Dissociation of the Disilatricyclic Diallylic Dianion [(C4Ph4SiMe)2]−2 to the Silole Anion [MeSiC4Ph4]− by Halide Ion Coordination or Halide Ion Nucleophilic Substitution at the Silicon Atom

Abstract

The reductive cleavage of the Si-Si bond in 1,1-bis(1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadiene) [(C4Ph4SiMe)2] (1) with either Li or Na in THF gives the silole anion [MeSiC4Ph4]− (2). The head-to-tail dimerization of the silole anion 2 gives crystals of the disilatricyclic diallylic dianion [(C4Ph4SiMe)2]−2 (3). The derivatization of 3 (crystals) with bromoethane (gas) under reduced pressure provides [(MeSiC4Ph4Et)2] (4) quantitatively. The reverse addition of 3 in THF to trimethylsilyl chloride, hydrogen chloride, and bromoethane in THF gives 1-methyl-1-trimethylsilyl-1-silole [Me3SiMeSiC4Ph4] (6), 1-methyl-2,3,4,5-tetraphenyl-1-silacyclo-3-pentenyl-1-methyl-1-silole [C4Ph4H2SiMe-MeSiC4Ph4] (7), and 1-methyl-2,5-diethyl-2,3,4,5-tetraphenyl-1-silacyclo-3-pentenyl-1-methyl-1-silole [C4Ph4Et2SiMe-MeSiC4Ph4] (8), respectively. The reaction products unambiguously suggest that the silole anion [MeSiC4Ph4]− is generated by coordination of the chloride ion at the silicon atom in 3 or by the nucleophilic substitution of either chloride or bromide ion at one of two silicon atoms in 3. The quenching reaction of 3 dissolved in THF with water gives 1,2,3,4-tetraphenyl-2-butene, the disiloxane of 1-methyl-2,3,4,5-tetraphenyl-1-silacyclo-3-pentenyl [O(MeSiC4Ph4)2] (10) and methyl silicate.

Keywords

• silole anion
• silacyclopentadiene
• aromaticity
• dimer
• tricyclic diallylic dianion