Direct observation of .eta.2-arene complexes of [(C5Me5)Rh(PMe3)

Abstract

Over the past few years, there has been substantial progress in studies of the mechanism of activation of aliphatic aromatic C-H bonds by transition metals. In particular, earlier studies in the authors group have indicated that arenes coordinate to ((Ce{sub 5}Me{sub 5})Rh(PMe{sub 3})) in an {eta}{sup 2} fashion prior to C-H bond oxidative addition, and that this initial coordination permits the activation of aromatic C-H bonds to compete with aliphatic C-H bond activation. The evidence for {eta}{sup 2}-arene coordination relies heavily on indirect experiments (intramolecular isomerization of an aryl deuteride, kinetic isotope effect experiments), as the only direct evidence for arene coordination was with p-di-tert-butylbenzene at low temperature. They report here the room temperature observation of {eta}{sup 2}-arene complexes of ((C{sub 5}Me{sub 5})Rh(PMe{sub 3})) and an equilibrium between and {eta}{sup 2}-arene complex and its aryl hydride counterpart.