Asymmetric allylic oxidation reactions catalyzed by a chiral nonracemic and C2-symmetric 2,2'-bipyridyl copper(I) complex

The evaluation of a chiral, nonracemic and C2-symmetric 2,2'-bipyridyl ligand in copper(I)-catalyzed asymmetric allylic oxidation reactions of a series of cyclic alkenes with tert-butyl peroxybenzoate is reported (up to 91% ee, the highest reported enantioselectivity for a bipyridyl ligand copper(I) complex to date).     

Group I cation templated formation of luminescent mono- and bis-substituted thionaphthol heterobimetallic complexes of Pr, Nd, Eu and Tb

Metathesis of lanthanide tris di-tert-butyl beta-diketonates ([Ln(thd)3] Ln=Pr, Nd, Eu, Tb) with one or two equivalents of group 1 salts of the sulfur bridged binaphtholate dianion [1,1'-S(2-OC10H4But(2)-3,6)2]2-, [M2L], M=K, Li affords luminescent mono- and bis-ligand substituted complexes ML[LnL(thd)2].L; M=K, Ln=Pr , Nd , Eu and Tb (L=thf, diethyl ether or toluene) and M(thf)2[LnL2(thd)]; M=Li, Ln=Pr , Nd , Eu , Tb . The potassium salt [K2L] affords mono-L substituted complexes most cleanly, while the lithium salt [Li2L] yields the bis-L substituted complexes most cleanly. The L ligands function as antenna for the sensitised lanthanide-centred emission in Eu3+ and Tb3+ complexes. The X-ray single-crystal structures of mono- and bis-L lanthanide complexes of Nd3+ are presented.     

Significant differences in the electrochemical behavior of the alpha-, beta-, gamma-, and delta-tocopherols (vitamin E)

Alpha-, beta-, gamma-, and delta-tocopherols can be oxidized in dry CH2Cl2 or CH3CN by one electron to form cation radicals that deprotonate to form the neutral phenoxyl radicals, which are then immediately further oxidized by one electron to the phenoxonium cations (an ECE electrochemical mechanism, where E signifies an electron transfer and C represents a chemical step, with the electrochemical mechanism having been determined by in situ spectroscopic analysis). The principal difference in the electrochemical behavior of the tocopherols relates to the stability of their associated phenoxonium cations. The phenoxonium cation of alpha-tocopherol is stable in solution for at least several hours, the phenoxonium cation of beta-tocopherol is stable for several minutes, and the phenoxonium cations of gamma- and delta-tocopherol are stable for <1 s. In dry CH2Cl2 containing >0.75 M acid (CF3COOH), the deprotonation reaction of the cation radicals can be completely inhibited resulting in the cyclic voltammetric behavior of the tocopherols appearing as chemically reversible one-electron oxidation processes (an E mechanism). In dry acid conditions, the cation radicals can be further oxidized by one electron to form the dications, which are unstable and immediately deprotonate. The high stability of the phenoxonium cation of alpha-tocopherol compared to the other tocopherols (and most other phenols) is a chemically important feature that may shed new light on understanding alpha-tocopherol's unique biological properties.     

Phosphine dissociation and diffusion on Si(001) observed at the atomic scale

A detailed atomic-resolution scanning tunneling microscopy (STM) and density functional theory study of the adsorption, dissociation, and surface diffusion of phosphine (PH(3)) on Si(001) is presented. Adsorbate coverages from approximately 0.01 monolayer to saturation are investigated, and adsorption is performed at room temperature and 120 K. It is shown that PH(3) dissociates upon adsorption to Si(001) at room temperature to produce both PH(2) + H and PH + 2H. These appear in atomic-resolution STM images as features asymmetric-about and centered-upon the dimer rows, respectively. The ratio of PH(2) to PH is a function of both dose rate and temperature, and the dissociation of PH(2) to PH occurs on a time scale of minutes at room temperature. Time-resolved in situ STM observations of these adsorbates show the surface diffusion of PH(2) adsorbates (mediated by its lone pair electrons) and the dissociation of PH(2) to PH. The surface diffusion of PH(2) results in the formation of hemihydride dimers on low-dosed Si(001) surfaces and the ordering of PH molecules along dimer rows at saturation coverages. The observations presented here have important implications for the fabrication of atomic-scale P dopant structures in Si, and the methodology is applicable to other emerging areas of nanotechnology, such as molecular electronics, where unambiguous molecular identification using STM is necessary.     

The coefficients of the Laurent series expansions of real analytic functions

Letf be a real analytic function of a real variable such that 0 is an isolated (possibly essential) singularity off. In the existing literature the coefficients of the Laurent series expansion off around 0 are obtained by applying Cauchy's integral formula to the analytic continuation off on the complex plane. Here by means of a conformal mapping we derive a formula which determines the Laurent coefficients off solely in terms of the values off and the derivatives off at a real point of analyticity off. Using a more complicated mapping, we similarly determine the coefficients of the Laurent expansion off around 0 where now 0 is a singularity off which is not necessarily isolated.     

Translational dynamics of a non-degenerate molecular shuttle imbedded in a zirconium metal–organic framework

A new [2]rotaxane molecular shuttle linker based on the binding of a 24-crown-8 ether macrocycle at a benzimidazole recognition site was synthesised. The shuttling dynamics of the linker were studied in solution and the structure confirmed by X-ray crystallography. A multivariate Zr(iv) MOF, UWDM-11, containing the new MIM linker and primary linker tetramethylterphenyldicarboxylate was synthesised and the translational motion of the molecular shuttle studied in the solid state. The use of a ¹³C enriched MIM linker allowed the dynamics of both activated and mesitylene-solvated UWDM-11 to be elucidated by VT ¹³C CPMAS SSNMR. The incorporation of mesitylene into the pores of UWDM-11 resulted in a significant increase in the barrier for thermally driven translation of the macrocycle.

An unsymmetrical molecular shuttle was incorporated into the octahedral cavities of a Zr(iv) MOF. ¹³C SSNMR showed that the presence of mesitylene in the pores results in an increase in the barriers for the thermally driven motion of the macrocycle.     

Electron spin resonance investigation of carbon-13 hyperfine interactions in nitrobenzene anion radical

Synthesis of carbon-13 enriched nitrobenzene which contains 22·5 mole per cent of nitrobenzene-1-¹³C and an equal amount of nitrobenzene-4-¹³C has been accomplished. We report the carbon-13 hyperfine interactions in the corresponding anion radicals in a variety of solvent media. In hexamethylphosphoramide a _C1 = -7·05 gauss and a _C4 = 6·14 gauss. These couplings change to -9·03 gauss and 5·31 gauss, respectively, when the solvent medium is dimethylformamide containing 0·598 mole fraction of water. The solvent dependence of a _C1 is consistent with the radical remaining planar as opposed to adopting a pyramidal conformation at the nitrogen when hydrogen bonds form between the radical anion and protic solvents. Data reported here provide an experimental means to estimate the spin density distribution in nitrobenzene anion.