ChemInform Abstract: Homogeneous Catalysis on Metal Clusters. The Isomerization and Selective Hydrogenation of Dienes, Alkenes, and Alkynes in the Presence of [(η-C 5 H 5 )NiOs 3 (μ-H) 3 (CO) 9 ] and [(η-C 5 H 5 )NiOs 3 (μ-H) 3 (CO) 8 L] (L: PPh 2 H or P(C 6 H