Palladium-catalyzed amination of aryl nonaflates

The first detailed study of the palladium-catalyzed amination of aryl nonaflates is reported. Use of ligands 2-4 and 6 allows for the catalytic amination of electron-rich and -neutral aryl nonaflates with both primary and secondary amines. With use of Xantphos 5, the catalytic amination of a variety of functionalized aryl nonaflates resulted in excellent yields of anilines; even 2-carboxymethyl aryl nonaflate is effectively coupled with a primary alkylamine. Moderate yields were obtained when coupling halo-aryl nonaflates with a variety of amines, where in most cases the aryl nonaflate reacted in preference to the aryl halide. Overall, aryl nonaflates are an effective alternative to triflates in palladium-catalyzed C-N bond-forming processes due to their increased stability under the reaction conditions.     

Stable Hydrogen-Bonded Spherical Capsules Formed from Self-Assembly of Pyrogallol[4]arenes

The self-assemblies of two pyrogallol[4]arenes held together by 48 intermolecular hydrogen bonds stably associate in the form of spherical hexameric capsules. The molecular structures of two hexameric capsules with large interior space were analyzed by single crystal X-ray crystallography.     

Hybrid fluorocarbon-hydrocarbon CO2-philic surfactants. 2. formation and properties of water-in-CO2 microemulsions

Hybrid fluorocarbon-hydrocarbon (F-H) sulfate surfactants are shown to be efficient stabilizers in water-in-CO2 (w/c) microemulsions. The chain structure and F-H ratio affect the regions of P-T phase stability and aggregation structure in these w/c phases. High-pressure near-infrared spectroscopy and small-angle neutron scattering measurements of microemulsified water provide evidence for the stabilization of w/c microemulsion droplets. The relative lengths of the two chains were found to influence the favored aggregation structure: for symmetric chain surfactants (F8H8, F7H7) spherical reverse micelles are present, but for asymmetric chain surfactants (F7H4, F8H4) extended cylinder aggregates form. These changes in aggregation are consistent with different surfactant packing parameters owing to the controlled variations in molecular structure. Furthermore, the general order of w/c phase transition pressures (F8H8 < F7H7 and F8H4 < F7H4) is in line with estimations of surfactant fractional free volume, as proposed by Johnston et al. (J. Phys. Chem. B 2004, 108, 1962-1966). Studies of adsorption at the poly(dimethylsiloxane)-water interface are shown to be valuable for assessing the CO2-philicity of new surfactants. All in all, the symmetric F8H8 and F7H7 analogues are seen to be the most efficient compounds from this class for applications in CO2.     

PHOTOCHEMISTRY OF TYPE I ACID-SOLUBLE CALF SKIN COLLAGEN: DEPENDENCE ON EXCITATION WAVELENGTH

Although previous studies have demonstrated that the predominant photochemistry of type I collagen under 254 nm irradiation may be attributed either to direct absorption by tyrosine/phenylalanine or to peptide bonds, direct collagen photochemistry via solar UV wavelengths is much more likely to involve several age- and tissue-related photolabile collagen fluorophores that absorb in the latter region. In this study, we compare and contrast results obtained from irradiation of a commercial preparation of acid-soluble calf skin type I collagen in solution with UVC (primarily 254 nm), UVA (335–400nm) and broad-band solar-simulating radiation (SSR; 290^1–00nm). Excitation spectroscopy and analysis of photochemically induced disappearance of fluorescence (fluorescence fading) indicates that this preparation has at least four photolabile fluorescent chromophores. In addition to tyrosine and L-3,4-dihydroxyphenylalanine, our sample contains two other fluorophores. Chromophore I, with emission maximum at 360 nm, appears to be derived from interacting aromatic moieties in close mutual proximity. Chromophore II, with broad emission at430–435 nm, may be composed of one or more age-related molecules. Collagen fluorescence fading kinetics are sensitive to excitation wavelength and to conformation. Under UVC, chromophore I fluorescence disappears with second-order kinetics, indicating a reaction between two proximal like molecules. Adherence to second-order kinetics is abrogated by prior denaturation of the collagen sample. A new broad, weak fluorescence band at400–420 nm, attributable to dityrosine, forms under UVC, but not under solar radiation. This band is photolabile to UVA and UVB wavelengths. Amino acid analysis indicates significant destruction of aromatic amino acids under UVC, but not under UVA or SSR. When properly understood, collagen fluorescence fading phenomena may act as a sensitive molecular probe of structure, conformation and reactivity.     

Synthesis of C2-symmetric trans-2,6-diarylpiperidinones via aryl cuprate addition: an unexpected stereochemical outcome

An efficient procedure for the preparation of trans-2,6-diaryl piperidinones has been developed. Addition of aryl Grignard reagents to 2-aryl dihydropyridones under catalytic copper promoted conditions generates the trans isomer exclusively, an unprecedented stereochemical event. The X-ray structures of both starting material and product have been solved and shed light on the steric constraints and substrate geometry leading to the observed product. The reaction conditions tolerate a variety of aromatic nucleophiles to generate C₂-symmetric products in good overall yields.     

