Facile Hydrogenation of Acenapthylenes and Azulenes on the Face of a Triruthenium Carbonyl Moiety: Discovery of Specific Reactions on the Cluster Framework Providing Unique Insight for Cluster Catalysis

Summary.

 Activation of molecular hydrogen by triruthenium carbonyl clusters bearing acenaphthylene or aceanthrylene as the face-capping ligand results in partial hydrogenation of these polyaromatic ligands, giving the corresponding hydride carbonyl clusters bound to hydrogenated acenaphthylene or aceanthrylene. The first isolation of 4,5-dihydroacenaphthylene or 4,5-dihydroaceanthrylene was achieved by treatment of the resulting hydride carbonyl clusters with CO. Similarly, triruthenium carbonyl species bearing substituted azulenes as the face-capping moiety gives the corresponding hydride carbonyl cluster bearing partially hydrogenated azulenes at room temperature; the corresponding partial hydrogenation of azulenes does not occur with di- or tetraruthenium homologues. Hydrogenation of di-, tri-, and tetraruthenium carbonyl clusters bearing substituted azulenes at elevated temperatures furnishes hydrogenative cluster fragmentation to mononuclear ruthenium hydrides; the stereochemistry of these complexes suggests that the reaction takes place through the activation of H₂ by the multinuclear species. The roles of the acenaphthylene or azulene ligands as hemilabile μ₃-ligands for triruthenium carbonyl clusters are discussed.