Electronic effects in (salen)Mn-based epoxidation catalysts |
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Authors: | Cavallo Luigi Jacobsen Heiko |
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Affiliation: | Department of Chemistry, Università di Salerno, Via Salvador Allende, Baronissi (SA) I-84081, Italy. |
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Abstract: | Presented are density functional calculations on various Mn(salen) systems that are active catalysts in the epoxidation of olefins. Correlation of various structural properties such as Mn=O bond strengths, atomic charges, and C-O distances of evolving bonds in transition state geometries with modified Hammett constants reveal a mechanistic picture of the epoxidation reaction, supporting previous experimental results. Enantioselectivity is tied to the position of a transition state along the reaction coordinate for the first C-O bond formation step, when an olefin is approaching the epoxidation catalyst. Electronic effects exhibited by the 5,5' substituents of the salen ligand manifest themselves in a tuning of the Mn=O bond strength, which in turn influences the C-O distance of the forming bond in the transition state geometry. |
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