Catalytic specificity of linear polystyrene-stabilized Pd nanoparticles during Ullmann coupling reaction in water and the associated mechanism

Publication date: Available online 22 November 2017 Source:Journal of Organometallic Chemistry Author(s): Atsushi Ohtaka, Akira Sakon, Asuka Yasui, Taira Kawaguchi, Go Hamasaka, Yasuhiro Uozumi, Tsutomu Shinagawa, Osamu Shimomura, Ryôki Nomura In the present work, heterogeneous Pd nanoparticle catalysts supported on linear polystyrene (PS-PdNPs) were used to promote Ullmann coupling reactions in water. The coupling reaction of 4-bromotoluene proceeded readily in the presence of methanol as the external reductant to give 4,4'-dimethylbiphenyl in 85% yield. In contrast, only a trace of the coupling product was obtained when using ethanol or 2-propanol. Higher yields were also observed for aryl bromides than for aryl iodides. The difference in the yields obtained from 4-iodotoluene and 4-bromotoluene is attributed to variations in the rate of reduction to reform Pd(0) species. The leaching of Pd species into the reaction medium has a negative effect on the Ullmann coupling reaction. The unique reactivity of PS-PdNPs and mechanistic pathway are discussed herein.
Source: Journal of Organometallic Chemistry - Category: Chemistry Source Type: research

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