Efficient and Selective Aerobic Oxidation of Alcohols into Aldehydes and Ketones Using Ruthenium/TEMPO as the Catalytic System

• Published in: Journal of the American Chemical Society 2001-07, Vol.123 (28), p.6826-6833
• Main Authors: Dijksman, Arné, Marino-González, Arturo, Mairata i Payeras, Antoni, Arends, Isabel W. C. E, Sheldon, Roger A
• Format: Article
• Language: English
• Subjects: Aerobiosis; Alcohols - chemistry; Alcohols - metabolism; Aldehydes - chemistry; Aldehydes - metabolism; Catalysis; Cyclic N-Oxides - chemistry; Cyclic N-Oxides - metabolism; Ketones - chemistry; Ketones - metabolism; Oxidation-Reduction; Ruthenium - chemistry; Ruthenium - metabolism; Spin Labels
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0103804

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 (ρ = −0.58) and the primary kinetic isotope effect (k H/k D = 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.