Synthesis and Property of Diruthenium Complexes Containing Bridging Cyclic Diene Ligands and the Reaction of Diruthenium Tetrahydrido Complex with Benzene Forming a μ-η<sup>2</sup>:η<sup>2</sup>-Cyclohexadiene Complex via Partial Hydrogenation on a Ru<sub>2</sub> 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-η<sup>2</sup>:η<sup>2</sup>-cyclohexadiene complex <b>3</b> was readily prepared by the reaction of the diruthenium tetrahydrido complex <b>1</b> with 1,3-cyclohexadiene, <b>3</b> was alternatively synthesized by the reaction of <b>1</b> with benzene via partial hydrogenation of benzene on a diruthenium plane. While the μ-η<sup>2</sup>:η<sup>2</sup>-cyclohexadiene ligand was liberated as benzene upon mild heating, the treatment of <b>3</b> with <sup>t</sup>BuNC and CO caused further migration of hydrido ligand to the C<sub>6</sub> moiety to yield the μ-η<sup>2</sup>-cyclohexenyl complex <b>6</b> and the μ-cyclohexylidene complex <b>8</b>, respectively. The reactions of <b>1</b> with cyclopentadiene and cycloheptatriene also afforded the bridging cyclic diene complexes <b>10</b> and <b>11</b>. While the thermolysis of the μ-η<sup>2</sup>:η<sup>2</sup>-cyclopentadiene complex <b>10</b> resulted in the degradation of the cluster skeleton forming Cp*RuCp (<b>12</b>), the μ-η<sup>2</sup>:η<sup>2</sup>-cycloheptadiene complex <b>11</b> was stable upon heating. These differences can be attributed to the aromatization of the cyclic diene moiety.