KINETIC DEUTERIUM-ISOTOPE EFFECTS ON LIGAND MIGRATIONS IN METAL-HYDRIDES .2.

Variable-temperature (VT)1H and13C NMR studies of the complexes (µ-X)2OS3(CO)9(µ3-η2-(CH3CH2)2C2) (X = H or D) reveal that alkyne migration over the face of the cluster is directly linked to hydride migrations on the metal core as evidenced by a temperature-independent isotope effect (kHH/kDD = 1.7). In a related study of the VT13C NMR of (µ-x)2M3(CO)9(µ3-S) (X = H or D; M = Ru, Os) the observation of a kHH/kDD = 1.6 for both the osmium and ruthenium complexes demonstrates that the first stage of carbonyl averaging is brought about by hydride migration and not axial‒radial exchange of carbonyl groups, a process that occurs only at higher temperatures. The mechanistic implications of these results are discussed in the context of the reactivity of metal clusters and the dynamic properties of the metal‒hydrogen bond. © 1990, American Chemical Society. All rights reserved.