Dearomatization of Anilines by Coordination to Pentaammineosmium(II)

Abstract

η2-Aniline complexes of the π-base pentaammineosmium(II) are synthesized with a variety of different aniline ligands in good yield. Once synthesized, these complexes display ligand-based reactivity with a variety of electrophiles. Reaction with trifluoromethanesulfonic (triflic) acid produces 2H- and 4H-anilinium complexes, species resulting from protonation on the ring. The regioselectivity of protonation depends on a variety of factors, including the aniline substitution pattern, temperature, and solvent. In addition, the η2-aniline complexes undergo regiospecific, chemospecific, and stereospecific reactions with carbon electrophiles such as Michael acceptors, acetals, and ketals. The resulting anilinium complexes are stabilized by a strong metal-to-ligand back-bonding interaction. As a result, these 4H-anilinium complexes may be functionalized further by their reaction with nucleophiles and complete dearomatization of the aniline ligand is thus achieved. The resulting allylamine and imine complexes are...