Synthesis and Property of Diruthenium Complexes Containing Bridging Cyclic Diene Ligands and the Reaction of Diruthenium Tetrahydrido Complex with Benzene Forming a μ-η²:η²-Cyclohexadiene Complex via Partial Hydrogenation on a Ru₂ Center

The syntheses, structures, and reactivities of diruthenium complexes having a five-, six-, and seven-membered cyclic diene ligands are discussed in this paper. While the μ-η²:η²-cyclohexadiene complex 3 was readily prepared by the reaction of the diruthenium tetrahydrido complex 1 with 1,3-cyclohexadiene, 3 was alternatively synthesized by the reaction of 1 with benzene via partial hydrogenation of benzene on a diruthenium plane. While the μ-η²:η²-cyclohexadiene ligand was liberated as benzene upon mild heating, the treatment of 3 with ^tBuNC and CO caused further migration of hydrido ligand to the C₆ moiety to yield the μ-η²-cyclohexenyl complex 6 and the μ-cyclohexylidene complex 8, respectively. The reactions of 1 with cyclopentadiene and cycloheptatriene also afforded the bridging cyclic diene complexes 10 and 11. While the thermolysis of the μ-η²:η²-cyclopentadiene complex 10 resulted in the degradation of the cluster skeleton forming Cp*RuCp (12), the μ-η²:η²-cycloheptadiene complex 11 was stable upon heating. These differences can be attributed to the aromatization of the cyclic diene moiety.