Bidentate Lewis Base Adducts of Methyltrioxidorhenium(VII): Ligand Influence on Catalytic Performance and Stability

Methyltrioxidorhenium (MTO) forms 1:1 adducts of the general formula CH3ReO3·L2 with bidentate Lewis bases (L2 = 5,5′‐dimethyl‐2,2′‐bipyridine, 5,5′‐diamino‐2,2′‐bipyridine, 4,4′‐dibromo‐2,2′‐bipyridine, 5,5′‐dibromo‐2,2′‐bipyridine, diethyl 2,2′‐bipyridine‐5,5′‐dicarboxylate, 1,10‐phenanthroline‐5,6‐dione, 3,6‐di(2‐pyridyl)pyridazine). Due to the steric demands of the ligands, the complexes display a distorted octahedral geometry as confirmed by solid state X‐ray crystallography. The rhenium center is disordered in all examined crystal structures. The complexes synthesized are thermally stable but sensitive to light and moisture. The 2,2′‐bipyridine derived complexes exhibit good catalytic activities for cyclooctene epoxidation in a biphasic H2O2/organic solvent catalytic system using hydrogen peroxide as oxidizing agent. The functional groups on the bipyridine rings play an important role with respect to the differences in formation, stability and activity of the complexes. Their influence depends largely on their electron donor capabilities. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) CH3ReO3 (MTO) forms adducts with bidentate Lewis bases. The formation, stability and catalytic activity of the complexes depend on the functional groups attached to the Lewis base ligands.