13C-enriched Fe3(CO)12 and Ru3(CO)12 supported on a variety of metal oxide surfaces (γ-Al2O3, SiO2, MgO, and HNa-Y zeolite) have been examined by carbon-13 “magic-angle” sample-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Our results show that the γ-Al2O3-supported Fe3(CO)12 cluster is fluxional at room temperature, but low-temperature spectra give no evidence in favor of the unusual bridging carbonyl proposed previously by some workers from infrared (IR) spectroscopy. On HNa-Y, Fe3(CO)12forms a highly mobile chemisorbed species, and the 13C chemical shift is consistent with formation of the dianion [Fe3(CO)11]2-. For Ru3(CO)12 on γ-Al2O3 and SiO2 surfaces, our results are in agreement with IR studies and show that, under anaerobic conditions, highly mobile physisorbed clusters are initially formed. Upon exposure to air or upon thermal activation, divalent tricarbonyl species are generated. The resonances of these chemisorbed species are enhanced by cross polarization and display large chemical shift anisotropies, due to restricted mobility. On MgO, Ru3(CO)12 behaves quite differently, the13C NMR results being consistent with the formation of highly fluxional hexaruthenium carbonyl clusters.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry