Bidentate Lewis base adducts of molybdenum(VI): Ligand impact on catalytic performance and stability

Abstract

The reaction of solvent substituted [MoO 2Cl 2] (THF) 2 complexes with 1 equiv. of bidentate nitrogen donor ligands leads to complexes of the type [MoO 2Cl 2L 2] (L 2 = 4,5-diazafluorene-9-one; 1,10-phenanthroline-5,6-dione; 2,2′-biquinoline-4,4′-dicarboxylic acid, diethyl ester; 3,6′-bis-2-pyridyl-pyridazine; 4,4′-di-ethoxycarbonyl-2,2′-bipyridine) in quantitative yields at room temperature under inert gas atmosphere within a few minutes. The catalytic activity of the [MoO 2Cl 2L 2] complexes in olefin epoxidation with t-butyl hydroperoxide as oxidizing agent is strongly influenced by the nature of the ligand L and its steric demand. The complexes, with the sole exception of compound 9 [MoO 2Cl 2(1,10-phenanthroline-5,6-dione)], are very active and highly selective epoxidation catalysts. The influence of the terminal oxo ligands together with the Lewis base ligands on the Mo center obviously keeps the compounds on a quite stable level of electron density.