| Research Abstract |
Polycyclic aromatic compounds have a large pi-conjugated system on both sides of aromtic plane. In this study, we tried to collect and align transition-metal fragments by use of polycyclic aromatic compounds. Triphenylene, an 18 pi-electron aromatic compound, as a model for polycyclic arene compounds, reacts with Ru(1,5-COD) fragment to give mono-, di- and trinuclear clusters on the aromatic plane. Formation of the compound [Ru(1,5-COD)]_n(triphenylene)] (n = 1-3) indicates that triphenylene acts as a 6 pi, 12 pi and 18 pi donors and all pi electrons on the aromatic plane is able to donate to the ruthenium fragments. This is the first example for the formation of trinuclear complex on aromatic compounds. Treatment of Ru(1,5-COD)(η^6-triphenylene) with Ru(1,5-COD)(η^6-naphthalene) in the presence of MeCN as a Lewis base catalyst for the arene exchange reaction, gave a dinuclear complex [Ru(1,5-COD)]_2(μ^2-η^6:η^6-triphenylene). Hydrogenolysis of Ru(1,5-COD)(1,3,5-COT) in the presence of
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Ru(1,5-COD)(η^6-triphenylene) or [Ru(1,5-COD)]_2(μ^2-η^6:η^6-triphenylene) led to give a trinuclear complex [Ru(1,5-COD)]_3(μ^3-η^6:η^6:η^6-triphenylene). On the other hand, reaction of [Ru(1,5-COD)]_3(μ^3-η^6:η^6:η^6-triphenylene) with free triphenylene in the presence of MeCN gave mono- and dinuclear complexes. These facts show that the addition of Ru(1,5-COD) fragment to triphenylene ring is reversible.
Before we started this study, there is a limited numbers of procedures to give transition metal complexes having a polycyclic aromatic compounds. Therefore, we studied to develop an efficient route to give complexes having a polycyclic aromatic compound. During this study, we found that treatment of (1,5-cyclooctadiene)(1,3,5-cyclooctatriene)ruthenium(0) with polycyclic aromatic compounds in the presence of HPF_6 produced corresponding cationic complexes [Ru(η^6-polycyclic arene)(1-5-η^5-cyclooctadienyl)]PF_6 in good yields. Since these compounds reversibly exchanged their arene ligand in the presence of added arene, we studied thermodynamic stability of these polycyclic arene complexes. This study showed that acenes were more labile than aphenes. Based on these facts, we concluded that aromaticity of the uncoordinated ring governed stability of the arene complexes. Less
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