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

•Preparation and catalytic activity of several new CuII–salan complexes.•First structural characterization of a chiral half-salen based complex.•The catalytic activity observed is probably due to CuII–salan degradation products.

We report the synthesis and characterization of several salan-type CuII 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 d9 species. The CuII–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 CuII–salan complexes decompose, in the presence of H2O2, significantly faster at 40 °C than at room temperature. The catalytic activity observed is probably due to the CuII–salan degradation products, observed in the mass spectrometry studies, and not to the original CuII–salan precursors.

Graphical abstractThe catalytic oxidation activity of the several CuII–salan complexes reported is probably due to their degradation products, and not to the original CuII–salan catalyst precursors.Figure optionsDownload full-size imageDownload as PowerPoint slide