DEAROMATIZATION OF ANILINES BY COORDINATION TO PENTAAMMINEOSMIUM(II)

eta(2)-Aniline complexes of the pi-base pentaammineosmium(II) are synt hesized with a variety of different aniline ligands in good yield. Onc e synthesized, these complexes display ligand-based reactivity with a variety of electrophiles. Reaction with trifluoromethanesulfonic (trif lic) acid produces 2H- and 4H-anilinium complexes, species resulting f rom protonation on the ring. The regioselectivity of protonation depen ds on a variety of factors, including the aniline substitution pattern , temperature, and solvent. In addition, the eta(2)-aniline complexes undergo regiospecific, chemospecific, and stereospecific reactions wit h carbon electrophiles such as Michael accepters, acetals, and ketals. The resulting anilinium complexes are stabilized by a strong metal-to -ligand back-bonding interaction. As a result, these 4H-anilinium comp lexes may be functionalized further by their reaction with nucleophile s and complete dearomatization of the aniline ligand is thus achieved. The resulting allylamine and imine complexes are oxidatively removed from the metal center to provide organic allyl amine and cyclohexenone products in moderate yield. This methodology is complementary to that based on eta(6)-complexation of an electron-deficient metal center to the aniline.