RESUMEN
In this paper, a highly effective and scalable polyol-based modified procedure is reported, yielding shape-controlled Pd nanoparticles (NPs) formed via two distinct growth mechanisms as a function of apparent pH. Starting from tetraethylammonium tetrahydroxypalladate (TEA)2[Pd(OH)4], a halide-free precursor, the resulting shape of the NPs ranged from highly defective worm-like nanostructures to well-defined polyhedra (tetrahedra, octahedra and 5-fold twins) as shown by TEM, HRTEM, and STEM. The effect of the different synthesis parameters was thoroughly investigated, finding that apparent pH - modulated by adding diluted HNO3 - is the key parameter in determining the final size and shape of Pd NPs, whose evolution was followed during the reaction. A rational explanation of the observed shape modification as a function of apparent pH was proposed. The as-prepared Pd NPs, once dried, were analysed by means of XRD. DRIFT spectroscopy was used to show how CO binds on the Pd NPs after deposition on γ-Al2O3 as catalytic support.
RESUMEN
The cobalt(I)-catalyzed Diels-Alder reaction of propargylic phosphonium salts and longer chained alkyne-functionalized phosphonium salts with 1,3-dienes led to dihydroaromatic phosphonium salt intermediates which were directly used in a one-pot Wittig-type olefination reaction with aldehydes. Subsequent oxidation led to styrene- and stilbene-type products under formation of three new carbon-carbon bonds in a single synthetical step starting from three variable starting materials. The E/Z stereoselectivities of the products revealed that the dihydroaromatic phosphonium ylides behave as semistabilized ylides giving predominantly the E-configured products. The application of unsymmetrical 1,3-dienes as well as internal phosphonium functionalized alkynes is also described.
