Mechanism of Titanocene-Mediated Epoxide Opening through Homolytic Substitution
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- 作者：Andreas Gansä ; uer ; Andriy Barchuk ; Florian Keller ; Martin Schmitt ; Stefan Grimme ; Mareike Gerenkamp ; Christian Mü ; ck-Lichtenfeld ; Kim Daasbjerg ; Heidi Svith
- 刊名：Journal of the American Chemical Society
- 出版年：2007
- 出版时间：February 7, 2007
- 年：2007
- 卷：129
- 期：5
- 页码：1359 - 1371
- 全文大小：498K
- 年卷期：v.129,no.5(February 7, 2007)
- ISSN：1520-5126
文摘
The mechanism of titanocene-mediated epoxide opening was studied by a combination ofvoltammetric, kinetic, computational, and synthetic methods. With the aid of electrochemical investigationsthe nature of a number of Ti(III) complexes in solution was established. In particular, the distribution ofmonomeric and dimeric Ti(III) species was found to be strongly affected by the exact steric conditions. Theoverall rate constants of the reductive epoxide opening were determined for the first time. These datawere employed as the basis for computational studies of the structure and energies of the epoxide-titanocene complexes, the transition states of epoxide opening, and the 
-titanoxy radicals formed. Theresults obtained provide a structural basis for the understanding of the factors determining the regioselectivityof ring opening and match the experimentally determined values. By employing substituted titanoceneseven more selective epoxide openings could be realized. Moreover, by properly adjusting the steric demandsof the catalysts and the substrates the first examples of reversible epoxide openings were designed.
-titanoxy radicals formed. Theresults obtained provide a structural basis for the understanding of the factors determining the regioselectivityof ring opening and match the experimentally determined values. By employing substituted titanoceneseven more selective epoxide openings could be realized. Moreover, by properly adjusting the steric demandsof the catalysts and the substrates the first examples of reversible epoxide openings were designed.