Aerobic oxidation of benzylic alcohols with bis(3,5-di- tert-butylsalicylaldimine)copper(II) complexes

• Published in: Applied catalysis. A, General Vol. 371; no. 1; pp. 17 - 21
• Main Authors: Ahmad, Jahir Uddin, Figiel, Pawel J., Räisänen, Minna T., Leskelä, Markku, Repo, Timo
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.12.2009; Elsevier
• Subjects: Aerobic oxidation; Alcohols; Catalysis; Catalysts; Chemistry; Copper; Copper(II) complexes; Diffraction; Distortion; Exact sciences and technology; General and physical chemistry; Oxidation; Salicylaldimine; TEMPO; Terminals; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; TEMPO; Copper(II) complexes; Aerobic oxidation; Salicylaldimine; Alcohols; Copper II; Oxygen; Catalytic reaction; Crystals; Ions; Selectivity; Benzyl alcohol; Copper complex; Oxidant; Aldehyde; X ray diffraction; Geometry; Oxidation; Structure; Catalyst
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2009.09.011

A series of bis(3,5-di- tert-butylsalicylaldimine)copper(II) complexes were synthesized and employed in the catalytic oxidation of alcohols using molecular oxygen as a terminal oxidant. These complexes, when combined with TEMPO form a highly efficient catalytic system for the aerobic oxidation of primary benzylic and allylic alcohols under mild reaction conditions. For example at 60 °C and 1 bar of O 2 pressure benzyl alcohol is quantitatively converted to benzyl aldehyde in 2 h with low catalyst loading. Attractive features of this catalytic system include the efficient use of molecular oxygen, high selectivity, low loading of both TEMPO (2 mol%) and copper catalyst (0.66 mol%) and mild reaction conditions (atmospheric oxygen and 60 °C temperature). In addition, the crystal structure of the complex was determined by X-ray diffraction analysis. The structure presents the Cu ion in a monomeric distorted square-planar geometry involving the unusual and sterically unfavorable cis-N 2O 2 coordination sphere. A catalytic procedure for aerobic oxidation of alcohols was developed by utilizing bis(3,5-di- tert-butylsalicylaldimine)copper(II) complexes. The use of molecular oxygen as an ultimate stoichiometric oxidant, low loading of both TEMPO and copper catalyst make the system attractive candidate for sustainable oxidation of benzylic alcohols. Under optimal conditions, various alcohols could be selectively transformed into their corresponding aldehydes in excellent conversions.