The electronic effect of 4,4′-disubstituted 2,2′-bipyridine ligands on the copper-catalysed oxidative coupling of 2,6-dimethylphenol

✍ Scribed by Peter G. Aubel; Shaista S. Khokhar; Willem L. Driessen; Ger Challa; Jan Reedijk

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 85 KB
• Volume: 175
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/s1381-1169(01)00212-6

✦ Synopsis

The ligands bipyridine (bpy), 4,4 -dimethoxy-2,2 -bipyridyl (dMeObpy), 4,4 -dimethyl-2,2 -bipyridyl (dMebpy), 4,4dichloro-2,2 -bipyridyl (dClbpy) and 4,4 -dinitro-2,2 -bipyridyl (dNO 2 bpy), when combined with copper(II) nitrate render active catalysts. The highest activity was found for bpy as the ligand. The ligands dMeObpy and dMebpy, with their electron-donating substituents, render the copper ions less electrophilic than unsubstituted bpy and so decrease the oxidation rate of 2,6-dimethylphenol (DMP). One would have expected an increase in the oxidation rate of DMP with the ligands dClbpy and dNO 2 bpy, having electron-withdrawing substituents, which render the copper ions more electrophilic. However, probably due to a stabilisation of the copper(I) species, which retards the reoxidation to Cu(II), the overall reaction rate decreases with dClbpy and dNO 2 bpy.