Design, synthesis, and applications of potential substitutes of t-Bu-phosphinooxazoline in Pd-catalyzed asymmetric transformations and their use for the improvement of the enantioselectivity in the Pd-catalyzed allylation reaction of fluorinated allyl enol carbonates

The design, synthesis, and applications of potential substitutes of t-Bu-PHOX in asymmetric catalysis is reported. The design relies on the incorporation of geminal substituents at C5 in combination with a substituent at C4 other than t-butyl (i-Pr, i-Bu, or s-Bu). Most of these new members of the PHOX ligand family behave similarly in terms of stereoinduction to t-Bu-PHOX in three palladium-catalyzed asymmetric transformations. Electronically modified ligands were also prepared and used to improve the enantioselectivity in the Pd-catalyzed allylation reaction of fluorinated allyl enol carbonates.     

Novel heterometal-organic complexes as first single source precursors for up-converting NaY(Ln)F4 (Ln = Yb, Er, Tm) nanomaterials

First heterometal-organic single source precursors for NaYF(4) nanomaterials as a host matrix for up-conversion emission are reported. These novel heterobimetallic derivatives NaY(TFA)(4)(diglyme) (1), [Na(triglyme)(2)][Y(2)(TFA)(7)(THF)(2)] (2) and Na(2)Y(TFA)(5)(tetraglyme) (3) (TFA = trifluoroacetate), which were fully characterized by elemental analysis, FT-IR and (1)H NMR spectroscopy, TG-DTA data as well as single crystal X-ray structures, are advantageous in terms of being anhydrous and having lower decomposition temperatures in comparison to the homometallic precursor Y(TFA)(3)(H(2)O)(3). In addition, they also contain chelating glyme ligands, which act as capping reagents during decomposition to control the NaYF(4) particle size and render them monodisperse in organic solvents. On decomposition in 1-octadecene, the molecular derivatives 1 and 3 are converted, in the absence of any surfactant or capping reagent, to cubic NaYF(4) nanocrystals at significantly lower temperatures (below 250 °C). At higher temperature, a mixture of the cubic and hexagonal phases was obtained, the relative ratio of the two phases depending on the reaction temperature. A pure hexagonal phase, which is many folds more efficient for UC emission than the cubic phase, was obtained by calcining nanocrystals of mixed phase at 400 °C. In order to co-dope this host matrix with up-converting lanthanide cations, analogous complexes NaLn(TFA)(4)(diglyme) [Ln = Er (4), Tm (5), Yb (6)] and Na(2)Ln(TFA)(5)(tetraglyme) [Ln = Er (7), Yb (8)] were also prepared and characterized. The decomposition in 1-octadecene of suitable combinations and appropriate molar ratios of these yttrium, ytterbium and erbium/thulium derivatives gave cubic and/or hexagonal NaYF(4): Yb(3+), Er(3+)/Tm(3+) nanocrystals (NCs) capped by diglyme or tetraglyme ligands, which were characterized by IR, TG-DTA data, EDX analysis and TEM studies. Surface modification of these NCs by ligand exchange reactions with poly acrylic acid (PAA) and polyethyleneglycol (PEG) diacid 600 was also carried out to render them water soluble. The THF solutions of suitable combinations of the diglyme derivatives were also used to elaborate the thin films of NaYF(4):Yb(3+), Er(3+)/Tm(3+) on a glass or Si wafer substrate by spin coating. The multicolour up-conversion fluorescence was successfully realized in the Yb(3+)/Er(3+) (green/red) and Yb(3+)/Tm(3+) (blue/violet) co-doped NaYF(4) nanoparticles and thin films, which demonstrates that they are promising UC nanophosphors of immense practical interest. The up-conversion excitation pathways for the Er(3+)/Yb(3+) and Tm(3+)/Yb(3+) co-doped materials are discussed.     