Two new terpyridine dimanganese complexes: a manganese(III,III) complex with a single unsupported oxo bridge and a manganese(III,IV) complex with a dioxo bridge. Synthesis, structure, and redox properties

Two new terpyridine dimanganese oxo complexes [Mn(2)(III,IV)(mu-O)(2)(terpy)(2)(CF(3)CO(2))(2)](+) (3) and [Mn(2)(III,III)(mu-O)(terpy)(2)(CF(3)CO(2))(4)] (4) (terpy = 2,2':6,2' '-terpyridine) have been synthesized and their X-ray structures determined. In contrast to the corresponding mixed-valent aqua complex [Mn(2)(III,IV)(mu-O)(2)(terpy)(2)(H(2)O)(2)](3+) (1), the two Mn atoms in 3 are not crystallographically equivalent. The neutral binuclear monooxo manganese(III,III) complex 4 exhibits two crystallographic forms having cis and trans configurations. In the cis complex, the two CF(3)CO(2)(-) ligands on each manganese adopt a cis geometry to each other; one CF(3)CO(2)(-) is trans to the oxygen of the oxo bridge while the second is cis. In the trans complex, the two coordinated CF(3)CO(2)(-) have a trans geometry to each other and are cis to the oxo bridge. The electrochemical behavior of 3 in organic medium (CH(3)CN) shows that this complex could be oxidized into its corresponding stable manganese(IV,IV) species while its reduced form manganese(III,III) is very unstable and leads by a disproportionation process to Mn(II) and Mn(IV) complexes. Complex 4 is only stable in the solid state, and it disproportionates spontaneously in CH(3)CN solution into the mixed-valent complex 3 and the mononuclear complex [Mn(II)(terpy)(2)](2+) (2), thereby preventing the observation of its electrochemical behavior.     

Cluster Chemsitry. 96. Penta- and hexa-nuclear ruthenium cluster complexes derived from reactions of cyclopentadienes with Ru5(μ5-C2PPh2)(μ-PPh2)(CO)13

The reactions between Ru₅( ₅-C₂PPh₂)(gm-PPh₂(CO)₁₃ (1) and cyclopentadienes afforded the hexanuclear clusters Ru₆( ₆-C)( ₃-PPh₂)₂(CO)₁₀(-C₅ R ₅) [R ₅ = H₅ (2), H₄Me (3), Me₅ (4)] which contain an encapsulated carbide and a face-capping ₃-CH group, formed by cleavage of CC and CP bonds of the C₂PPh₂ moiety in1. In the reaction with cyclopentadiene, the unusual ligand C₁₃H₁₂O, formed by combination of C₂, CO and two molecules of C₅H₆ (or one molecule of dicyclopentadien), was characterized in the complex Ru₅( ₄-PPh) ( ₄-C₁₃H₁₂O)(-PPh₂(CO)₁₁(-C₅H₅) (5). In the reaction with pentamethylcyclopentadiene, the vinylidene complex Ru₅( ₃-CCHPh)( ₄-PPh)( ₄-PPh) (-PPh₂)(CO)₉(-C₅Me₅) (6) was also formed.     

Determination of trace impurities in tin by neutron activation analysis

A method was developed for the determination of 15 trace elements in tin. High-purity tin samples (99.9999% and 99.999%) as well as tin of technical quality were analysed. Reactor neutron activation of the tin samples was followed by distillation of the matrix activities from a HBr−H₂SO₄ medium and Ge(Li) gamma-ray spectrometry of the distillation residue. The sensitivity of the method is generally high. For the high-purity samples the detection limits vary from 0.02 ppb (scandium) to 200 ppb (iron) for irradiation of 1 g of tin for 1 week at a thermal flux of 5·10¹²n·cm⁻². ·sec⁻¹. To decontaminate the surface of the tin samples, pre- and post-irradiation etching procedures were applied. The efficiency of these etching techniques was studied.     

Automorphism groups of finite distributive lattices with a given sublattice of fixed points

For a latticeL, aL is a fixed point ofL if and only iff(a)=a for every automorphismf ofL. Let Aut (L) andS (L) denote the group of automorphisms ofL and the sublattice of fixed points ofL, respectively. It is shown that ifG is a finite group other thanZ ₂ ² ,Z ₂ ³ ,Z ₂ ⁴ ,Z ₃ ² or the quaternion group of order 8 andL is a finite automorphism free distributive lattice that is not near Boolean then there is a finite distributive latticeL such that Aut (L)G andS(L)L.The support of the National Research Council of Canada is gratefully acknowledged.