Aerobic Oxidation of Amines to Imines by Cesium-Promoted Mesoporous Manganese Oxide

Abstract

Selective oxidation of amines to imines is one of the most studied reactions in the field of heterogeneous catalysis. Cs ion promoted mesoporous manganese oxide (meso Cs/MnO x ) was synthesized using inverse surfactant micelle as a soft template. The chemical and structural properties of the mesoporous manganese oxide material were characterized by powder X-ray diffraction (PXRD), nitrogen sorption, electron microscopy and X-ray photoelectron spectra (XPS). The meso-Cs/MnO x material presented aggregated nanocrystalline nature with monomodal mesoporous size distributions. The catalyst was found to be effective in oxidation of amines to imines under aerobic conditions. The meso Cs/MnO x exhibited oxidation of primary, secondary, cyclic, aromatic, and aliphatic amines to imines, where the conversions reached as high as >99%. The catalyst was also effective in oxidative cross condensation of two different amines to produce asymmetrically substituted imines. Surface active Mn 3+ species along with labile lattice oxygen were found to play an important role in the catalytic activity. Mild reaction conditions (air atmosphere and absence of any oxidative or basic promoters), ease of product separation by simple filtration and significant reusability make this mesoporous manganese oxide material an economical and ecofriendly catalyst for the syntheses of versatile imine derivatives.

Aerobic Oxidation of Primary Amines to Imines in Water using a Cobalt Complex as Recyclable Catalyst under Mild Conditions

“…On the basis of above experiments and supported by previous literature, [7][8][9][10] ap lausible reaction mechanism for the oxidative coupling of benzylamine with the catalysthas been proposed as shown in Scheme5. Compound A,[ Co II (bpb)] reacts with oxygen to generate the active intermediate B,w hich coordinates with benzylamine to form the intermediate D. [7,9] Intermediate D can also be generated via intermediate C'.I ti ss ubsequently converted to a Schiff base intermediate E and H 2 O. [7a, 9] We would also like to mention that formation of as uperoxo intermediate that abstractsahydrogen atom from the amine to form an imine could not be rule out.…”

“…[6a] Therefore, bioinspiredc atalysts using benzoquinonec ofactor have received particulara ttentiona nd attempts have been made to mimic these catalytic systemsu sing metal-based catalysts and organocatalysts( Scheme 1). [7][8][9] Metalloporphyrins, ast he model of cytochrome P-450, have been used recently as bioinspired catalysts for amine oxidation. [6a] These include the use of ambient air ratherthan pure molecular oxygen as oxidant, reactions carried out at room temperature, high turnover number (TON), high selectivity,c atalystr ecyclability,u se of biocompatible catalysts rathert han preciousm etals and most importantly,u se of pure water as the only solvent.…”

“…[6a] These include the use of ambient air ratherthan pure molecular oxygen as oxidant, reactions carried out at room temperature, high turnover number (TON), high selectivity,c atalystr ecyclability,u se of biocompatible catalysts rathert han preciousm etals and most importantly,u se of pure water as the only solvent. [8] Recent reports by Wei and co-workers on amineo xidation using non-precious metal catalysts supported by inorganicl igands have shown recyclability of the catalysts. [7][8][9] Metalloporphyrins, ast he model of cytochrome P-450, have been used recently as bioinspired catalysts for amine oxidation.…”

“…[7][8][9][10] Therefore, to find out the possibility of ar adicalp athway,w ec arriedo ut the reactions with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) free radicala nd butylated hydroxytoluene (BHT;S cheme 4, entry 5). [7][8][9][10] Therefore, to find out the possibility of ar adicalp athway,w ec arriedo ut the reactions with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) free radicala nd butylated hydroxytoluene (BHT;S cheme 4, entry 5).…”

Defective Tungsten Oxide Hydrate Nanosheets for Boosting Aerobic Coupling of Amines: Synergistic Catalysis by Oxygen Vacancies and Brønsted Acid Sites

“…The initial catalytic assessments are performed at 353 K using oxygen molecules as an oxidant. As a model substrate (illustrated in Figure a), 4‐methyl‐benzylamine ( 1A ) is first oxidized to 4‐methyl‐benzaldehyde ( 2A ) and eventually coupled into the corresponding imine ( 2B ) as a final product . We perform the catalytic performance evaluation using various catalysts, while no products are detected in the absence of catalysts (Table S2, Supporting Information, Entry 1).…”