CuII-salan compounds: Synthesis, characterization and evaluation of their potential as oxidation catalysts

We report the synthesis and characterization of several salan-type Cu-II complexes. Suitable crystals suitable for X-ray diffraction were obtained for several of the CuII complexes, including a "half-salen" compound, revealing square-planar coordination environments common to d(9) species. The Cu-II-salan complexes are tested as catalysts in sulfoxidation, alkene oxidation, and oxidative naphthol coupling. At room temperature the compounds exhibit low to moderate catalytic activity in sulfoxidations and alkene oxidations, but no activity in oxidative naphthol coupling. The saturated coordination environments around the Cu centers probably are the main reason for the lower catalytic activities compared to the Ti- and V-salan analogs. Spectroscopic and mass spectrometry studies revealed that the Cu-II-salan complexes decompose, in the presence of H2O2, significantly faster at 40 degrees C than at room temperature. The catalytic activity observed is probably due to the Cu-II-salan degradation products, observed in the mass spectrometry studies, and not to the original Cu-II-salan precursors. (C) 2013 Elsevier B.V. All rights reserved.