Madeleine H. Moore

Facile intermolecular aromatic C–F bond activation reaction of [Ru(dmpe)2H2](dmpe = Me2PCH2CH2PMe2)

cis-[Ru(dmpe)2H2] reacts at –78 °C with hexafluorobenzene to generate the pentafluorophenyl hydride complex,trans-[Ru(dmpe)2(C6F5)H]; reaction also takes place with C6F5H, C6F5CF3, C6F5OCH3,1,2,3,4-C6F4H2 and 1,2,3-C6F3H3 to yield products from C–F insertion exclusively.

Molecular and crystal structure of d(CGCGmo4CG) : N4-methoxycytosine•guanine base-pairs in Z-DNA

The base analogue N4-methoxycytosine (mo4C) is ambivalent in its hydrogen-bonding potential, since it forms stable base-pairs with both adenine and guanine in oligomer duplexes. To investigate the base-pair geometry, the structure of d(CGCGmo4CG) has been determined by single-crystal X-ray diffraction techniques. The d(CGCGmo4CG)2 crystallized in a left-handed double helical structure (Z-type). Refinement using 2559 reflections between 10 and 1.7 A converged with a final R = 0.181 (Rw = 0.130) including 68 solvent molecules. The orthorhombic crystals are in the space group P212121, with cell dimensions a= 18.17 A, b = 30.36 A, c = 43.93 A. The mo4C · G base-pair is of the wobble type, with mo4C in the imino form, and the methoxy group in the syn configuration.

Enhancing the yield and diastereoselectivity of the Pictet-Spengler reaction : a highly efficient route to cis-1,3-disubstituted tetrahydro-β-carbolines

Abstract Under conditions of kinetic control, the cis-diastereoselectivity of the Pictet-Spengler reaction between tryptophan esters and aldehydes can be controlled by varying the size of the ester group; the reaction proceeds in essentially quantitative yield with most aldehydes when conducted in chloroform in the presence of molecular sieves.

Intermolecular C–F and intramolecular C–H activation reaction of [Re(η5-C5Me5)(CO)3] with hexafluorobenzene: crystal and molecular structure of [Re(η6-C5Me4CH2)(CO)2(C6F5)]

Photochemical reaction of [Re(η5-C5Me5)(CO)3] with hexafluorobenzene yields [Re(η6-C5Me4CH2)(CO)2(C6F5)] formed by insertion into a C–F bond of C6F6 and concomitant insertion into a methyl C–H bond; the reactions of [Re(η6-C5Me4CH2)(CO)2(C6F5)] with PMe3 and with HCl show that the (η6-C5Me4CH2) ligand is subject to both nucleophilic and electrophilic attack.

From Molecular Ribbons to a Molecular Fabric

Ion-pair reinforced, hydrogen-bonded molecular ribbons are knitted together through ammonium carboxylate salt bridges into undulating sheets wherein each component participates in three ion-pairing interactions and up to twelve hydrogen bonds.

Studies in Werner clathrates. Part 5. Thermal analysis of bis(isothiocyanato)tetra(4-vinylpyridine)nickel(II) Inclusion compounds. Crystal structure of the Ni(NCS)2(4-vipy)4·2CHCl3 clathrate

Abstract The clathrate structure Ni(NCS) 2 (4-Vipy) 4 ·2CHCl 3 has been elucidated. The Ni(NCS) 2 (4-Vipy) 4 host molecule has an octahedral coordination and ‘propeller’ conformation. The CHCl 3 guest molecules occupy different cavities whose shapes and sizes are portrayed by volume calculations. Differential Thermal Analyses (DTA) and Gravimetric Thermal Analyses (GTA) were carried out on a series of clathrates comprising this host and a variety of guest molecules. An enthalpy change value for the ‘guest release reaction’ in each clathrate was obtained from the DTA experiments. The solubility of this host in these same guest solvents was measured in order to obtain a better understanding of the clathration process.

