Kinetic Site of Protonation in Transition Metal Clusters and Its Possible Relationship to Large Kinetic Deuterium Isotope Effects in Hydrogen Transfer Processes

Abstract

The protonation of Ru3(CO)10(μ-NO)- (1) has been reexamined using CF3CO2X and CF3SO3X (X = H or D) in the temperature range of −80 to +25 °C using 13C NMR techniques. For both acids, the kinetic site of protonation is the oxygen of the nitrosyl group, giving Ru3(CO)9(μ3-CO)(μ3-NOH) (2). The rate of proton transfer to the metal core, to give Ru3(CO)10(μ-NO)(μ-H) (3), is approximately the same for both the protic and deuterated cases. These results are contrasted with previous proton transfer studies of other metal clusters which exhibit anomalously large kinetic deuterium isotope effects, and it is tentatively concluded that these effects are associated with strictly intramolecular hydrogen transfer as opposed to the anion-assisted intermolecular process reported here. The carbonyl group ligand dynamics for 1−3 are reported.