Molecular Dynamics of Mixed-Metal Clusters. Carbon-13 and Hydrogen-1 NMR Studies of H₂FeRu₃(CO)₁₃, H₂FeRu₂Os(CO)₁₃, and H₂FeRuOs₂(CO)₁₃

Variable-temperature ¹H and ¹³C NMR spectra of H₂FeRu₃(CO)₁₃, H₂FeRu₂Os(CO)₁₃, and H₂FeRuOs₂(CO)₁₃ have been measured and interpreted in view of three distinct fluxional processes. In the lowest temperature process the bridging and terminal carbonyls bound to Fe undergo localized exchange. The second process involves migration of the carbonyls around the face of the tetrahedral cluster that contains the bridging carbonyls. The highest temperature process involves a subtle reorganization of the metal framework. This latter process accounts for interconversion of the two enantiomers of the Q isomer of H₂FeRu₂Os(CO)₁₃ and H₂FeRuOs₂(CO)₁₃ and allows for the Cs ⇄ C₁, isomerization. Line-shape analysis of the ¹H NMR spectra and comparison of the ¹³C NMR spectra show that the activation barrier for each process increases as the Os content of the cluster increases.