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- Title
A Density Functional Theory Investigation of the Cobalt-Mediated η<sup>5</sup>-Pentadienyl/Alkyne [5+2] Cycloaddition Reaction: Mechanistic Insight and Substituent Effects.
- Authors
Ylijoki, Kai E. O.; Budzelaar, Peter H. M.; Stryker, Jeffrey M.
- Abstract
Alkyl-substituted η5-pentadienyl half-sandwich complexes of cobalt have been reported to undergo [5+2] cycloaddition reactions with alkynes to provide η2,η3-cycloheptadienyl complexes under kinetic control. DFT studies have been used to elucidate the mechanism of the cyclization reaction as well as that of the subsequent isomerization to the final η5-cycloheptadienyl product. The initial cyclization is a stepwise process of olefin decoordination/alkyne capture, CC bond formation, olefin arm capture, and a second CC bond formation; the initial decoordination/capture step is rate-limiting. Once the η2,η3-cycloheptadienyl complex has been formed, isomerization to η5-cycloheptadienyl again involves several steps: olefin decoordination, β-hydride elimination, reinsertion, and olefin coordination; also here the initial decoordination step is rate limiting. Substituents strongly affect the ease of reaction. Pentadienyl substituents in the 1- and 5-positions assist pentadienyl opening and hence accelerate the reaction, while substituents at the 3-position have a strongly retarding effect on the same step. Substituents at the alkyne (2-butyne vs. ethyne) result in much faster isomerization due to easier olefin decoordination. Paths involving triplet states do not appear to be competitive.
- Publication
Chemistry - A European Journal, 2012, Vol 18, Issue 32, p9894
- ISSN
0947-6539
- Publication type
Article
- DOI
10.1002/chem.201200319