Carbon-carbon bond formation promoted by organoruthenium complexes. The first unsubstituted π-metallabenzene complex, Cp*₂Ru₂(n²:n⁵-C ₅H₅)(SiMe₃), and synthesis of the tetramethyleneethane complex Cp*₂Ru₂(n³:n³-C ₆H₈)Cl₄

Treatment of the methylene/silyl complex Cp*₂Ru₂(μ-CH₂)(SiMe ₃)(μ-Cl) with ethyne in toluene gives several products resulting from carbon-carbon bond coupling reactions; these include the first unsubstituted π-metallabenzene complex, Cp*₂Ru₂(n²:n⁵-C ₅H₅)(SiMe₃), 1, the arene complex [Cp*Ru(n⁶-C₆H₆)]Cl, 2, and the bridging metallacyclopentadiene complex Cp*₂Ru₂(n²:n⁴-C ₄H₄)Cl₂,3. Treatment of [Cp*RuCl₂]₂ with propadiene also leads to a carbon-carbon bond coupling reaction, and the product is the tetramethyleneethane (i.e., 2,2'-biallyl) complex Cp*₂Ru₂(n³:n³-C ₆H₆)Cl₄, 4. A single-crystal X-ray diffraction study of 1 shows that the metallabenzene ring is π-bonded to a second metal center and that the trimethylsilyl group is a terminal ligand on the ruthenium center that lies in the metallabenzene ring plane. The aromaticity of the metallabenzene ring in 1 is also discussed.