Reactions of coordinated cyclic polyolefins. A kinetic study of the pericyclic [3,3]-sigmahaptotropic rearrangement

Zeev Goldschmidt, Hugo E. Gottlieb, Drora Cohen

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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 languageEnglish
Pages (from-to)219-233
Number of pages15
JournalJournal of Organometallic Chemistry
Issue number2
StatePublished - 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.


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