Star-shaped block copolymer stabilized palladium nanoparticles for efficient catalytic Heck cross-coupling reactions

Abstract

Palladium nanoparticles of improved stability against aggregation were prepared using 5-arm star-shaped block copolymers with a poly(ethylene oxide) (PEO) core and a poly(e-caprolactone) (PCL) corona as templates. The PEO core of these star-shaped block copolymers could be swollen with palladium acetate (Pd(OAc) 2 ) in N,N-dimethylformamide (DMF), and Pd nanoparticles were obtained by reduction with NaBH 4 . This procedure resulted in well defined Pd nanoparticles that were stabilized against aggregation due to a barrier of PCL chains. Transmission electron microscopy (TEM) experiments strongly suggested that one Pd nanoparticle was formed inside each star-shaped block copolymer. The stability of the Pd nanoparticles with respect to aggregation was strongly dependent on the length of the PCL chains. Subsequently, these nanoparticles were evaluated for their capability to act as catalysts in Heck coupling reactions. These reactions were performed in an automated synthesizer and monitored by GC-MS revealing that these particles are highly active for the catalytic reactions mentioned. Up to 99% conversion was observed for the coupling of styrene with 4-bromoacetophenone within 24 h at a catalyst loading of 0.1 mol%. Experimental Chemicals and reagentsAll reagents were used without further purification unless stated otherwise. Solvents were purchased from Biosolve Ltd.

Transition‐metal nanoparticles: synthesis, stability and the leaching issue

“…[73] The PEO core was swelled with Pd(OAc) 2 in N,N-dimethyl-formamide (DMF), and Pd NPs were obtained by reduction with NaBH 4 . Transmission electron microscopy studies strongly suggested that one Pd NP was formed inside each star-shaped block copolymer.…”

N,N‐Dimethylformamide as a Reaction Medium for Metal Nanoparticle Synthesis

“…[4] This uniquely versatile and powerful chemical has been used as a solvent in a wide variety of synthetic procedures, including: preparation of colloids, [5][6][7] synthesis of block-copolymers, [8,9] and many types of organic chemistry reactions. [10] The important role played by DMF as a solvent and reaction medium has motivated studies related to its redox activity.…”

Acyclic Triene Metathesis Polymerization with Chain‐Stoppers: Molecular Weight Control in the Synthesis of Branched Polymers

“…In addition, hyperbranched polymers can be used for the preparation of polymeric core-shell architectures [14,15] opening application possibilities as drug-delivery systems [16,17] due to their encapsulation behaviors [18,19] in a similar fashion as dendrimers [20,21] or star-shaped block copolymers. [22,23] Moreover, such coreshell macromolecules were shown to stabilize metalnanoparticles, [24,25] act as catalysts, [26,27] or enable sensoric applications. [28,29] Due to these interesting and manifold application possibilities of branched macromolecules and the lack of knowledge regarding the preparation of hyperbranched polymers via ADMET type metathesis chemistry, we investigated the ATMET of triglyceride 1 with different amounts of methyl acrylate (MA) as a chain stopper in order to prevent full cross-linking of 1 and to obtain branched polymers of different molecular weights in a straightforward one step one pot approach.…”