Metal-Free and Solvent-Free Oxidative Coupling of Amines to Imines with Mesoporous Carbon from Macrocyclic Compounds

Abstract

A new series of carbon-based heterogeneous catalysts aiming at the oxidative coupling of amines to imines is disclosed here, which are easily synthesized by pyrolysis of macrocyclic compounds, including phthalocyanine and porphyrin under different temperatures. Silica colloid or ordered mesoporous silica SBA-15 is employed as the hard template to fulfill the mesoporous structures. The most active catalyst fabricated from phthalocyanine and silica colloid shows remarkable catalytic activity, excellent selectivity, and robust stability toward the imine formation in the presence of molecular oxygen under neat conditions. Kinetic analysis demonstrates that the apparent activation for benzylamine oxidation is 47.6 kJ mol −1 and that cationic species are involved in the reaction. The unprecedented performance of mesoporous carbon catalysts can be attributed to their high surface area, profitable pore volume, as well as homogeneous distribution of defect sites.

POSS‐Based Nitrogen‐Doped Hierarchically Porous Carbon as Metal‐Free Oxidation Catalyst

“…The performance of these carbon materials in this oxidative coupling reaction is comparable to other metal‐free catalysts such as graphene‐oxide (GO), mpg‐C 3 N 4 , heteroatom‐doped porous carbons,, with the exception that longer reaction times are required to ensure full conversion. For example, Wang et al .…”

“…For example, Wang et al . recently reported a series of highly graphitized N‐doped carbons as metal‐free catalysts derived from MOFs , . When they were applied in the present reaction, similar results were found, with conversions up to >99 %, although, the nitrogen content of their catalysts was much higher (16.5 wt%).…”

Heteroatom‐Enhanced Metal‐Free Catalytic Performance of Carbocatalysts for Organic Transformations

“…Combining BNG with CNT can further enhance the catalytic efficiency as the generated multiple nanoscale carbon p–n junctions were beneficial to the activation of molecular oxygen . Subsequently, our group present that mesoporous carbons derived from phthalocyanine (Pc) and porphyrin also exhibit unprecedented performance for the self‐coupling of primary benzylic amines . Defect sites were established to be active sites.…”

Metal-free catalysis of nitrogen-doped nanocarbons for the ammoxidation of alcohols to nitriles

“…Up to 23 wt % concentration of nitrogen in DAA can achieve effectively own heteroatomdoping. Unlike macrocyclic compounds phthalocyanine and porphyrin 14 we previously used, DAA is promising nitrogen and carbon precursor and is easily synthesised. Its excellent solubility facilitates DAA to have sufficient contact with SiO2 nanosphere, further resulting in the high surface area (up to 906 m 2 /g).…”