Reaction of disilagermirenes with phenylacetylene: from a germasilene -Ge=Si- to a metalladiene of the type -Si=Ge-C=C-

The reaction of tetrakis[di-tert-butyl(methyl)silyl]-2-disilagermirene (1b) with phenylacetylene at room temperature produced highly air- and moisture -sensitive bright orange crystals of 1, 1,2,3-tetrakis[di-tert-butyl(methyl )silyl]-4-phenyl-1,2-disila-3-germacyclopenta-2,4-diene (2b), which represe nts a previously unknown metalladiene with one Si=Ge and one C=C double bon d. The crystal structure of 2b was determined by X-ray crystallography, whi ch showed a trans-bent configuration around the Si=Ge double bond with a bo nd length of 2.250(1) Angstrom. The reaction mechanism to form 2b, the ques tion of conjugation of the two double bonds in a cyclopentadiene ring of 2b , as well as its reactivity are discussed. The reaction of tetrakis[di-tert -butyl(methyl)silyl]-1-disilagermirene (1a), which is an isomer of 1b, with phenylacetylene is also examined. (C) 2001 Elsevier Science B.V. All right s reserved.