Abstract
The reaction of tricarbonyl(tropone)iron with tetracyanoethylene (TCNE) was reinvestigated. Two primary cycloadducts, the 3 + 2 and 4 + 2 isomers are formed in a 96/4 ratio. The second order rate constant for the reaction is k 4.4 × 10-2 M-1 s-1 (at 24°C, in acetone) with a free activation energy of ΔG# 19.2 kcal mol-1 The 3 + 2 cycloadduct undergoes a facile sigmahaptotropic rearrangement to the formal 5 + 2 adduct with rate constants of k 3.8 × 10-10 s-1 (24°C, acetone) and k 5.1 × 10-4 s-1 (24°C, methanol), and with activation parameters ΔH# 20 kcal mol-1 and ΔS# -7 e.u. (acetone). The kinetic results suggest that both the cycloaddition and the rearrangment are concerted, nonsynchronous, one-step reactions, involving a slightly polar transition state. Frontier molecular orbital considerations imply that the 3 + 2 and 4 + 2 cycloadditions are symmetry allowed reactions. The structural reorganization which takes place in the [3,3]-sigmahaptotropic rearrangement suggests that the metal migration proceeds by way of a Berry pseudorotation, and the simultaneous 1,3-sigmatropic shift occurs with configuration retention at the migrating carbon. A detailed molecular orbital analysis of the rearrangement is given.
Original language | English |
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Pages (from-to) | 219-233 |
Number of pages | 15 |
Journal | Journal of Organometallic Chemistry |
Volume | 294 |
Issue number | 2 |
DOIs | |
State | Published - 15 Oct 1985 |
Bibliographical note
Funding Information:We thank Mrs. Sima Alfi for her assistance in the experimental work. Support by the planning and Grant Committee of the Council for Higher Education for the purchase of the Bruker AM300 NMR Spectrometer is gratefully acknowledged.
Funding
We thank Mrs. Sima Alfi for her assistance in the experimental work. Support by the planning and Grant Committee of the Council for Higher Education for the purchase of the Bruker AM300 NMR Spectrometer is gratefully acknowledged.
Funders | Funder number |
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Council for Higher Education |