Unusual Behavior of a Novel Heterogeneous Chiral Dimer Cr(III)鈭扴alen Complex in the Epoxidation/Epoxide Ring-Opening Reaction of trans-Methylcinnamate Ester

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• 作者：Loredana Protesescu ; Madalina Tudorache ; Stefan Neatu ; Maria Nicoleta Grecu ; Erhard Kemnitz ; Petru Filip ; Vasile I. Parvulescu ; Simona M. Coman
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：February 3, 2011
• 年：2011
• 卷：115
• 期：4
• 页码：1112-1122
• 全文大小：401K
• 年卷期：v.115,no.4(February 3, 2011)
• ISSN：1932-7455

文摘

A dimer chromium(III)鈭抯alen complex immobilized on modified silica is an effective catalyst for the epoxidation/epoxide ring-opening reaction of trans-methylcinnamate ester and gave significantly high ee in methyl (2R,3S)-2,3-dihydroxy-3-phenylpropionate. For the first time, it is shown that a donor ligand (e.g., Et₃N) can be involved into the enantioselective mechanism of the product configuration. It is suggested that the additive is interacting with the reaction intermediate in a manner that prolongs its lifetime, thus affording a free rotation of the C鈭扖 single bond in this species and a selective collapse to the cis-epoxide product. In the presence of water, this epoxide led to methyl (2S,3R)-2,3-dihydroxy-3-phenylpropionate. Alternatively, the donor additives may give rise to a new chromium-based oxidant that effects epoxidation and its consecutive ring opening to diols via an unusual pathway.