the same type of structure (Fig. 2) for the anion 2 as mentioned above for the case of the molybdenum compounds. The oxygen atom bridges all three titanium atoms and each pair of Ti atoms is linked via a side-on coordinated disulfide unit. The Ti-Ti distances of 314 to 318 pm are markedly greater than the Mo-Mo distances in the molybdenum clusters-as to be expected for a Ti'" compound, [**I Hetero n-Systems, Part 15. This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen 1ndustrie.-Part 14: [S]. Angew. Chem. Inr. Ed. Engl. 27 11988) No. 2 0 VCH Verlogsgesellschqfr mbH, 0-6940 Weinheim, 1988 0570-0833/88/0202-0295 $ 02.50/0
Synthesis of 3-Nitro-l,l-bis(triisopropyIsilyI)-l~-cyc~opropabenzene and Derivatives of Azocyclopropabenzene I , l-Bis(triisopropylsilyl)-l~-cyclopropaben~ene (4) can be nitrated at C(3) without opening of the threemembered ring. Further functionalized cyclopropabenzenes are available in this way. Das 1 H-Cyclopropabenzol (1) und seine Derivate reagieren mit Elektrophilen und Protonenduren unter Offnung des dreigliedrigen Ringes zu Toluol-Derivaten (Schema I), so dass elektrophile Substitutionsreaktionen am aromatischen Ring in dieser Verbindungsklasse bisher nicht beschrieben wurden [I] [2].
Für π‐Elektronendelokalisierung im Benzolring trotz Anellierung eines Cyclopropenrings sprechen die röntgenographisch bestimmten Strukturen der Titelverbindungen 1a und 1b. Darüber hinaus findet man in beiden trotz der sehr sperrigen Substituenten von 1b praktisch gleiche Bindungslängen und ‐winkel. Das Cyclopropabenzolgerüst ist in beiden Verbindungen nicht planar, wobei sich‐ aus sterischen Gründen – die Art der Symmetrieerniedrigung in 1a und 1b unterscheidet.
The disilyl derivative (IV) which is prepared from (I) via the unstable intermediate (III) is nitrated without opening of the three‐membered ring to afford the title compound (V).
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