Preparation and properties of dinitrogen complexes of molybdenum and tungsten with trimethylphosphine as coligand : III. Synthesis and properties of cis-[W(N2)2(PMe3)4], trans-[W(C2H4)2(PMe3)4] and [M(N2)(PMe3)5] (M = Mo,W). The crystal and molecular structure of [Mo(N2)(PMe3)5]

The reduction of [WCl₄(PMe₃)₃] with dispersed sodium, under dinitrogen, gives cis-[W(N₂)₂(PMe₃)₄], while under ethylene trans-[W(C₂H₄)₂(PMe₃)₄] is obtained. The ethylene complex can also be prepared by displacement of the dinitrogen molecules in cis-[W(N₂)₂(PMe₃)₄] by ethylene at room temperature and pressure. Interaction of cis-[M(N₂)₂(PMe₃)₄] complexes (M = Mo, W), with PMe₃, under helium or argon, yields [M(N₂)(PMe₃)₅]. The molybdenum complex crystallizes in the orthorhombic space group Pnma, with a 22.063(6), b 12.106(4), c 9.745(4) Å. The Mo—P distance trans to the dinitrogen ligand (2.483(7) Å) is slightly longer than the average of the other four Mo—P bonds (2.460(5) Å).     

Enantioseparations of polyhalogenated 4,4’-bipyridines on polysaccharide-based chiral stationary phases and molecular dynamics simulations of selector–selectand interactions

2’-(4-Pyridyl)- and 2’-(4-hydroxyphenyl)-TCIBPs (TCIBP = 3,3’,5,5’-tetrachloro-2-iodo-4,4’-bipyridyl) are chiral compounds that showed interesting inhibition activity against transthyretin fibrillation in vitro. We became interested in their enantioseparation since we noticed that the M-stereoisomer is more effective than the P-enantiomer. Based thereon, we recently reported the enantioseparation of 2’-substituted TCIBP derivatives with amylose-based chiral columns. Following this study, herein we describe the comparative enantioseparation of both 2’-(4-pyridyl)- and 2’-(4-hydroxyphenyl)-TCIBPs on four cellulose phenylcarbamate-based chiral columns aiming to explore the effect of the polymer backbone, as well as the nature and position of substituents on the side groups on the enantioseparability of these compounds. In the frame of this project, the impact of subtle variations of analyte and polysaccharide structures, and mobile phase (MP) polarity on retention and selectivity was evaluated. The effect of temperature on retention and selectivity was also considered, and overall thermodynamic parameters associated with the analyte adsorption onto the CSP surface were derived from van ’t Hoff plots. Interesting cases of enantiomer elution order (EEO) reversal were observed. In particular, the EEO was shown to be dependent on polysaccharide backbone, the elution sequence of the two analytes being P-M and M-P on cellulose and amylose tris(3,5-dimethylphenylcarbamate), respectively. In this regard, a theoretical investigation based on molecular dynamics (MD) simulations was performed by using amylose and cellulose tris(3,5-dimethylphenylcarbamate) nonamers as virtual models of the polysaccharide-based selectors. This exploration at the molecular level shed light on the origin of the enantiodiscrimination processes.     

Neutral solvent/crown ether interactions 3. Reorientation of the hydrogen bonds in the low temperature (−150°C) structure of 18-crown-6·2(CH3NO2)

The title complex was crystallized from a saturated solution of 18-crown-6 in nitromethane at 5°C and cooled to –150°C prior to X-ray diffraction data collection. At –150° C 18-crown-6·2(CH₃NO₂) is monoclinic,P2₁/_n witha=9.290(2),b=7.864(6),c=13.627(8) Å, =1000.84(4)° andD _calc=1.31 g cm^–3 for Z=2. Leastsquares refinement using 1521 independent observed reflections [F _o5(F _o)] led to a final conventionalR value of 0.041. The complex at –150°C is isostructural with its room temperature structure with the exception of the orientation of the methyl hydrogen atoms and their crown ether oxygen interactions. The methyl group hydrogen atoms were fully refined isotropically. The crown ether resides around a center of inversion and hasD _3d symmetry. There is one methyl hydrogen...crown interaction at 2.35(3) Å, one apparently bifurcated hydrogen bond utilizing a second methyl hydrogen atom (2.55(3), 2.65(3) Å) and the third hydrogen atom is actually directed away from the crown ring (closest H...O contact=2.67(3) Å). Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82048 (5 pages).For part 2, see reference [24].     

Synthesis of 4-(4-Alkyl-2-morpholinyl)indoles

N-substituted 4-(2-morpholinyl)indoles were prepared from 1-(t-butoxycarbonyl)-4-acetylindole (7) which was itself prepared from 4-cyanoindole. Bromination of ketone 7, followed by reaction with amines and subsequent sodium borohydride reduction, gave amino alcohols. These were converted to α-chloro amides that were cyclized to lactams. Lithium aluminum hydride reduction served both to remove the t-BOC protecting group and to reduce the lactams to the 4-(2-morpholinyl) indoles.     

