The Effect of PEGylated Dendrimers on the Catalytic Activity and Stability of Palladium Particles in the Suzuki Reaction
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The Effect of PEGylated Dendrimers on the Catalytic Activity and Stability of Palladium Particles in the Suzuki Reaction Christian Ga¨bler • Janine Jeschke • Gulnar Nurgazina • Sascha Dietrich • Dieter Schaarschmidt • Colin Georgi • Maik Schlesinger • Michael Mehring • Heinrich Lang
Received: 25 October 2012 / Accepted: 24 January 2013 / Published online: 20 February 2013 Ó Springer Science+Business Media New York 2013
Abstract Stable dendrimer-coated Pd particles were synthesized using the wet-chemical borohydride reduction method of Pd(II) salts in the presence of low-generation (poly)ethylene glycol-terminated amidoamine-based dendrimers. The identity and structure of the Pd-containing colloids were analyzed by FT-IR spectroscopy, X-ray powder diffraction, thermogravimetric analysis, atom absorption spectroscopy and UV–Vis spectroscopy. Dynamic light scattering experiments have been performed to determine the hydrodynamic diameter of the particles (350–900 nm). The performance of the thus obtained dendrimer-stabilized Pd particles in Suzuki C,C cross-coupling reactions of aryl halides and phenyl boronic acid was examined. Turn over numbers of up to 930 could be achieved. The influence of the dendritic stabilizers on the particle size along with the catalytic performance is presented. Keywords Particles Palladium (Amidoamine) dendrimers (Poly)ethylene glycol
C. Ga¨bler J. Jeschke S. Dietrich D. Schaarschmidt C. Georgi H. Lang (&) Department of Inorganic Chemistry, Faculty of Natural Sciences, Institute of Chemistry, Chemnitz University of Technology, Straße der Nationen 62, 09111 Chemnitz, Germany e-mail: [email protected] G. Nurgazina Department of Chemistry, Faculty of Natural Sciences, L.N.Gumilyov Eurasian National University, Munaitpasov Street 5, 010008 Astana, Kazakhstan M. Schlesinger M. Mehring Department of Coordination Chemistry, Faculty of Natural Sciences, Institute of Chemistry, Chemnitz University of Technology, Straße der Nationen 62, 09111 Chemnitz, Germany
1 Introduction Nanosized metallic particles exhibiting a large surfaceto-volume ratio gained considerable interest in the application as effective catalysts for a variety of chemical transformations [1–4]. Presently, scientific efforts are directed to nanocatalysis, in the field of heterogeneous catalysis, in which the nanoparticles (NPs) are supported on a solid surface (e.g. silica [5, 6], alumina [7, 8]) and in homogeneous catalysis applying colloidal NPs as catalytic active species, respectively [9, 10]. Because metal NPs are thermodynamically unstable with respect to agglomeration and precipitation phenomena, the colloids tend to lose their catalytic reactivity and selectivity [11]. Aggregation of NPs can be avoided by surrounding the appropriate nanoparticle with an electrical double layer of adsorbed ions (e.g. citrate and chloride) or by adsorption of weakly bounded organic surfactant molecules (e.g. long-chain alkyl compounds, tensides, polymers, dendrimers ) in the preparation progress, thus prov
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