Heteroorganic betaines 5. A DFT study of the structure and reactivity of 6,6-dimethyl-6-sukafykvebe and silicon-containing organophosphorus betaine ~-C_5H_4SiMe_2CH_2PMe_3~+

摘要

The structures of 6,6-dimethyl-6-silafulvene C_5H_4SiMe_3 (3), its donor-acceptor complex with ammonia, C_5H_4SiMe_2 . NH_3, dimethylfulvene, a number of cyclopentadienylides, methylenetrimethylphosphorane (6), and silicon-containing organophosphorus betaine ~-C_5H_4SiMe_2CH_2PMe_3~+ (130, the product of nucleophilic addition of 6 to 3, were calculated using the density functional approach. For compound 13, the potential energy minimum corresponds to the conformation with gauche-arrangement of the cyclopentadienyl anionic and trimethylphosphonium cationic centers and a C-Si-C-P dihedral angle of 30.5 deg, which is rather stable toward decomposition into 3 and 6 (#DELTA#Hdeg = 42 kcal mol~(-1), #DELTA#G deg = 30 kcal mol~(-1)). The main hannel of thermal decomposition of compound 13 involves an intramoleuclar nucleophilic substitution, which proceeds with elimination of trimethylphosphine and resutls in 1,1-dimethyl-1-silaspiro[2,4]hepta-4,6-diene, which then undergoes a ready and irreversible isomerization into 6,6-dimethyl-6-siabicyclo[3.2.0]hepta-1,3-diene owing to the [1,5]-sigmatropic shift of the C-Si bond.