Probing Metal Oxide Surface Reactivity with Adsorbate Organometallic Chemistry: Formation of Iridium Carbonyl Clusters on γ-Al2O3

[Ir 8 (CO) 22 ] 2 - was formed by surface-mediated synthesis by treatment of [Ir(CO) 2 (acac)] supported on uncalcined γ-Al 2 O 3 under 1 atm of CO at room temperature. The formation of [Ir 8 (CO) 22 ] 2 - completes the synthesis of a family of iridium carbonyl clusters, including [Ir 4 (CO) 12 ], [HIr 4 (CO) 11 ] -, [Ir 6 (CO) 15 ] 2 -, and [Ir 8 (CO) 22 ] 2 -, on the surface of γ-Al 2 O 3 . The surface chemistry parallels known solution chemistry of the synthesis of the family of iridium carbonyls. The products formed are controlled largely by the basicity of the solution or surface, and the analogy between the solution and surface chemistry provides a preliminary, qualitative basis for characterizing the basicity of γ-Al 2 O 3 and other metal oxide samples. Decarbonylation of [Ir 8 (CO) 22 ] 2 - on γ-Al 2 O 3 led to nearly uniform tetrahedral Ir 4 clusters; it is likely that the Ir−Ir single bond linking two iridium tetrahedral moieties in the precursor [Ir 8 (CO) 22 ] 2 - on γ-Al 2 O 3 was broken during the decarbonylation.