The Regio- and Stereospecific Selective Hydrogenation of η2-Coordinated Arenes

Abstract: Several Abound arene complexes of pentaammineosmium(II) have been selectively hydrogenated to alkene products

in the presence of a heterogeneous catalyst (Pd, Rh). In all cases the coordinated osmium was shown both to activate the

arene ligand toward catalytic hydrogenation and to protect the alkene product toward further reduction. Hydrogenation can

be achieved both regio- and stereoselectivity and is shown to occur exclusively anti to the metal center. The structure of the

3-methoxycyclohexene complex [0s(NH3)5(j)2-C7H120)](0Tf)2 has been determined. The hydrogenation of eta2-bound anisóle

or 1,4-dimethoxybenzene is not concerted; the semihydrogenation product, a vinyl ether, rapidly hydrolyzes in acid medium

to form a cyclohexenone complex.