Catalysis by supported clusters: two examples of catalytic reactions that involve a molecular cluster frame

Abstract
Two examples of catalysis by supported clusters are given that involve a molecular cluster frame during the catalytic cycle. (H)Os 3 (CO) 10 (OSi^) is able to hydrogenate ethylene between 343 and 373 K. The mechanism of this reaction, which involves the molecular cluster frame, requires the opening of the bridging three-electron oxygen ligand as the key step of the catalytic process. Rh 6 (CO) 16 adsorbed on alumina is a catalyst for the water-gas shift reaction carried out between 293 and 393 K. The mechanism of this reaction involves three steps: (i) electrophilic attack by surface protons on the metallic frame with formation of Rh I (CO) 2 and Rh III (H) (H) species; (ii) reductive elimination of H 2 favoured by CO coordination to the Rh III (H) (H) species; (iii) nucleophilic attack by molecular water on CO coordinated to Rh I with regeneration of the starting cluster, release of CO 2 and surface protons.