Osmium(ii) complexes for light-driven aerobic oxidation of amines to imines

Abstract

Herein, we describe the synthesis and characterization of three Os(ii) complexes (i.e., [Os(fptz)2(PPhMe2)2] (1, fptzH = 3-trifluoromethyl-5-pyridyl-1,2,4-triazole), [Os(fptz)2(CO)(L1)] (2, L1 = PPh3; 3, L1 = pyridine)) that have been successfully utilized as good photocatalysts to promote aerobic oxidative coupling of amines to imines with molecular oxygen in air as a green oxidant. Complex 1 is the most effective catalyst for the oxidative coupling of benzylamine with molecular O2 (air) as the oxidant because of the complex's strong absorption of visible light and long-lived triplet state. The application of a low catalyst loading (0.06 mol%) of complex 1 to the oxidative coupling of a wide range of amines affords the corresponding imines efficiently and selectively in most cases. The reaction mechanism was investigated via relevant control and quenching experiments. The results indicated that the reaction occurs via an active (1)O2-involved pathway. The (1)O2-generating ability of complex 1 as a photosensitizer was evaluated using 9,10-dimethylanthracene (DMA) as a chemical trap for (1)O2.

Carbon nitride creates thioamides in high yields by the photocatalytic Kindler reaction

“…In recent years, usage of visible light energy as a driving force for organic synthesis has gained significant attention. 1,2 A large body of studies has been published, where different organic dyes [3][4][5][6] or metal complexes [7][8][9] are used as photocatalysts. These catalysts have already proven to be very efficient for a broad range of photocatalytic reactions.…”

A Porphyrin‐Based Covalent Organic Framework for Metal‐Free Photocatalytic Aerobic Oxidative Coupling of Amines

“…At present, many catalytic materials, such as noble metals, non‐noble metals [10] and photocatalysts [11] have been reported for the reaction of the oxidation coupling of primary amine to imine. Noble metals such as gold, [12] platinum [13] and osmium, [14] have been widely used to catalyze the reaction, which show good catalytic performance. But the high cost limits their potential for large‐scale application [15] .…”

Azolate‐Based Osmium(II) Complexes with Luminescence Spanning Visible and Near Infrared Region

“…Structure of complexes 52-57. 24 hours. This manipulation gave isolation of a dinuclear complex [Os 2 (CO) 4 (fpbpy) 2 ] (58) as air-stable, red crystalline solids.…”

“…Alternatively, osmium(II) complexes relevant to 15 and 23 have been tested as potential photocatalysts for formation of imines from oxidative coupling of amines with air as a green oxidant [24] . Red emissive complex 23 showed strong absorption at the longer wavelength region and long‐lived triplet excited state in comparison to that of 15 and, hence, it represents the most effective catalyst for such oxidative coupling of amine in giving formation of imine.…”