The decarbonylation of [RE(2)(CO)(10)] on ultrathin MgO(111) films (similar to 50 Angstrom) grown on a Mo(110) substrate was investigated with infrared reflection-absorption spectroscopy and temperature-programmed desorption/decomposition. When [Re-2(CO)(10)] was adsorbed at 320 K, it reacted with MgO(111) surface, forming a rhenium subcarbonyl, [Re(CO)(4){OMg}](2), where {OMg} represents oxygen on the MgO(111) surface. Upon heating to temperatures >400 K, [Re(CO)(4){OMg}](2) was decarbonylated, forming [Re(CO)(3){OMg}(3)]. Further heating to temperatures >600 K induced the formation of rhenium metal clusters. When it was adsorbed at 110 K, [Re-2(CO)(10)] condensed on MgO(111), with a fraction of the first layer decomposing to form [Re-(CO)(4){OMg}](2). In temperature-programmed desorption experiment, [Re-2(CO)(10)] multilayers desorbed at 295 K. An unidentified rhenium carbonyl species, probably rhenium pentacarbonyl, desorbed at 350 K. The CO stretching frequencies of the rhenium subcarbonyls were dependent on the coadsorption of water. The infrared spectra show that the symmetry of the surface-bound rhenium tricarbonyls is C-3v. The results are among the first characterizing the adsorption of metal complexes on well-defined metal oxide surfaces, and they demonstrate the value of structurally characterized supports for elucidation of the nature of the metal-support interface.