Modified Active Site Coordination in a Clinical Mutant of Sulfite Oxidase

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• 作者：Christian J. Doonan ; Heather L. Wilson ; K. V. Rajagopalan ; Robert M. Garrett ; Brian Bennett ; Roger C. Prince ; Graham N. George
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：May 14, 2008
• 年：2008
• 卷：130
• 期：19
• 页码：6298 - 6298
• 全文大小：49K
• 年卷期：v.130,no.19(May 14, 2008)
• ISSN：1520-5126

文摘

The surface complex [(acs.org/images/entities/tbd1.gif">SiO)Re(acs.org/images/entities/tbd1.gif">CtBu)(acs.org/images/entities/dbd_2.gif">CHtBu)(CH₂tBu)] (1) is a highly efficient propene metathesis catalyst with high initial activities and a good productivity. However, it undergoes a fast deactivation process with time on stream, which is first order in active sites and ethene. Noteworthy, 1-butene and pentenes, unexpected products in the metathesis of propene, are formed as primary products, in large amount relative to Re (>>1 equiv/Re), showing that their formation is not associated with the formation of inactive species. DFT calculations on molecular model systems show that byproduct formation and deactivation start by a β-H transfer trans to the weak σ-donor ligand (siloxy) at the metallacyclobutane intermediate having a square-based pyramid geometry. This key step has an energy barrier slightly higher than that calculated for olefin metathesis. After β-H transfer, the most accessible pathway is the insertion of ethene in the Re−H bond. The resulting pentacoordinated trisperhydrocarbyl complex rearranges via either (1) α-H abstraction yielding the unexpected 1-butene byproduct and the regeneration of the catalyst or (2) β-H abstraction leading to degrafting. These deactivation and byproduct formation pathways are in full agreement with the experimental data.