Liquid-crystalline zinc(II) and iron(II) alkyltriazoles one-dimensional coordination polymers

Several series of unidimensional coordination polymers of formula [Zn(C(n)H(2n+1)trz)(3)](Cl)(2)·xH(2)O (n = 18, 16, 13, 11, 10, trz = 4-substituted-1,2,4-triazole), [Zn(C(18)H(37)trz)(3)](ptol)(2)·xH(2)O, [Fe(C(n)H(2n+1)trz)(3)](X)(2)·xH(2)O (n = 18, 16, 13, 10; X = Cl(-) or ptol(-), where ptol(-) = p-tolylsulfonate anion), and [Fe(C(18)H(37)trz)(3)](X)(2)·xH(2)O (X = C(8)H(17)PhSO(3)(-) and C(8)H(17)SO(3)(-)) are reported with their thermal, structural, and magnetic properties. Most of these materials exhibit thermotropic lamellar mesophases at temperatures as low as 410 K, as confirmed by textures observed by polarized optical microscopy. The corresponding phase diagrams deduced by differential scanning calorimetry are also reported. All iron-containing materials present a spin crossover phenomenon that occurs at temperatures ranging from 242 to 360 K, only slightly below the mesophase temperature domain, and remains complete and cooperative, even for the longer alkyl substituents. The use of stable diamagnetic Zn(II) analogues proves to be very useful to characterize the comparatively less stable and less crystalline Fe(II) analogues.     

Hyperbranched Polyether Polyols with Liquid Crystalline Properties

The attachment of mesogens as end groups to hyperbranched polyglycerol (degree of polymerization 22–45; see schematic representation, the rigid mesogens are shown as rods and the flexible alkyl chains as lines) leads to liquid crystalline polymers with narrow polydispersity, whose liquid crystalline behavior is induced by the mesogenic end groups only.     

Efficient preparation,uses, and recycling of a polymer-bound sulfonylhydrazide scavenger

Polymer-bound sulfonylhydrazide was prepared from commercial sulfonic acid resin through a straightforward, one-step synthetic route avoiding chlorosulfonic intermediates. The simplex self-directing optimization method was used to determine rapidly the ideal operating conditions under microwave irradiation. Polymer-bound sulfonylhydrazide has found an application as scavenging agent in winemaking therefore, this clean preparative approach is expected to be more acceptable by winemakers. An efficient recycling protocol of the used supports has also been established.     

Miscible blends prepared from two crystalline polymers

Differential scanning calorimetry was used to determine the miscibility behavior of several polyester/Saran blends, the two polymers forming these blends being semicrystalline. It was found that Saran is miscible with polycaprolactone (PCL), polyvalerolactone, poly(butylene adipate), and poly(hexamethylene sebacate) since a single glass transition temperature T_g was observed at each composition. However, immiscibility was found between Saran and poly(ethylene adipate), poly-(ethylene succinate), poly(β-propiolactone), and poly(α-methyl-α-n-propyl-β-propiolactone) since two T_g's were recorded at several compositions. Blends were then obtained containing, over a wide range of composition, a miscible amorphous phase and two different types of crystals. From melting-point depression data on PCL and Saran crystals, thermodynamic interaction parameters χ were calculated and found to be different for PCL-rich blends and for Saran-rich blends. This result suggests a variation of χ with composition. Saran is a polymer which does not contain α-hydrogens and its miscibility with polyesters may result from a β-hydrogen bonding interaction or a C?O/C? Cl dipole-dipole interaction.     

Homologie cyclique,principe de Selberg et pseudo-coefficient

Sans résuméOblatum 8-VII-1992 & 14-VII-1993To Armand Borel     

Interfacial microgels formed by oppositely charged polyelectrolytes and surfactants. 1. Influence of polyelectrolyte molecular weight

The synergistic adsorption and complexation of polystyrene sulfonate, PSS (a highly charged anionic polyelectrolyte), and dodecyltrimethylammonium bromide, C12TAB (a cationic surfactant), at the air-water interface can lead to interfacial gels that strongly influence foam-film drainage and stability. The formation and characteristics of these gels have been studied as a function of PSS molecular weight by combining surface tension, ellipsometry, and foam-film drainage experiments. Simultaneously the solution electromotive force has been measured to track the polymer-surfactant interactions in the bulk solution. It has been found that there is a critical molecular weight for surface gelation as well as for bulk precipitation and aggregation. Furthermore, we show that for the lowest molecular weights, PSS adsorbs with C12TAB in compact layers at the air-water interface. In particular, for mixtures of C12TAB with the monomer compound of the PSS repeat unit (e.g. Mw = 208), interfacial complexation is found to be similar to that of catanionic mixtures (mixtures of surfactants of opposite charge).     

