Cheng, Mu-Jeng and Bischof, Steven M. and Nielsen, Robert J. and Goddard, William A., III and Gunnoe, T. Brent and Periana, Roy A. (2012) The para-substituent effect and pH-dependence of the organometallic Baeyer–Villiger oxidation of rhenium–carbon bonds. Dalton Transactions, 41 (13). pp. 3758-3763. ISSN 1477-9226 http://resolver.caltech.edu/CaltechAUTHORS:20120410-080644226
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We studied the Baeyer–Villiger (BV) type oxidation of phenylrhenium trioxide (PTO) by H2O2 in the aqueous phase using Quantum Mechanics (density functional theory with the M06 functional) focusing on how the solution pH and the para-substituent affect the Gibbs free energy surfaces. For both PTO and MTO (methylrhenium trioxide) cases, we find that for pH > 1 the BV pathway having OH− as the leaving group is lower in energy than the one involving simultaneous protonation of hydroxide. We also find that during this organometallic BV oxidation, the migrating phenyl is a nucleophile so that substituting functional groups in the para-position of phenyl with increased electron-donating character lowers the migration barrier, just as in organic BV reactions. However, this substituent effect also pushes electron density to Re, impeding HOO− coordination and slowing down the reaction. This is in direct contrast to the organic analog, in which para-substitution has an insignificant influence on 1,2-addition of peracids. Due to the competition of the two opposing effects and the dependence of the resting state on pH and concentration, the reaction rate of the organometallic BV oxidation is surprisingly unaffected by para-substitution.
|Additional Information:||© 2012 The Royal Society of Chemistry. Received 19th October 2011, Accepted 21st December 2011. First published on the web 13 Feb 2012. This work was fully supported by the Center for Catalytic Hydrocarbon Functionalization, an Energy Frontier Research Center, DOE DE-SC0001298.|
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|Deposited By:||Tony Diaz|
|Deposited On:||10 Apr 2012 21:13|
|Last Modified:||26 Dec 2012 15:02|
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