The mechanisms for the interconversion of facial diastereomers of a variety of TpRe(CO)(L)(eta (2)-LAr) complexes {L = (BuNC)-Bu-t, pyridine (py), PMe3, or 1-methylimidazole (MeIm); L-Ar = benzene, anisole, naphthalene, 1-methylpyrrole, furan, or thiophene; Tp = hydridotris(pyrazoly l)borate} have been investigated by H-1 NMR spin saturation experiments. In addition, the rates and free energies of activation for these processes were calculated from spin saturation experiments and T-1 measurements. The operative mechanisms for interconversion of the pi diastereomers were found to be nondissociative, undergoing either an interfacial or intrafacial linkage isomerization. A comparison of the kinetic parameters for isomerization of related eta (2)-olefin complexes of the {TpRe(CO)(PMe3)} and {CpRe(NO)(PPh3)}(+) fragments is also presented.