Electron-rich salen-type Schiff base complexes of Cu(II) as catalysts for oxidation of cyclooctene and styrene with tert-butylhydroperoxide: A comparison with electron-deficient ones

Two square planar copper(II) complexes of tetradentate Schiff base ligands derived from aromatic aldehydes and 2,2'-dimethylpropandiamine (H-2{Salnptn(3-OMe)(2)}, H-2{hnaphnptn}) have been prepared and used as catalysts for oxidation of cyclooctene and styrene with tert-butylhydroperoxide (TBHP). Oxidation of cyclooctene with TBHP gave cyclooctene oxide as the sole product, but in the case of styrene a mixture of styrene oxide and benzaldehyde has been obtained in ca. 1:3 molar ratio. It has been shown that the rate and selectivity of reaction depend to the electron-donor ability Of substituents at the phenyl groups of the ligand and can be improved by introduction of n-electron-donating groups at the aromatic rings of salen-type Schiff bases. The structure of Cu{Salnptn(3-OMe)(2)} has been determined by X-ray crystallography at 291 K with results generally in agreement with those previously reported. The results suggest that the symmetrical Schiff base ligands are bivalent anions with tetradentate N2O2 donors derived from the phenolic oxygen and azomethine nitrogen atoms. (c) 2009 Elsevier B.V. All rights reserved.