Visible‐Light‐Driven Selective Oxidative Coupling of Amines to Imines by Bismuth‐Rich Bismuth Oxybromide in Water

Abstract

Photocatalytic selective oxidative coupling of amines is a promisingm ethod for imine synthesis. Bismuth-rich bismuth oxybromide photocatalysts have been found to exhibit improvedc onversion and selectivity for the visible-light-driven selectiveo xidative coupling of amines to imines in water.B enzylaminesw ith either electron-withdrawing or electron-donating groups undergo good conversion (94-99 %) and excellent selectivity (93-98 %) to the corresponding imines. The average apparent quantum efficiency at 455 nm is 57.4 %. Active species trapping experiments, isotope experiments, and in situ infrared spectroscopy reveal that water both serves as solvent and participates in the coupling reactiona sareactant. This work provides ag reen and environmentally friendly method for the efficient synthesis of imines with bismuth-richb ismuth oxyhalides and reveals water is involved in the oxidative coupling mechanismo fbenzylamines.Imines are an active intermediate in organic synthesis and can participate in reactions such as reductions, additions, condensations, and cycloadditions. [1] In addition, imine compounds show good antibacterial activities and have applicationsi n medicine and biology,o wing to their excellent pharmacological and biological activities. [2] Therefore, there is increased interest in the synthesis of imines by the hydrogenationo fn itro compounds, [3,4] oxidation and condensation of amines and alcohols, [5,6] and oxidative dehydrogenation of secondary amines. [7] However,t he above synthetic strategies are very difficult on an industrial scale because of the need for expensive reagentso rt oxic materials, and produce stoichiometric byproducts.T he oxidative coupling of amines to imines is an efficient route due to the high atomice conomy and environmentally friendly nature.This reactionist raditionally catalyzed thermally rather than photochemically,w hich is am ild, clean effi-cient method in organic synthesis. [8,9] Therefore, the photocatalytic oxidative coupling of amines was investigated asa promising methodf or imine synthesis.Optimized catalysts, solvents, andl ight sources are very important to achieveh igh selectivity and conversion in photocatalytic reactions. Currently,t he photocatalytic oxidative conversion of amines to imines has been investigated with several semiconductor systems, such as TiO 2 , [10][11][12][13][14] g-C 3 N 4 , [15][16][17] Nb 2 O 5 , [18,19] CdS, [20] ZnIn 2 S 4 , [21] MoS 2 , [22] and metal-organic frameworks MOFs). [23] However,t here are many shortcomings with these photocatalysts,s uch as UV excitation forT iO 2 and Nb 2 O 5 ,ahigh pressure of O 2 or high reaction temperatures requiredf or good conversion with g-C 3 N 4 and MoS 2 ,a nd the low photocatalytic stabilityo fC dS and ZnIn 2 S 4 .M ore importantly, the above systems typically require organic solvents, such as acetonitrile, benzene, or dichloromethane. Environmentally friendly approaches, according to the tenets of green chemistry,s hould limit the use of such organic solvents. Therefore, our approac...

Tuneable Phase, Morphology, and Performance of Bismuth Oxyhalide Photocatalysts via Microwave-Assisted Synthesis

“…The oxidative coupling of benzylamine to N -benzylidenebenzylamine (Scheme ) was chosen as a representative reaction to compare the photocatalytic abilities of the materials (Figure a,b and Table S14). Sustainable synthesis of imines is of industrial importance due to the prevalence of imines as precursors to pharmaceuticals and biologically active compounds, and the band structures of the bismuth oxyhalides are compatible with the redox potentials of the benzylamine oxidation reaction. , Several proposed mechanistic pathways exist for the photocatalytic oxidation of benzylamine, proceeding via the formation of superoxide and benzylammonium cation radicals . In this study, the aim was not to optimize conversion or maximum quantum efficiency for each material, but rather to evaluate the trends in performance with changes in phase, crystallinity, or morphology.…”

Synergistic Pd Single Atoms, Clusters, and Oxygen Vacancies on TiO2 for Photocatalytic Hydrogen Evolution Coupled with Selective Organic Oxidation

“…Upon irradiation, these peak intensities gradually decrease with the extension of irradiation time, suggesting that the photocatalytic reaction takes place. [ 45 ] Furthermore, the band around 1658 cm −1 increases with the prolonged irradiation time, due to the formation of CN in the PhHCNH intermediate or the final product of N‐benzylidenebenzylamine. [ 46 ]…”

Innovative green oxidation of amines to imines under atmospheric oxygen

“…Therefore, bismuth oxyhalides (BiOX, X = Cl, Br, I) and bismuth vanadium oxide (BiVO 4 ) are found to be efficient photocatalysts under visible light irradiation for the selective oxidation of amines, especially secondary amines to the corresponding imines with high activity and selectivity using oxygen as an oxidant (Scheme 19). 50…”