Reactions of Conjugated Dienes with a Triruthenium Hydrido Carbonyl Cluster: Synthesis and Reactivity of Trinuclear Derivatives Having an Edge-Bridging Allyl Ligand

The reactions of the hydrido triruthenium complex [Ru3(μ-H)(μ3-κ2-HNNMe2)(CO)9] (1; H2NNMe2 = 1,1-dimethylhydrazine) with conjugated dienes give trinuclear derivatives that contain edge-bridging allyl ligands. The isolated allyl products are [Ru3(μ-κ3-C8H13)(μ3-κ2-HNNMe2)(μ-CO)2(CO)6] (2) from 1,3-cyclooctadiene, [Ru3(μ-κ3-C6H9)(μ3-κ2-HNNMe2)(μ-CO)2(CO)6] (4) from 1,3-cyclohexadiene, and [Ru3(μ-κ3-C4H6OMe)(μ3-κ2-HNNMe2)(μ-CO)2(CO)6] (5) from cis-1-methoxybutadiene. While the cyclic structure of the allyl ligands of 2 and 4 forces these ligands to have an anti-anti arrangement, compound 5 contains an anti-MeO-syn-Me allyl ligand. This synthetic approach, which uses conjugated dienes as precursors to allyl ligands, represents an alternative to the use of alkynes having α-hydrogen atoms as precursors to allyl ligands, especially if the alkyne required to make a particular allyl ligand is unknown or difficult to obtain, as happens for cyclic alkynes. The cyclooctenyl derivative [Ru3(μ-κ2-C8H13)(μ3-κ2-HNNMe2)(μ-CO)2(CO)6] (3) has also been obtained, as a minor product, from the reaction of 1 with 1,3-cyclooctadiene. A study of the reactivity of compound 2 has been performed. It undergoes protonation at the metal atoms to give the cationic derivative [Ru3(μ-H)(μ-κ3-C8H13)(μ3-κ2-HNNMe2)(μ-CO)2(CO)6]+, which has an edge-bridging hydrido ligand and has been isolated as the [BF4]− salt (6). Hydride addition to compound 2 occurs at the allyl ligand to give uncoordinated cyclooctene. Treatment of 2 with tert-butylisocyanide leads to the CO-substitution derivative [Ru3(μ-κ3-C8H13)(μ3-κ2-HNNMe2)(tBuNC)(μ-CO)2(CO)5] (7), whereas its reaction with diphenylacetylene affords 1,3-cyclooctadiene and the 1,2-diphenylethenyl derivative [Ru3(μ-κ2-PhCCHPh)(μ3-κ2-HNNMe2)(μ-CO)2(CO)6] (8). Some of these results have been rationalized with the help of DFT calculations.