Mechanism of Ethene Trimerization at an a nsa-(Arene)(cyclopentadienyl) Titanium Fragment

A theoretical study of ethene trimerization at a cationic (C6H5CH2C5H4)Ti fragment generally supports the metallacycle mechanism proposed earlier for this reaction. However, the crucial formation of the 1-hexene complex from a titanacycloheptane intermediate occurs by direct Cβ → Cα ‘ hydrogen trans...

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Bibliographic Details
Published in:Organometallics 2003-06, Vol.22 (13), p.2564-2570
Main Authors: Blok, Arno N. J, Budzelaar, Peter H. M, Gal, Anton W
Format: Article
Language:English
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Summary:A theoretical study of ethene trimerization at a cationic (C6H5CH2C5H4)Ti fragment generally supports the metallacycle mechanism proposed earlier for this reaction. However, the crucial formation of the 1-hexene complex from a titanacycloheptane intermediate occurs by direct Cβ → Cα ‘ hydrogen transfer rather than by the more traditional β-elimination/reductive elimination sequence. The pendant arene moiety “breathes” during the reaction, being more strongly bound at the TiII stage than at the TiIV stage of the reaction. Its main role is to make the olefin complex formation more endothermic, thus increasing the barriers for formation of titanacyclopentane and titanacycloheptane intermediates. For the “naked” (C5H5)Ti system, which lacks this effect, further ring growth wins over hexene formation. But even for the bridged (C6H5CH2C5H4)Ti system, we find that the various reactions are very delicately balanced.
ISSN:0276-7333
1520-6041
DOI:10.1021/om030049o