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Co I ‐ and Co 0 ‐Bipyridine Complexes Obtained by Reduction of CoBr 2 bpy: Electrochemical Behaviour and Investigation of Their Reactions with Aromatic Halides and Vinylic Acetates
Author(s) -
Polleux Laurent,
Labbé Eric,
Buriez Olivier,
Périchon Jacques
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400971
Subject(s) - chemistry , electrochemistry , halide , catalysis , cobalt , acetonitrile , cyclic voltammetry , electrolysis , inorganic chemistry , medicinal chemistry , photochemistry , organic chemistry , electrode , electrolyte
Abstract The electrochemical behaviour of CoBr 2 bpy (bpy=2,2′‐bipyridine) catalyst precursor in acetonitrile has been studied, revealing its possible reduction into the corresponding Co I and Co 0 complexes. These low‐valent cobalt species appear to be stable on the time scale of cyclic voltammetry. In the presence of aromatic halides, both complexes undergo oxidative addition, the latter Co 0 species allowing the activation of poorly reactive aromatic chlorides. The arylcobalt III and arylcobalt II obtained are reduced at the same potential as the original Co II and Co I complexes, respectively, resulting in the observation of overall ECE mechanisms in both cases. The electrochemical study shows that vinylic acetates competitively react with electrogenerated Co 0 species, leading to a labile complex. Preparative scale electrolyses carried out from solutions containing aromatic halides (ArX), vinyl acetate (vinylOAc) and a catalytic amount of CoBr 2 bpy lead to a mixture of biaryl (Ar‐Ar) and arene (ArH) as long as the potential is set on the plateau of the Co II ⇄ Co I reduction wave. The coupling product (Ar‐vinyl) is formed only if the electrolysis is performed on the plateau of the Co I /Co 0 reduction wave. A mechanism is proposed for the overall cobalt‐catalyzed coupling reaction between aromatic halides and allylic acetates.