I. Gridnev, O. Tok, N. A. Gridneva
Jan 23, 1998
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0
Influential Citations
17
Citations
Journal
Journal of the American Chemical Society
Abstract
The synthesis of cycloheptatrienyl(dipropyl)borane (2a) was accomplished via the exchange reaction of trimethyl(cycloheptatrienyl)tin (6) and dipropylchloroborane. Compound 2a was found by NMR spectroscopy to equilibrate with its valence tautomer 7-exo-(dipropylboryl)norcaradiene (2b). The equilibrium between 2a and 2b was studied in detail experimentally by variable temperature NMR and theoretically by ab initio calculations of size-reduced molecular systems (2a and 2b, with methyl instead of n-propyl groups) at the B3LYP/6-311+G*//B3LYP/6-31G* + ZPVE level. Experimentally determined thermodynamic parameters of the equilibrium (ΔH = 2.4 ± 0.1 kcal mol-1; ΔS = −5.5 ± 0.3 cal mol-1 K-1) and the activation barriers at 228 K (ΔG⧧228(2a→2b) = 8.2 ± 0.1 kcal mol-1, ΔG⧧228(2b→2a) = 9.4 ± 0.1 kcal mol-1) are in reasonable agreement with the computed results (ΔH = 2.0 kcal mol-1, ΔS = −3.7 cal mol-1 K-1; ΔG⧧228(2a→2b) = 3.2 kcal mol-1 and ΔG⧧228(2b→2a) = 6.7 kcal mol-1). The computations also indicate that 7-endo...