Complexes with late metal-oxygen and -nitrogen single bonds (metal alkoxides and amides) play important roles in biological systems and have been implicated as intermediates in a variety of industrially important catalytic reactions. 1-3 When the metal-heteroatom bond reacts with carbon-hydrogen bonds of organic molecules, an important question concerns whether the transformation takes place via odd-or even-electron intermediates. For example, many late metal alkoxides undergo rapid overall even-electron RO − transfer reactions with electrophiles. 4-8 In other cases, metal-oxygen bonds have been proposed to react by initial hydrogen atom abstraction, an odd-electron process. 9-11 Stimulated by this difference in behavior, we set out to determine the preferred mode of reactivity in the well-characterized parent hydroxo and amide complexes: trans-(DMPE) 2 (H)-Ru(NH 2 ) (1) and trans-(DMPE) 2 (H)Ru(OH) (2) (DMPE = 1,2-bis(dimethylphosphino) ethane). 8,12 This study has uncovered only 2-electron behavior for both the OH and NH 2 metal-bound fragments, and has revealed that complex 1 bears a surprisingly basic amido ligand, a property that is expressed without dissociation of the NH 2 group from the ruthenium center.In analogy to reactions reported by Stack and Mayer and their co-workers, 9,11 our ruthenium amido and hydroxido complexes 1 and 2 cause the dehydrogenation of cyclohexadiene (1,4-CHD) and 9,10-dihydroanthracene (DHA) (eq 1). However, compounds 1 and 2 also catalyze the interconversion of 1,4-and 1,3-CHD more rapidly (t 1/2 = <5 min) than dehydrogenation occurs.The dehydrogenation and isomerization reactions could proceed by initial abstraction of a hydrogen atom (although the required oxidation state change is less favorable here than in the earlier-reported systems) or a proton, in addition to pathways that might involve interaction of the diene with the metal center. To explore this question, we extended the above reactions to a larger series of organic compounds having C-H bonds characterized by a wide range of bond dissociation energies and acidities.Two interrelated modes of reactivity were observed with organic compounds containing relatively acidic C-H bonds (Scheme 1). The first includes the generation of a stable ion pair formed by overall proton transfer from carbon to ruthenium-bound nitrogen (e.g., 1 + fluorene → 4a in THF or benzene). 13 The second is overall displacement of the nitrogen fragment from