C−H Bond Activation by Rhodium(I) Phenoxide and Acetate Complexes: Mechanism of H−D Exchange between Arenes and Water

New rhodium(I) complexes (PNP)Rh(X) (PNP = 2,6-bis(di-tert-butylphosphinomethyl)pyridine) (X = OTf (1), OAc (3), OH (8), OCH2CF3 (9), OC6H5 (10), OC6H4NO2 (11)) have been prepared. Hydroxide complex 8 and trifluoroethoxide complex 9 undergo stoichiometric activation of benzene-d6 to form the phenyl complex (PNP)Rh(C6D5). Acetate and aryloxide complexes 3, 10, and 11 are active catalysts for H−D exchange between arenes and water. Control experiments indicate that the rhodium complexes are the active catalysts and that the observed exchange is not catalyzed by adventitious acid. Mechanistic studies of the H−D exchange reaction support a pathway involving dissociation of aryloxide or acetate ligand. The reaction is accelerated by added alcohol and, for the acetate complex, inhibited by added sodium acetate.