Benzimidazolic complexes of methyltrioxorhenium(VII): Synthesis and application in catalytic olefin epoxidation

Seven new Lewis base adducts of methyltrioxorhenium(VII) (MTO) with the general formula CH₃ReO₃·L (L = bidentate benzimidazolic ligands, namely (L = 2-(2-Pyridinyl)-1H-benzimidazole, 5-methyl-2-(2-pyridyl)benzimidazole, 5-Chloro-2-(2-pyridyl)benzimidazole, 2-(2-Pyridyl)-1H-imidazo-[4,5-b]-pyridine, 2-(2-Quinolyl)benzimidazole, 2-(5-methyl-1H-benzimidazol-2-yl)-quinoline, and 2-(5-chloro-1H-benzimidazol-2- yl)-quinoline)) were prepared. All the complexes were characterized by IR, ¹H, ¹³C NMR, MS and elemental analysis as well as tested as catalysts for olefin epoxidation using 35% aqueous hydrogen peroxide as oxidant under mild condition. The influence of different ligand concentrations was also examined. The results show that the complexes are highly selective in olefin epoxidation and good yields can be obtained when excess ligand is applied.