Heteroorganic betaines |
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Authors: | M S Nechaev I V Borisova N N Zemlyanskii D N Laikov Yu A Ustynyuk |
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Institution: | (1) Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory, 119899 Moscow, Russian Federation;(2) State Research Center of the Russian Federation “State Research Institute of Chemistry and Technology of Organoelement Compounds”, 38 sh. Entuziastov, 111123 Moscow, Russian Federation |
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Abstract: | The structures of 6,6-dimethyl-6-silafulvene C5H4SiMe2 (3), its donor-acceptor complex with ammonia. C5H4SiMe2·NH3, dimethylfulvene, a number of cyclopentadienylides, methylenetrimethylphosphorane (6), and silicon-containing organophosphorus betaine−C5H4SiMe2CH2PMe3
+ (13), the product of nucleophilic addition of6 to3, were calculated using the density functional approach. For compound13, the potential energy minimum corresponds to the conformation withgauche-arrangement of the cyclopentadienyl anionie and trimethylphosphonium cationic centers and a C−Si−C−P dihedral angle of 30.5°,
which is due to the Coulomb attraction between these centers. According to calculations, betaine13 is rather stable toward decomposition into3 and6 (ΔH
o=42 kcal mol−1, ΔG
Δ=30 kcal mol−1). The main channel of thermal decomposition of compound13 involves an intramolecular nucleophilic substitution, which proceeds with elimination of trimethylphosphine and results in
1,1-dimethyl-1-silaspiro2,4]hepta-4,6-diene, which then undergoes a ready and irreversible isomerization into 6,6-dimethyl-6-silabicyclo3.2.0]hepta-1,3-diene
owing to the 1.5]-sigmatropic shift of the C−Si bond.
For Part 4, see Ref. 1.
Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1850–1857, November, 2000. |
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Keywords: | silaolefins silafulvene silicon-containing organophosphorus betaines nonempirical quantum-chemical calculations density functional theory |
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