In this work, (N-salicylidene) aniline and ((2-hydroxynaphtalen-1-yl)methylene) aniline derived MTO-Schiff base complexes, mono- and bis- MTO-salen complexes, bipyridine derived MTO-Lewis base and MoO2Cl2-Lewis base complexes were synthesized and fully characterized by FT-IR, 1H, 13C-NMR, elemental analysis and CI/FAB-MS. Several X-ray single crystal structures were determined. The crystal structure of methyl(5,5’-di-ethoxycarbonyl-2,2’-bipyridine)trioxorhenium displays a disorder with respect to the metal center. All the complexes are applied as homogeneous epoxidation catalysts with H2O2 (or TBHP in the case of MoO2Cl2·L2) as oxidizing agent. In general, MTO-Schiff base and MTO / MoO2Cl2 bidentate Lewis base complexes show a better catalytic activity towards cyclooctene epoxidations in comparison to MTO-salen complexes. In the case of MTO-salen complexes, an asymmetric epoxidation reaction using the prochiral trans-ß-methylstyrene as substrate was performed. Despite the reaction gives more than 90% yield, the enantiomeric execess (ee) is quite low (ca. 10%).The steric and electronic effects caused by the functional groups on the ligands play important roles on adduct formation, stability and catalytic performance with respect to different types of examined complexes. It was found that bis-MTO complexes show an disproportionately high catalytic activity as compared to mono-MTO complexes, due to the presence of a second MTO molecule, not only reacting as a second catalytic center, but also as a strongly electron withdrawing moiety on the ligand. Given the ready availability and stability at room temperature of the examined complexes, together with the good catalytic activity and high selectivity towards the formation of epoxides, they are good alternatives as epoxidation catalysts.
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In this work, (N-salicylidene) aniline and ((2-hydroxynaphtalen-1-yl)methylene) aniline derived MTO-Schiff base complexes, mono- and bis- MTO-salen complexes, bipyridine derived MTO-Lewis base and MoO2Cl2-Lewis base complexes were synthesized and fully characterized by FT-IR, 1H, 13C-NMR, elemental analysis and CI/FAB-MS. Several X-ray single crystal structures were determined. The crystal structure of methyl(5,5’-di-ethoxycarbonyl-2,2’-bipyridine)trioxorhenium displays a disorder with respect t...
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