Product diversity in cyclisations of maleamic acids: the imide–isoimide dichotomy

Cyclisation of maleamic acids with acetic anhydride in dimethylacetamide (DMA) at ca. 75 °C, with or without added cobalt naphthenate, gives predominantly maleimides when the parent maleic anhydride is unsubstituted. However, when the maleic anhydride has either one or two methyl substituents, the products are 95% maleisoimides (5-imino-2,5-dihydrofuran-2-ones). In contrast all maleamic acids investigated, regardless of the extent of substitution, give exclusively maleimides when heated in acetic acid under reflux. Isoimide formation in the Ac2O–DMA–cobalt naphthenate procedure appears to arise from kinetic control, since the isoimide preference was reduced at higher reaction temperature. The preferred Z-stereochemistry of the isoimide 3 is confirmed by X-ray crystallography.

DNA–Drug Refinement: a Comparison of the Programs NUCLSQ, PROLSQ, SHELXL93 and X‐PLOR, Using the Low‐Temperature d(TGATCA)–Nogalamycin Structure

In an earlier study [Smith, Davies, Dodson & Moore (1995). Biochemistry, 34, 415-425] the crystal structure of the d(TGATCA)-nogalamycin complex was determined to 1.8 A and refined with PROLSQ to R = 19.5% against 4767 reflections with F> 1sigma(F). A low-temperature crystallographic study on this complex has now been performed. Native data collection at liquid-nitrogen temperature (120 K) improved the resolution to 1.4 A. The structure has now been refined against these new diffraction data in the resolution range 8-1.4 A using NUCLSQ, PROLSQ, SHELXL93 and X-PLOR, in order to determine to what extent the resulting DNA conformation and associated solvent structure would differ and to examine the suitability of these programs for the refinement of oligonucleotide structures. With the advent of more DNA-protein structure determinations, it is of interest to see how well the protein-refinement packages, PROLSQ and X-PLOR, and the small-molecule program, SHELXL93, are able to accommodate DNA. Comparisons are made between the dictionaries, weights and restraints used and the final models obtained from each program. Although the final R values, using all data in the resolution range 8.0-1.4 A, from PROLSQ (22.8%), SHELXL93 (R1 =21.7% after isotropic refinement) and X-PLOR (24.4%) are higher than the R value from the NUCLSQ refinement (21.2%), the root-mean-square deviations between the four final models are very small. Using this high-quality 8.0-1.4 A data set neither the dictionary nor the refinement program leave an imprint on the final fully refined complex. Likewise, the helical parameters and backbone conformation including sugar-puckering modes are not influenced by the refinement procedure used. Although a different number of water molecules is found in each refinement, varying from 62 (X-PLOR) to 86 (NUCLSQ), the first hydration sphere is well conserved in all four models.

Synthesis, molecular structure and NMR spectroscopy of atransition-metal bifluoride complex: formation via C–Factivation or reaction with Et3N·3HF

The bifluoride complex, trans-[Ru(dmpe) 2 (H)(HF 2 )] (dmpe = Me 2 PCH 2 CH 2 PMe 2 ), is generated by reaction of cis-[Ru(dmpe) 2 H 2 ] either with fluoroarenes (C 6 F 6 , C 6 F 5 H and others) or by reaction with Et 3 N·3HF; its solid-state structure, established crystallographically, reveals a Ru(η 1 -FHF) moiety with a long Ru–F bond and an F···F distance close to that in bifluoride salts, while the presence of the same complex in solution is shown by low-temperature NMR spectra.

Dialkyldicarbonyl rhenium complexes (η5-C5Me5)Re(CO)2R2, R = Me and Et. X-ray structure of trans-(η5-C5Me5)Re(CO)2Et2

The compounds cis-(η5-C5Me5)Re(CO)2Me2 and trans-(η5-C5-Me5)Re(CO)2Et2 were prepared by alkylation of cis-(η5-C5Me5)Re(CO)2Cl2 using the corresponding organocopper (RCu). Photolysis of cis-(η5-C5Me5)Re(CO)2Me2 in frozen toluene-d8 readily produces the trans-(η5-C5Me5)Re(CO)2Me2. All the compounds were characterized by spectroscopy and analyses, and the stereochemistry assigned from examination of v(CO) IR intensities; additionally trans-(η5-C5Me5)Re(CO)2Et2 was studied by X-ray crystallography. Crystal data: monoclinic P21/m, a = 8.034(8) A, b = 11.991(8) A, c = 8.69(2) A, β = 91.38°, V = 837(2) A3, Z = 4, λ(Mo K α) = 0.7107 A, RF = 0.0285 and wRI = 0.071 for 1670 measured reflections with 5 < 2ϑ < 50°.