A well-defined supported metal catalyst : Ir4/MgO

[Ir4(CO)12] was used as a precursor for the preparation of a MgO-supported catalyst with a uniquely simple metal structure, Ir4. The precursor was adsorbed on MgO from hexanes with the metal framework remaining intact, as determined by extended X-ray absorption fine structure (EXAFS) spectra. The surface-bound species was inferred to be predominantly [HIr4(CO)11]−, which could be extracted from the surface by cation metathesis and identified in solution by infrared spectroscopy. After treatment of the MgO-supported iridium carbonyl in He followed by H2 at 300 °C, the sample was characterized again by EXAFS spectroscopy; the results provide evidence that the predominant surface species are clusters of four Ir atoms with an average Ir-Ir distance of 2.69 A.