Dioxomolybdenum(VI) complexes with linear and tripodal tetradenate ligands: Synthesis, structures and their use as olefin epoxidation catalysts

A series of linear and tripodal tetradentate ligands containing an amine-bis(phenolate) core were synthesized by Mannich condensations. Treatment of these ligands with MoO2(acac)2 (acac = acetylacetonate) in dichloromethane and methanol at room temperature gave the corresponding cis-dioxomolybdenum(VI) complexes in good yields. All these complexes were characterized by a wide range of spectroscopic methods (NMR, IR, and UV–Vis) and elemental analysis. The molecular structures of complexes MoO2(Ln) (n = 1–3, 5) were confirmed by single-crystal X-ray diffraction analysis. The catalytic activities of all complexes towards the epoxidation of styrene by tert-butyl hydroperoxide have also been investigated.

Graphical abstractSeveral dioxomolybdenum(VI) complexes with linear and tripodal tetradentate amine-bis(phenolate) ligands were synthesized in good yields. Their X-ray structures show cis-dioxo distorted octahedral geometry. The catalytic activities of these complexes towards the epoxidation of styrene by tert-butyl hydroperoxide have been investigated.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Several linear and tripodal tetradentate amine-bis(phenolate) ligands were synthesized. ► Dioxomolybdenum(VI) complexes with above ligands were prepared in good yields. ► All these complexes were characterized by NMR, IR, UV–Vis, and elemental analysis. ► X-ray structures of these complexes show cis-dioxo distorted octahedral geometry. ► All these complexes were evaluated as catalysts for the epoxidation of styrene.