Cationic iridium(1) complexes of chiral phosphanodihydrooxazoles were uscd as catalysts for the enantioselective hydrogenation of prochiral N-alkyl and N-aryl imines. The complexes are air-stable crystalline solids that can be readily prepared and are easy to handle. The structures of two complexes were determined by X-ray analysis. For N-alkyl imines of acetophenone, enantiomeric excesses of up to 79% were obtained. Dialkyl ketimines and cyclic imines showed lower reactivity and selectivity. A remarkable dilution effect was observed for the hydrogenation of the N-phenyl imine of acetophenone: decreasing the substrate and catalyst concentration led to a signifi- Keywords

This paper reports wurtzite-type CdS nanostructures synthesized via a hydrothermal reaction route using dithiol glycol as the sulfur source. The reaction time was found to play an important role in the shape of the CdS nanocrystals: from dots to wires via an oriented attachment mechanism. This work has enabled us to generate nanostructures with controllable geometric shapes and structures and thus optical properties. The CdS nanostructures show a hexagonal wurtzite phase confirmed by X-ray diffraction and show no evidence for a mixed phase of cubic symmetry. The Raman peak position of the characteristic first-order longitudinal optical phonon mode does not change greatly, and the corresponding full width at half-maximum is found to decrease with the CdS shape, changing from nanoparticles to nanowires because of crystalline quality improvement. The photoluminescence measurements indicate tunable optical properties just through a change in the shape of the CdS nanocrystals; i.e., CdS nanoparticles show a band-edge emission at approximately 426 nm in wavelength, while the CdS nanowires show a band-edge emission at approximately 426 nm as well as a weaker trap-state green emission at approximately 530 nm in wavelength. These samples provide an opportunity for the study of the evolution of crystal growth and optical properties, with the shape of the nanocrystals varying from nearly spherical particles to wires.