Hexabromotricyclobutabenzene and hexabromohexaradialene: their nickel-mediated one-pot syntheses and crystal structures.
The reaction of hexakis(dibromomethyl)benzene with [(Bu3P)2Ni(COD)] (COD = 1,5-cyclooctadiene) in DMF at 65-70 DegC yielded a mixt. of the title compds. The mixt. was sepd. by column chromatog. to yield hexabromotricyclobutabenzene (I) and hexabromohexaradialene (II) in 24 and 16% yields, resp. 1H and 13C NMR spectroscopy suggest that was obtained as the syn-all-trans isomer I, and the sym. anti-all-trans isomer was not obtained at all. The X-ray structures of I and II are reported. The hexaradialene II has a chair conformation, and deviates from planarity by 43.6 Deg. Heat or radical impurities cause the clean transformation of I to II.
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