Self-organized ZnAl2O4 nanostructures grown on -sapphire

Self-organized ZnAl₂O₄ nanostructures with the appearance (in SEM) of high aspect ratio horizontal nanowires are grown on uncatalysed c-sapphire by vapour phase transport. The nanostructures grow as three equivalent crystallographic variants on c-sapphire. Raman and cathodoluminescence spectroscopy confirm that the nanostructures are not ZnO and TEM shows that they are the cubic spinel, zinc aluminate, ZnAl₂O₄, formed by the reaction of Zn and O with the sapphire substrate.     

Molecular Rydberg transitions. Intermediate coupling in simple bromides

An intermediate coupling analysis of the low-energy π → σ Rydberg transitions of hydrogen bromide, cyanogen bromide, acetylene bromide and alkyl bromides is presented. Exchange and spin-orbit coupling parameters are calculated and their variations discussed. The Br 5s orbital is delocalized in the larger alkyl bromides and Br 4p is heavily involved in π bonding in acetylene and cyanogen bromides.     

Copper activation of boronic acids: factors affecting reactivity

The generation of nucleophiles from the combination of aryl boronic acids and catalytic amounts of copper salt allows a reactivity distinct from other organometallic species, such as organolithiums or Grignard reagents. Here we examine how the electronic and steric properties of the boronic acid affect the formation of active nucleophiles and their subsequent reactivity with iminium‐type compounds, showing that electron‐rich substrates display reduced reactivity. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrical characterisation of phosphorus-doped ZnO thin films grown by pulsed laser deposition

Phosphorus-doped ZnO films were grown by pulsed laser deposition using a ZnO:P₂O₅-doped target as the phosphorus source with the aim of producing p-type ZnO material. ZnO:P layers (with phosphorus concentrations of between 0.01 to 1 wt%) were grown on a pure ZnO buffer layer. The electrical properties of the films were characterised from temperature dependent Hall-effect measurements. The samples typically showed weak n-type conduction in the dark, with a resistivity of 70 Ω cm, a Hall mobility of μ_n0.5 cm² V ⁻¹ s⁻¹ and a carrier concentration of n3×10¹⁷ cm⁻³ at room temperature. After exposure to an incandescent light source, the samples underwent a change in conduction from n- to p-type, with an increase in mobility and decrease in concentration for temperatures below 300 K.     

Nucleophilic Reactivity of a Copper(II)–Superoxide Complex

Metal‐bound superoxide intermediates are often implicated as electrophilic oxidants in dioxygen‐activating metalloenzymes. In the nonheme iron α‐ketoglutarate dependent oxygenases and pterin‐dependent hydroxylases, however, Fe^III–superoxide intermediates are postulated to react by nucleophilic attack on electrophilic carbon atoms. By reacting a Cu^II–superoxide complex ( 1 ) with acyl chloride substrates, we have found that a metal–superoxide complex can be a very reactive nucleophile. Furthermore, 1 was found to be an efficient nucleophilic deformylating reagent, capable of Baeyer–Villiger oxidation of a number of aldehyde substrates. The observed nucleophilic chemistry represents a new domain for metal–superoxide reactivity. Our observations provide support for the postulated role of metal–superoxide intermediates in nonheme iron α‐ketoglutarate dependent and pterin‐dependent enzymes.     

Application of the Suzuki reaction to the asymmetric desymmetrisation of 1,2- and 1,3-disubstituted bulky cobalt metallocenes

Reaction of (η⁵-cyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt with Hg(OAc)₂ (2.3 equiv) in 1:1 MeOH/CH₂Cl₂ followed by the addition of LiCl resulted in the formation of (η⁵-1,2-dichloromercuricyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt (33%) and its 1,3-isomer (6%). Following conversion into their corresponding diiodides these compounds were desymmetrised by Suzuki reactions with ArB(OH)₂ employing [(R)-BINAP]PdCl₂, with the highest ee of 24% being obtained for (η⁵-1-iodo-3-(2-methoxyphenyl)cyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt.     

Rapid, in situ synthesis of bidentate ligands: chromatography-free generation of catalyst libraries

The parallel synthesis of chiral bidentate ligands and their subsequent use in situ for a catalytic process is described. The ligands thus prepared gave comparable results to those obtained when the ligands were synthesized and purified by conventional means. This includes oxazolines and other compounds of similar complexity, meaning that for the first time these valuable compounds have been brought into the field of combinatorial catalysis.