Abstract.DMAP stabilized palladium nanoparticles with a mean diameter of 3.4 0.5 nm are prepared from the aqueous phase reduction of Na 2 PdCl 4 using NaBH 4 in the presence of DMAP. TEM and UV-Vis spectroscopy characterization of the nanoparticle dispersion shows no obvious change in the nanoparticles several months after preparation.1 H NMR spectroscopy of the nanoparticles shows that the nanoparticle dispersion also contains a boron/DMAP complex and two palladium/DMAP complexes. One of the palladium complexes crystallizes out of the dispersion and is identified as Pd(DMAP) 4 (OH) 2 by X-Ray Crystallography. Following extensive analysis it is believed that the palladium/DMAP complexes are formed following the oxidation of the palladium nanoparticles. The prepared nanoparticle dispersion promotes selective hydrogen/deuterium (H/D) exchange on the carbon atoms to the endocyclic nitrogen atom on the DMAP stabilizing ligands through reaction with D 2 O. This activity is attributed to the presence of the nanoparticles rather than to the presence of the oxidized palladium/DMAP complexes.

An aqueous phase dispersion of Pd nanoparticles stabilised by 4-Dimethylaminopyridine (DMAP) promotes model Suzuki coupling reactions. The dispersion contains Pd nanoparticles of 3.4 0.5 nm and a Pd(II) species (Pd(DMAP) 4 (OH) 2 ) which forms following aerobic oxidation of the nanoparticles.The activity of the nanoparticle dispersion in promoting the Suzuki reactions is directly proportional to the size of the halogen on the substrate (as is usual for these coupling reactions) and also to the age of the nanoparticle dispersion.The Pd(DMAP) 4 (OH) 2 complex can be isolated from the dispersion and is found to be very active in promoting the reactions. Its formation following aerobic oxidation of the nanoparticles is proposed as the reason for the improved activity of the dispersion with age.The nanoparticles present in the dispersion can, through displacement of the stabilising ligand, be immobilised onto functionalised Multi Wall Carbon Nanotubes (MWCNT) and the composite formed is an active and recyclable catalyst. This MWCNT/Pd-DMAP NP composite acts as a reservoir of dissolved Pd species, which function as homogeneous catalysts under reaction conditions.

Publication informationCatalysis Today, 139 (3): 154-160Publisher Elsevier Item record/more information http://hdl.handle.net/10197/4001 Publisher's statementThis is the author's version of a work that was accepted for publication in Catalysis Today. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Catalysis Today, 139 (3) We have studied the effect of several different variables on the rate of the selective H-D exchange activity for a model pyridine, i.e. 4-Dimethylaminopyridine (DMAP).These variables include temperature, nanoparticle aging, nanoparticle re-reduction with H 2 and nanoparticle immobilisation onto multi-walled carbon nanotubes (MWCNT). We have also extended the study to related pyridine containing molecules.