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Electroreductive Palladium‐Catalysed Ullmann Reactions in Ionic Liquids: Scope and Mechanism
Author(s) -
Pachón Laura Durán,
Elsevier Cornelis J.,
Rothenberg Gadi
Publication year - 2006
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.200606132
Subject(s) - chemistry , catalysis , reagent , ionic liquid , electrochemistry , palladium , solvent , catalytic cycle , ionic bonding , inorganic chemistry , combinatorial chemistry , electrode , organic chemistry , ion
A room‐temperature catalytic alternative to the Ullmann reaction is presented, based on electroreductive homocoupling of haloarenes catalysed by palladium nanoparticles. The particles are generated in situ in an electrochemical cell, and electrons are used to close the catalytic cycle and provide the motivating force for the reaction. This system gives good yields using iodo‐ and bromoarenes, and requires only electric current and water as reagents. Using an ionic liquid solvent combines the advantages of excellent conductivity and cluster stabilising. The solvent is reusable at least five times. Kinetic experiments at different electrode potentials show that the two‐electron oxidation of water closes the catalytic cycle by regenerating the Pd(0). A mechanism involving radical anion formation is proposed. The advantages and limitations of this new system for carbon‐carbon homocoupling and cross‐coupling are discussed.