The effect of fluctuations on emission spectra: practical distinctions between raman and fluorescence spectra

By the use of stochastic theory it is clearly shown that two types of emission should to fluctuations such as would occur during interactions with their environment are resonantly driven by light. In our approach the electromagnetic field is treated in a classical manner and decay is introduced by a Wigner-Weisskopfansatz. The two types of emission should occur for a three-level system and relaxation to other levels is not involved in the mechanism. Also included is a discussion of operational definitions of fluorescence (and other spontaneous emissions) and of the relationship between absorption and scattering in terms of dephasing or T₂ processes, especially as this relates to conventional emission phenomena.     

Study and characterization of virgin and recycled LDPE/PP blends

Recycling of mixed plastic wastes composed of low-density polyethylene (LDPE) matrix and polypropylene (PP) was carried out by compounding using single-screw or twin-screw extruders. Blends of virgin polymers have been prepared to compare mechanical properties of both virgin and regenerated materials. First, a model composition of virgin LDPE/PP blend was prepared to study the effect of process parameters and that of different types of compatibilizers. Second, the results were applied to plastic wastes coming from industrial post-consumer plastic wastes. By adding compatibilizing agents such as ethylene-propylene-diene monomer, ethylene-propylene monomer, or PE-g-(2-methyl-1,3-butadiene) graft copolymer, elongation at break and impact strength were improved for all blends. The effect of these various copolymers is quite different and is in relation with their chemical structure. The recycled blends exhibit suitable properties leading to applications that require good mechanical properties.     

A new chiral Rh(II) catalyst for enantioselective [2 + 1]-cycloaddition. mechanistic implications and applications

A novel chiral Rh(II) catalyst (1) is introduced for the [2 + 1]-cycloaddition of ethyl diazoacetate to terminal acetylenes and olefins with high enantioselectivity. The catalyst 1 consists of one acetate bridging group and three mono-N-triflyldiphenylimidazoline-2-one bidentate ligands (DPTI) spanning the Rh(II)-Rh(II) metallic center in a structure that was determined by single-crystal X-ray diffraction analysis. A rational mechanism is advanced that provides a straightforward explanation for the enantioselectivity and absolute stereochemical course of the [2 + 1]-cycloaddition reactions. A key element in this explanation is the cleavage of one of the Rh-O bonds of the bridging acetate group in the intermediate Rh-carbene complex to form a new pentacoordinate Rh carbene complex (formally 1.5 valent Rh) that can undergo [2 + 2]-cycloaddition with the C-C pi-bond of the acetylenic or olefinic substrate. Reductive elimination of the resulting adduct affords the cyclopropene or cyclopropane product. The C2-symmetry of the two DPTI ligands orthogonal to the bridging acetate also contributes to the high observed enantioselectivity and mechanistic clarity. The catalyst 1, which functions effectively at 0.5 mol %, can be recovered efficiently for reuse. Its ready availability, robustness, and effectiveness suggest it as a useful addition to the list of practical chiral Rh(II) catalysts for synthesis.     

Superstructures of donor packing arrangements in a series of molecular charge transfer salts

Three conducting BEDT-TTF charge-transfer salts with tris(oxalato)metallate anions have unit cells containing both[small alpha] and [small beta][double prime] donor packing motifs.     

N-halogeno-compounds. Part 9 [1]. Azoxy- and azo-arenes derived from 4-(dichloroamino)tetrafluoropyridine; crystal structure of trans-2,3,5,6-tetrafluoro-4-(2,4,6-trimethylphenyl-onn-azoxy)pyridine

The nitrosoarenes ArNO (Ar = C₆H₅, 2-MeC₆H₄, 2,4,6- Me₃C₆H₂ and C₆F₅) have been condensed with 4-(dichloroamino)- tetrafluoropyridine to provide the azoxy-compounds py_FN$\text{N}\text{+}$($\text{N}\text{-}$)Ar (py_F = 2,3,5,6-tetrafluoro-4-pyridyl); de-oxygenation of the first three with triphenylphosphine or triethyl phosphite gave the corresponding azo-compounds, and the reverse reaction was achieved in the case of py_FNNC₆H₂Me₃-2,4,6 using peroxytrifluoroacetic acid. Thermolysis of 4-azidotetrafluoropyridine in the presence of pentafluoronitrosobenzene provided the perfluorinated azoxy-compound py_FN$\text{N}\text{+}$($\text{O}\text{-}$)C₆F₅. X-Ray methods have been used to determine the molecular geometry of py_FN$\text{N}\text{+}$($\text{O}\text{-}$)C₆H₂Me₃-2,4,6.