Allylic amination of unactivated olefins by nitroarenes, catalyzed by ruthenium complexes. A reaction involving an intermolecular C-H functionalization

A reaction is reported, resulting in the allylic amination of an unactivated olefin, cyclohexene, by a nitroarene, catalyzed by Ru-3(CO)(12)/Ar-BIAN (Ar-BIAN = bis(arylimino)acenaphthene), under CO pressure. The reaction involves an intermolecular catalytic C-H functionalization by a transition metal complex. Best results (selectivity up to 81.9%, with a substrate/Ru-3(CO)(12) ratio = 50) are obtained by using nitroarenes bearing electron-withdrawing substituents and Ph-BIAN as a ligand. Other olefins can also be employed in place of cyclohexene. The reaction mechanism has been investigated. The reaction is first order in nitroarene and olefin, which is used as solvent in most cases, but the rate equation also contains an olefin-independent term. A rate acceleration by small amounts of toluene in the solvent mixture is due to a faster formation of Ru(CO)(3)(Ar-BIAN) from Ru-3(CO)(12) and Ar-BIAN in its presence. This last complex is in equilibrium with the active species Ru(Ar-BIAN)(CO)(2)(cyclohexene), and its direct reaction with the nitroarene accounts for the olefin-independent term in the rate law. The reaction of Ru(CO)(3)(Ar-BIAN) with nitroarenes gives Ru(CO)(2)(Ar-BIAN)(eta(2)-ArNO), which has been isolated in one case, but this complex is not an intermediate in the synthesis of allylamines. Coupling between a coordinated nitrosoarene and a coordinated olefin appears to be responsible for the C-N bond formation.