Importance of Counterion Reactivity on the Deactivation of Co-Salen Catalysts in the Hydrolytic Kinetic Resolution of Epichlorohydrin

详细信息    查看全文

• 作者：Surbhi Jain ; Xiaolai Zheng ; Christopher W. Jones ; Marcus Weck ; Robert J. Davis
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：October 15, 2007
• 年：2007
• 卷：46
• 期：21
• 页码：8887 - 8896
• 全文大小：196K
• 年卷期：v.46,no.21(October 15, 2007)
• ISSN：1520-510X

文摘

Possible modes of deactivation of Jacobsen's Co-salen catalyst during the hydrolytic kinetic resolution (HKR) ofepichlorohydrin were explored by UV-vis spectroscopy, X-ray absorption spectroscopy, and electrospray ionizationmass spectrometry, combined with recycling studies. Although an active Co(III)-salen catalyst deactivated substantiallyafter multiple cycles without regeneration, the catalyst maintained its +3 oxidation state throughout the runs. Thus,deactivation of Co-salen during HKR was not the result of Co reduction. The mass spectrum of a deactivatedmaterial showed that catalyst dimerization does not account for the loss of activity. Results from various catalystpretreatment tests, as well as from catalysts containing various counterions (acetate, tosylate, chloride, iodide)indicated that the rate of addition of the Co-salen counterions to epoxide forming Co-OH during the reactioncorrelated with deactivation. The extent of counterion addition to epoxide was influenced by the exposure time andthe nucleophilicity of the counterion. An oligo(cyclooctene)-supported Co-OAc salen catalyst, which was 25 timesmore active than the standard Co-salen catalyst, was recycled multiple times with negligible deactivation.