Binuclear manganese compounds of potential biological significance. Part 2. Mechanistic study of hydrogen peroxide disproportionation by dimanganese complexes: the two oxygen atoms of the peroxide end up in a dioxo intermediate

The dimanganese(II,II) complexes 1a [Mn(2)(L)(OAc)(2)(CH(3)OH)](ClO(4)) and 1b [Mn(2)(L)(OBz)(2)(H(2)O)](ClO(4)), where HL is the unsymmetrical phenol ligand 2-(bis-(2-pyridylmethyl)aminomethyl)-6-((2-pyridylmethyl)(benzyl)aminomethyl)-4-methylphenol, react with hydrogen peroxide in acetonitrile solution. The disproportionation reaction was monitored by electrospray ionization mass spectrometry (ESI-MS) and EPR and UV-visible spectroscopies. Extensive EPR studies have shown that a species (2) exhibiting a 16-line spectrum at g approximately 2 persists during catalysis. ESI-MS experiments conducted similarly during catalysis associate 2a with a peak at 729 (791 for 2b) corresponding to the formula [Mn(III)Mn(IV)(L)(O)(2)(OAc)](+) ([Mn(III)Mn(IV)(L)(O)(2)(OBz)](+) for 2b). At the end of the reaction, it is partly replaced by a species (3) possessing a broad unfeatured signal at g approximately 2. ESI-MS associates 3a with a peak at 713 (775 for 3b) corresponding to the formula [Mn(II)Mn(III)(L)(O)(OAc)](+) ([Mn(II)Mn(III)(L)(O)(OBz)](+) for 3b). In the presence of H(2)(18)O, these two peaks move to 733 and to 715 indicating the presence of two and one oxo ligands, respectively. When H(2)(18)O(2) is used, 2a and 3a are labeled showing that the oxo ligands come from H(2)O(2). Interestingly, when an equimolar mixture of H(2)O(2) and H(2)(18)O(2) is used, only unlabeled and doubly labeled 2a/b are formed, showing that its two oxo ligands come from the same H(2)O(2) molecule. All these experiments lead to attribute the formula [Mn(III)Mn(IV)(L)(O)(2)(OAc)](+) to 2a and to 3a the formula [Mn(II)Mn(III)(L)(O)(OAc)](+). Freeze-quench/EPR experiments revealed that 2a appears at 500 ms and that another species with a 6-line spectrum is formed transiently at ca. 100 ms. 2a was prepared by reaction of 1a with tert-butyl hydroperoxide as shown by EPR and UV-visible spectroscopies and ESI-MS experiments. Its structure was studied by X-ray absorption experiments which revealed the presence of two or three O atoms at 1.87 A and three or two N/O atoms at 2.14 A. In addition one N atom was found at a longer distance (2.3 A) and one Mn at 2.63 A. 2a can be one-electron oxidized at E(1/2) = 0.91 V(NHE) (DeltaE(1/2) = 0.08 V) leading to its Mn(IV)Mn(IV) analogue. The formation of 2a from 1a was monitored by UV-visible and X-ray absorption spectroscopies. Both concur to show that an intermediate Mn(II)Mn(III) species, resembling 4a [Mn(2)(L)(OAc)(2)(H(2)O)](ClO(4))(2), the one-electron-oxidized form of 1a, is formed initially and transforms into 2a. The structures of the active intermediates 2 and 3 are discussed in light of their spectroscopic properties, and potential mechanisms are considered and discussed in the context of the biological reaction.