New emissive fac-tricarbonylchlorobis(ligand)rhenium(I) complexes prepared from pyridine/thiophene hybrid ligands

Stille coupling between tributyl-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)-stannane and 4-bromopyridine resulted in the preparation of the new pyridine/thiophene hybrid ligand 4-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)-pyridine [4-py-EDOT] (1). Reaction of 1, 4-thiophen-2-yl-pyridine (2), or 4-[2,2^′]bithiophenyl-5-yl-pyridine (3) with ClRe(CO)₅ resulted in the isolation of complexes 4-6, ClRe(L)₂(CO)₃, where L=1, 2, or 3 respectively. The solid-state structure of 4 was determined by X-ray crystallography, which clearly shows the fac arrangement of the three CO ligands and the two 4-py-EDOT ligands arranged cis to one another. The metal complexes 4-6 have been characterized by ¹H and ¹³C NMR, ESI or FAB MS, FTIR, UV-Vis, fluorescence, and elemental analysis.     

Dithizone derivatives as sensitive water soluble chromogenic reagents for the ion chromatographic determination of inorganic and organo-mercury in aqueous matrices

Water-soluble sulfonate and the novel carboxylate analogues of dithizone, combined with ion interaction chromatography on a Dionex Acclaim 120 C18 silica column (250 x 4.6 mm id) with an eluent consisting of 10 mM tetrabutylammonium bromide and 60:40 methanol:water, have been developed as highly sensitive chromogenic ligands for the quantitative isocratic determination of inorganic and organo-mercury compounds in aqueous matrices in under 12 min. Using an optimised post column reagent system containing 0.65 mM dye, 0.5% Triton X-100 and 50 mM sodium hydroxide, good linearity (0-7.5 mg L(-1) R2 > 0.999), reproducibility using peak area measurements (RSD 0.69-1.38%, n = 8), and limits of detection (4-12 microg L(-1)) were achieved for methyl mercury, inorganic mercury and phenyl mercury.     

The preparation of fluxional tetrahydrides, (R  H or Me) and their reactions with CO,ButNC or HBr

The cyclometallated monohydrides

(R  H or Me) react with NaOPrⁱ/PrⁱOH/H₂ to give fluxional tetrahydrides, probably

. These are highly fluxional having magnetically equivalent hydridic hydrogens, even at ---100°C. When treated with HBr,

, gives

and with CO it gives a mixture of complexes which are probably

(2 isomers) and

. When treated with Bu^tNC this tetrahydride undergoes similar reactions but another (major) product is formed which appears to be binuclear and fluxional and is probably of type

, with four bridging hydrogens.     

Fused-s-triazino heterocycles. XI. Displacement reactions of 7,9-dichloro-2,5-bis(trichloromethyl)-1,3,4,6,9b-pentaazaphenalene

The preparation of 7,9-dichloro-2,5-bis(trichloromethyl)-1,3,4,6,9b-pentaazaphenalene ( 1e ) by the chlorination of 2-trichloromethyl-5-methyl-1,3,4,6,9b-pentaazaphenalene ( 1a ) using molecular chlorine is described. Displacement of one or both trichloromethyl groups of 1e by a variety of nucleophiles led to the corresponding 7,9-dichloro-2,5-bis-substituted or 7,9-dichloro mixed 2,5-disubstituted derivatives. The reaction of 1a with N-chlorosuccinimide proved not to be a useful route to 1e but instead led primarily to substitution of positions 7 and/or 9 by chlorine.     

Stereoselective C-glycosylation reactions of ribose derivatives: electronic effects of five-membered ring oxocarbenium ions

The factors controlling the highly alpha-selective C-glycosylation of ribose derivatives were determined by examining the stereoselective reactions of 18 ribose analogues differing in substitution at C-2, C-3, and C-4. The lowest energy conformers of the intermediate oxocarbenium ions display the C-3 alkoxy group in a pseudoaxial orientation to maximize electrostatic effects. To a lesser extent, the C-2 substituent prefers a pseudoequatorial position, and the alkyl group at C-4 has little influence on conformational preferences. In all cases, the product was formed by stereoelectronically preferred inside attack on the lowest energy conformer.     

