Efficient and selective aerobic oxidation of alcohols into aldehydes and ketones using ruthenium/TEMPO as the catalytic system. |
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| Authors: | A Dijksman A Marino-González A Mairata I Payeras I W Arends R A Sheldon |
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| Institution: | Laboratory for Organic Chemistry and Catalysis, Department of Biotechnology, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands. |
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| Abstract: | The combination of RuCl2(PPh3)3 and TEMPO affords an efficient catalytic system for the aerobic oxidation of a variety of primary and secondary alcohols, giving the corresponding aldehydes and ketones, in >99% selectivity in all cases. The Ru/TEMPO system displayed a preference for primary vs secondary alcohols. Results from Hammett correlation studies (rho = -0.58) and the primary kinetic isotope effect (kH/kD = 5.1) for the catalytic aerobic benzyl alcohol oxidations are inconsistent with either an oxoruthenium (O=Ru) or an oxoammonium based mechanism. We postulate a hydridometal mechanism, involving a "RuH2(PPh3)3" species as the active catalyst. TEMPO acts as a hydrogen transfer mediator and is either regenerated by oxygen, under catalytic aerobic conditions, or converted to TEMPH under stoichiometric anaerobic conditions. |
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