X ([Fe]X) and the corresponding cation radicals [Fe*]X*+ are available for the series X = F, Cl, Br, I, H, CH3. This has allowed for a detailed investigation of the dependence of the nature of Fe-X bonding on the identity of X and the oxidation state (charge) of the complex. Cyclic voltammetry demonstrates that the electrode potentials for the [Fe]X0/+ couples decrease in the order I > Br > Cl > H > F > CH3. An "inverse halide order" is seen, in which the most electronegative X leads to the most easily oxidized complex. This suggests that F is the best donor among the halides. The halide trend is also reflected in NMR spectroscopic data. Mössbauer spectroscopy data also suggest that the F ligand is a strong donor (relative to H and CH3) in [Fe*]X*+. DFT calculations on CpFe(dpe)X ([Fe]X) model complexes nicely reproduce the trend in the electrode potentials for the [Fe*]X0/+ couples. Analysis of the theoretical data within the halogen series indicates that the energy of the [Fe]X HOMO does not correlate with the extent of its Fe(d(pi))-X(p(pi)) antibonding character, which varies in the order I > Br > Cl > F, but rather depends on the destabilizing electrostatic effect caused by X. This effect varies in the order F > Cl > Br > I. A thermochemical cycle that incorporates the [Fe*]X0/+ and [Fe*]0/+ electrode potentials was used to investigate the effect of the oxidation state of the complex on the homolytic bond dissociation energy (BDEhom), defined for the processes Fe-X --> Fe* + X* and Fe-X*+ --> Fe*+ + X*. For all X, it was found that a one-electron oxidation leads to a weakening of the Fe-X bond. This trend was reproduced by the DFT calculations. On the other hand, IR nu(Fe-X) spectroscopy data showed an increase in the stretching frequencies for X = H and Cl upon oxidation. X-ray crystallographic data showed a shortening of the Fe-Cl bond upon oxidation. The trends in IR and Fe-Cl bond distances were reproduced in the DFT calculations. The combined data therefore suggest that oxidation leads to weaker, but shorter, Fe-X bonds. A second thermochemical cycle was applied to investigate the effect of the one-electron oxidation on the heterolytic bond dissociation energies (BDEhet), defined for the processes Fe-X --> Fe+ + X- and Fe-X*+ --> Fe2+ + X-. In this case, the oxidation led to bond strengthening in all cases. The computed BDE values have been analyzed within Ziegler's transition state methodology and decomposed into two components, one electrostatic and one covalent, describing the interaction between the unrelaxed fragments. In all the computed BDEhom and BDEhet values of the [Fe]X models the electrostatic component is important. This helps to understand their respective variations upon oxidation.

N-(tert-butoxycarbonyl)-N-[4-(dimethylazaniumylidene)-1,4-dihydropyridin-1-ylsulfonyl]azanide: a new sulfamyolating agent. Structure and reactivity toward amines.

[structure: see text] Synthesis, structure, and reactivity toward amines of the new sulfamoylating reagent 2 are described. Compound 2 allowed sulfamoylation of amines under very mild conditions to give sulfamide derivatives in good yields.

A very short synthesis of steroids from 1,3-butadiene and benzocyclobutenes.

Lewis acid mediated addition of 1,8-bis(trimethylsilyl)octa-2,6-diene (BISTRO) 1 to succinic anhydride led to spirolactone 2 [(+/-)-6,9-divinyl-1-oxaspiro[4.4]nonan-2-one]. Methoxycarbonylation followed by stereoselective alkylation by various benzocyclobutenes afforded the substituted benzocyclobutene steroid precursors 5. Thermolysis of 5 gave rise to steroids (+/-)-6 with a trans-anti-cis configuration in five steps and in a highly stereoselective manner. Modifications of the sequence allowed the preparation of steroids (+/-)-11 with trans-anti-trans configuration.

Conformations of allylic fluorides and stereoselectivities of their diels-alder cycloadditions.

The preparations of new allylic fluorides from the corresponding alcohols are reported. Conformational analysis is achieved by comparison of experimental NMR measurements with theoretical (B3LYP) calculations of relative energies of conformers and J(H,H) and J(H,F) coupling constants. The Diels-Alder reactions of allylic fluorides are investigated experimentally and theoretically. The stereoselectivities of the reactions were determined by NMR analysis and, in one case, by X-ray crystallography. Theoretical predictions of stereoselectivity based upon transition state modeling provided good agreement with experiment. Theoretical models for allylic fluorides and transition state conformations are reported.

Activation of the dienophilicity of indoles in normal electron demand [4 + 2] cycloadditions under high pressure.

[reaction: see Text] Activation by either high pressure or a combination of Lewis acid catalysis and high pressure allows indole derivatives to behave as dienophiles in [4 + 2] cycloaddition reactions under mild conditions. The biactivation mode has the highest impact on the stereoselectivity of the reaction. The cycloadducts resulting from these reactions are characterized by boat-shape conformations that bear well-defined orthogonal planes.

Bis

The geometry about the Ru atom in the title compound, [Ru(C(9)H(9)N)(2)(C(92)H(108)N(4)O(24))], is approximately tetragonal and the porphyrin ring is nearly planar, while the C-N-R angles [169.3 (3) and 163.9 (3) degrees ] of the isocyanide ligands in the complex are different from the value of 180 degrees expected in the free ligand.

First asymmetric synthesis of a 6-alkoxy-5,6-dihydro-1,3-oxazine: a promising enantioselective route to beta-amido aldehydes

[reaction: see text] The 1,3-oxazine route to enantiopure beta-amido aldehydes was investigated. Heterocycloaddition of the N-acyl imine 1 with (R)-O-vinylpantolactone provided the stable dihydroxazine 4c. High diastereocontrols were observed when using Yb(fod)3-catalyzed or SnCl4-mediated conditions, thus leading after quantitative hydrolysis to (R)-N-benzoyl-3-phenylpropanal with >98% ee.

A novel leishmanicidal labdane from Polyalthia macropoda.

A new diterpene, (4S,9R,10R) methyl 18-carboxy-labda-8,13(E)-diene-15-oate has been obtained from the stem barks of Polyalthia macropoda (Annonaceae). This labdanic derivative was identified on the basis of spectroscopic data and is biologically active against the promastigote Leishmania donovani donovani.