N-Heterocyclic carbene adducts of orthopalladated triarylphosphite complexes

Carbene adducts of orthopalladated triarylphosphite complexes have been synthesised and characterised. The structures of three of these complexes were determined by single-crystal X-ray analysis. The complexes are active in the Suzuki coupling of a range of aryl bromide substrates.     

Anomalous transport due to drift-wave turbulence

The anomalous transport of particles and thermal energy is analyzed for the electron and ion temperature gradient driven drift-wave turbulence. The entropy production from the anomalous flows is calculated. Approximate formulas for the fluctuation spectra are briefly compared with a microwave scattering experiment in a low beta tokamak.     

Synthesis of new chiral organosulfur donors with hydrogen bonding functionality and their first charge transfer salts

The syntheses of a range of enantiopure organosulfur donors with hydrogen bonding groups are described including TTF related materials with two, four, six and eight hydroxyl groups and multiple stereogenic centres and a pair of chiral N-substituted BEDT-TTF acetamides. Three charge transfer salts of enantiopure poly-hydroxy-substituted donors are reported, including a 4:1 salt with the meso stereoisomer of the dinuclear [Fe₂(oxalate)₅]⁴⁻ anion in which both cation and anion have chiral components linked together by hydrogen bonding, and a semiconducting salt with triiodide.     

Characterization of prenylated xanthones and flavanones by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

Reversed-phase liquid chromatography with atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) in the positive-ion mode was utilized to analyze crude ether extracts from the root bark of Maclura pomifera, a tree known to have a high content of prenylated xanthones and flavanones. Identification of three xanthones and two flavanones was based on their unique mass spectra. Under optimum conditions peaks corresponding to the [MH](+) ion and characteristic fragments for each compound were observed. (1)H NMR data were used to confirm the identities of two xanthones that had the same molecular mass and similar fragmentation patterns. Fragmentation of the analytes was achieved by application of an electrostatic potential at the entrance of the single quadrupole mass spectrometer. The optimum voltage for fragmentation was found to be related to the class of compounds analyzed and, within each class, to be dependent on the structure of the prenyl moiety. Collision-induced pathways consistent with precedent literature describing the MS characterization of similar compounds and with the observed fragmentation patterns are tentatively proposed.     

Theoretical and experimental analysis of the antioxidant features of diarylhydrazones

Structural and energetic features of a series of 15 diarylhydrazone derivatives were studied via density functional theory (DFT) in order to identify the key features that most likely contribute to their antioxidant effect. Theoretical calculations were carried out at the B3LYP/6-31G(d,p) level. The calculated physicochemical parameters included the ionization potential, N-H dissociation enthalpy, proton affinity, HOMO/LUMO energies, and the band gaps of the most stable conformation of the compounds. To assess the contribution of these factors to the in vitro activity, the compounds were synthesized and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), and peroxyl (ORAC assay) radicals. The experimental radical scavenging data of the compounds have been then plotted against the physicochemical characteristics and based on the obtained fits conclusions have been drawn regarding the relative importance of the respective factors.     

Cycloaddition of Cyclopentadiene to 3-Deoxy-1,2:5,6-di-O-isopropylidene-alpha-D-erythro-hex-3-enofuranose. Synthesis and Representative Chemistry of 1,6-Anhydro-2,3-dideoxy-beta-D-glycero-hex-2-enopyran-4-ulose ("Isolevoglucosenone")

Treatment of D-glucose-derived alkene 4 with cyclopentadiene in the presence of a Lewis acid results in the formation of cycloaddition products 8-11. Evidence is presented to show that these 1,6-anhydro sugar-cyclopentadiene adducts do not arise from rearrangement of 4 to isolevoglucosenone (5) followed by cycloaddition but are the result of Lewis acid-catalyzed rearrangement of alkene 4 to acyclic dienophile 12 followed by addition of cyclopentadiene. Major cycloadduct 8 has been utilized as a source of the enantiomerically pure carbocycles 14-25 by manipulation of the alkene and ketone functions and cleavage of the 1,6-anhydro bridge. In the absence of diene, alkene 4 undergoes rearrangement to enone 5 in 32% yield. Reaction of 5 with several dienes results only in the formation of "bottom-face" adducts 10,11, 28, and 29, and conjugate addition of either HN(3) or Me(3)COOH is found to be completely stereoselective to afford 30 and 31, respectively. Subsequent manipulation of azide 30 leads to precursors of several naturally occurring 2-amino-2,3-dideoxy sugars.     

Synthesis and characterisation of benzyl phosphino-thioether and -thiolato Pd(II) complexes and their applications in Suzuki coupling reactions

The synthesis of the benzyl phosphinothioether derivatives Ph(2)PCH(2)CH(Et)SR and their corresponding palladium complexes are reported, where R = CH(2)Ph, R = CH(2)-3,5-Me-C(6)H(3) and R = 1-CH(2)C(10)H(7)(5). Crystallographic data obtained for the complexes Pd(3)Cl(2) and Pd(4)Cl(2) show intra- and inter-molecular pi-pi interactions between the aromatic rings on the P and S substituents, and NOE experiments for Pd(4)Cl(2) show that these interactions persist in solution. The performance of the phosphinothioether palladium complexes in aryl-aryl cross-coupling reactions is compared with that of the corresponding complex of the parent phosphinothiolato ligand Ph(2)PCH(2)CH(Et)S(-)(1). High turnover numbers up to 2000000 are reported for the coupling of bromobenzene, using the palladium dimer [Pd(1)I](2) as the catalyst precursor. Kinetic studies show a linear dependence of the reaction on catalyst loading. The effect of other variables on the cross-coupling reaction, such as temperature, solvent and base, is also reported.