Synthesis and structural characterization of unsymmetrical osmocenes containing the pentamethylcyclopentadienyl ligand

Treatment of dibromo(pentamethylcyclopentadienyl)osmium(III) dimer with alkali metal salts of a variety of cyclopentadienyl derivatives provides a simple approach to the synthesis of unsymmetrical osmocenes containing the pentamethylcyclopentadienyl ligand. Furthermore, the reaction of dibromo(pentamethylcyclopentadienyl)osmium(III) with alkali metal salts of pyrrole and 3,5-di-tert-butylpyrazole afforded the corresponding pentamethylcyclopentadienylosmium complexes containing η5-pyrrolyl or η5-3,5-di-tert-butylpyrazolato ligands. This overall synthetic approach afforded pentamethylosmocene (64%), (η5-pentamethylcyclopentadienyl)(η5-indenyl)osmium (36%), (η5-pentamethylcyclopentadienyl)(η5-fluorenyl)osmium (30%), (η5-pyrrolyl)(η5-pentamethylyclopentadienyl)osmium (30%), and (η5-3,5-di-tert-butylpyrazolato)(η5-pentamethylcyclopentadienyl)osmium (38%). The new complexes were characterized by spectroscopic and analytical techniques, and by single crystal X-ray structural determinations. In the solid state, all of the new complexes exist as eclipsed metallocenes.