Carbon—Metal Hydrogen Interchange in Organometal Clusters of Ruthenium and Osmium

Facile carbon-metal hydrogen exchange is demonstrated by the scrambling of deuterium into the hydrocarbon ligand from the hydride position of (μ-H)(μ₃-η³-CH₃CH₂C═C═C(H)CH₃)Os₃(CO)₉ (I) at 110 °C in a sample initially 80% enriched in deuterium at the hydride position by ¹H NMR techniques. Deuterium was incorporated into the allenic hydrogen position and the methylene hydrogens but not into the methyl groups. The observed scrambling is interpreted in terms of reversible formation of a 46e alkyne complex (μ₃-η2-Ch₃Ch2C≡Cch2Ch3)Os3(CO)₉. The analogous ruthenium complex I' was also deuteriated in the hydride position (76%), and the scrambling of deuterium was observed by ¹H NMR during its isomerization to the corresponding allylic isomer (μ-H)(μ3-η3-Ch3Ch₂C═C(H)═CCH₃)Ru₃(CO)₉ (II). A scrambling pattern similar to that seen for I is observed. These results are considered in terms of the known differences in the ligand dynamics of the organic ligands in structural types I and I', and a two-step mechanism is proposed for the isomerization of I' to II.