Efficient and selective oxidation of tertiary benzylic CH bonds with O2 catalyzed by metalloporphyrins under mild and solvent-free conditions

• Published in: Applied catalysis. A, General Vol. 599; p. 1
• Main Authors: Shen, Hai-Min, Hu, Meng-Yun, Liu, Lei, Qi, Bei, Ye, Hong-Liang, She, Yuan-Bin
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05.06.2020; Elsevier Science SA
• Subjects: Alcohol; Alcohols; Autoxidation; Benzylic C[sbnd]H bond; Catalysts; Cumene; Manganese; Metalloporphyrin; Molecular oxygen; Oxidation; Planar structures; Reaction kinetics; Selectivity; Solvents; Substrates; Alcohol; Molecular oxygen; Oxidation; Metalloporphyrin; Benzylic CH bond
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2020.117599

Tertiary benzylic CH bonds were converted to corresponding alcohols directly and efficiently employing O2as oxidant and T(2,3,6-triCl)PPMn possessing bulkier substituents as catalyst under solvent-free and additive-free conditions, with higher conversion (57.6%) and selectivity (70.5%) than current documents under similar conditions. [Display omitted] •Direct conversion of tertiary benzylic CH bonds to alcohols was obtained mildly.•High performances of metalloporphyrins with bulky substituents were demonstrated.•Selectivity toward benzylic alcohols (70.5%) was higher than current documents.•A strategy for direct functionalization of tertiary benzylic CH bonds presented. The direct and efficient oxidation of tertiary benzylic CH bonds to alcohols with O2 was accomplished in the presence of metalloporphyrins as catalysts under solvent-free and additive-free conditions. Based on effective inhibition on the unselective autoxidation and deep oxidation, systematical investigation on the effects of porphyrin ligands and metal centers, and apparent kinetics study, the oxidation system employing porphyrin manganese(II) (T(2,3,6-triCl)PPMn) with bulkier substituents as catalyst, was regarded as the most promising and efficient one. For the typical substrate, the conversion of cumene could reach up to 57.6% with the selectivity of 70.5% toward alcohol, both of them being higher than the current documents under similar conditions. The superiority of T(2,3,6-triCl)PPMn was mainly attributed to its bulkier substituent groups preventing metalloporphyrins from oxidative degradation, its planar structure favoring the interaction between central metal with reactants, and the high efficiency of Mn(II) in the catalytic transformation of hydroperoxides to alcohols.