Preparation and characterization of rhenium(I) compounds with amino ester derivatized diimine ligands. Investigations of luminescence. Crystal structures of Re(CO)3Cl(pyca-β-Ala-OEt) and Re(CO)3Cl(pyca-l-Asp(OMe)-OMe)

The title compounds were prepared in good yield by heating ester protected amino acids (H-l-Ala-OEt, H-β-Ala-OEt, H-L-Val-OMe, H-GABA-OMe, H-L-Asp(OMe)-OMe, H-L-Met-OMe) with Re(CO)₅Cl in the presence of pyridine-2-carboxaldehyde. The resulting novel complexes contain a bound, conjugated diimine ligand with a pendant ester group. All compounds were characterized by ¹H and ¹³C NMR, IR and UV-Vis spectroscopy. Compounds prepared from chiral amino esters give diastereomers because of the presence of a stereogenic metal center. Syntheses using Re(CO)₅Br as starting material were discontinued because of metathesis involving the chloride in the amino ester · HCl salts and the metal bromide. Photophysical studies on Re(CO)₃Cl(pyca-β-Ala-OEt), 2, show that it is luminescent in organic solvents in air at room temperature. The crystal structures of 2 and Re(CO)₃Cl(pyca-l-Asp(OMe)-OMe), 5, were determined.     

The effect of benzonitrile on the hydrogenation of phenylacetylene and 1-phenyl-1-propyne over a palladium/carbon catalyst

Benzonitrile reduces the rate of alkyne hydrogenation. However, it enhances the rate of styrene hydrogenation while reducing the rate of -methylstyrene hydrogenation.     

Use of phosphorus ligand NMR probes to investigate electronic and second-sphere solvent effects in ligand substitution reactions at manganese(II) and manganese(III)

Manganese/ligand association dynamics were studied using a series of structurally related anionic phosphorus ester ligand probes [CH(3)OP(O)(X)(Y)(-), where X = CH(3)O, CH(3)CH(2), or H and Y = O, S, or BH(3)]. Reactions of the probe ions with Mn(H(2)O)(6)(2+) and a manganese(III) porphyrin (Mn(III)TMPyP(5+)) were studied in aqueous solution by paramagnetic (31)P NMR line-broadening techniques. A satisfactory linear free energy relationship for reactions of the probe ions with Mn(H(2)O)(6)(2+) and Mn(III)TMPyP(5+) required consideration of both the basicity and solvent affinity of the probe ligands: log(k(app)) = log(k(0)) + alpha pK(a) + beta log(K(ext)), where k(0), alpha, and beta are metal complex dependent parameters and pK(a) and K(ext) represent the measured Bronsted acidity and water/n-butanol extraction constant for the probe anions, respectively. Reactions of Mn(H(2)O)(6)(2+) were relatively insensitive to changes in ligand basicity (alpha = -0.04) and favored the more hydrophilic anions (beta = -0.54). These observations are consistent with a dissociative ligand exchange mechanism wherein the outer-sphere complex is stabilized by hydrogen bonding between Mn(H(2)O)(6)(2+) and the incoming ligand. In contrast, reactions with Mn(III)TMPyP(5+) are accelerated by decreases in both the basicity (alpha = -0.43) and the hydrophilicity (beta = +0.97) of the probe. We conclude that reactions of Mn(III)TMPyP(5+) are also dissociative but that the aromatic groups of the porphyrin provide a hydrophobic environment surrounding the ligand binding site in Mn(III)TMPyP(5+). Thus, the probe/water solvent interactions must be significantly weakened in order to form the outer-sphere complex that leads to ligand substitution. This work demonstrates the utility of phosphorus relaxation enhancement (PhoRE) techniques for characterizing the second coordination sphere environment of metal complexes leading to ligation and will allow comparison of the second coordination spheres of Mn(H(2)O)(6)(2+) and Mn(III)TMPyP(5+) to those of other metal complexes.     

QCD analysis of non-singlet neutrino structure functions

We present a systematic analysis of all available neutrinoxF ₃ data, using an analytic parametrisation which incorporates second order QCD predictions forQ ² evolution. We find $$\Lambda _{\overline {MS} } = 0.30 \pm 0.13{\rm{ }}GeV$$ where the error is statistical, and both Fermi andW-boson propagator corrections have been made to the data. Neglect of the former has negligible effects, but neglect of the latter would increase Λ by ～0.1 GeV. We find that higher-twist effects are small and negative, and estimate their effect on the determination of Λ. We are unable to fit the data with higher-twist terms alone.