STRUCTURE OF A CUMULENE BEARING BULKY SUBSTITUENTS - X-RAY STUDY OF 1,1,4,4-TETRAKIS(TRIMETHYLSILYL)BUTATRIENE

The structure of cumulene bearing bulky substituents, 1,1,4,4-tetrakis(trimethylsilyl)butatriene, has been determined by an X-ray diffraction method. The molecule is centrosymmetric, and the variation in carbon-carbon double bonds has been observed. The distance of the central C=C bond is 1.276(8) Å, whereas that of the terminal C=C bond is 1.319(6) Å. These bond lengths are very similar to the unsubstituted butatrienes and the influence of bulky trimeth-ylsilyl groups is not recognized in this context. Some distortions have been observed in the bond angles concerning the trimethylsilyl groups; the overcrowded environment of the central C=C bond seems to make this less reactive. © 1989 The Chemical Society of Japan.