Silyl-Substituted Dilithium Salt of Fulvene Dianion with 6 Center/8 Electron π-System: Synthesis and Characterization

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  • Tsukasa Matsuo
    Department of Chemistry, University of TsukubaTsukuba, Ibaraki 305-8571
  • Akira Sekiguchi
    Department of Chemistry, University of TsukubaTsukuba, Ibaraki 305-8571
  • Hideki Sakurai
    Department of Industrial Chemistry, Faculty of Science and Technology, Science University of TokyoNoda, Chiba 278-8510

説明

<jats:title>Abstract</jats:title> <jats:p>Treatment of fulvene derivatives bridged by Me2Si–X–SiMe2 chains (2a : X = CH2, 2b : X = O) with lithium metal in THF yields yellow crystals of the dilithium salt of fulvene dianion (3a and 3b) with 6 center/8 electron π-system. The molecular structure of the dianion dilithium 3a has been established by X-ray crystallography. The dianion dilithium 3a has a monomeric structure and forms a contact ion pair (bis-CIP) in the crystal. One of the lithium atoms is located above the center of the five-membered ring by η5-coordination, whereas the other one is bonded to the exo-cyclic carbon atom by η2-coordination. The structural parameters of 3a are discussed in comparison to those of the neutral starting molecule 2a. The structure of 3a in solution has also been discussed on the basis of NMR spectroscopic data. The two lithium ions of 3a are not fixed to the π-skeleton in toluene-d8, but are fluxional, giving a highly symmetrical bis-CIP structure. The spectral data in THF-d8 at 298 K also suggest the bis-CIP structure of 3a. However, the lithium ion on the five-membered ring is dissociated to yield an ion pair (CIP-SSIP) at low temperature in THF-d8, and two dianion species (bis-CIP and CIP-SSIP) were found in THF-d8.</jats:p>

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