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Palladium Supported on Cross‐Linked Imidazolium Network on Silica as Highly Sustainable Catalysts for the Suzuki Reaction under Flow Conditions
Author(s) -
Pavia Cinzia,
Ballerini Eleonora,
Bivona Lucia Anna,
Giacalone Francesco,
Aprile Carmela,
Vaccaro Luigi,
Gruttadauria Michelangelo
Publication year - 2013
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201300215
Subject(s) - palladium , catalysis , chemistry , phenylboronic acid , x ray photoelectron spectroscopy , magic angle spinning , metal , nuclear chemistry , inorganic chemistry , chemical engineering , organic chemistry , nuclear magnetic resonance spectroscopy , engineering
Highly cross‐linked imidazolium‐based materials, obtained by radical oligomerization of bis‐vinylimidazolium salts in the presence of 3‐mercaptopropyl‐modified silica gel, were used as supports for palladium catalysts. Thanks to the high imidazolium loading these materials were able to support a high amount of the metal (10 wt%). Such materials were characterized by several techniques ( 13 C magic angle spinning nuclear magnetic resonance, the Brunauer–Emmett–Teller technique, X‐ray photoelectron spectroscopy, and transmission electron microscopy). The palladium catalysts displayed good activity allowing the synthesis of several biphenyl compounds in high yields working with only 0.1 mol% of palladium loading at 50 °C in ethanol/water under batch condition. Moreover, a flow apparatus, to optimize the efficiency of the isolation of the pure products and minimize waste (E‐factor), was investigated. For the first time the palladium catalyst and base (K 2 CO 3 ) were placed in two separate columns allowing an easy recovery of the products with very low E‐factor values (<4). Waste production was reduced by over 99% compared to classic batch conditions. Because of the high Pd loading only 42 mg of catalysts were employed in the Suzuki reaction between 160 mmol of 4‐bromotoluene and 180 mmol of phenylboronic acid. No loss in activity was observed.