Magnetic Nickel Nanoparticles Supported on Oxidized Charcoal as a Recoverable Catalyst for N-Alkylation of Amines with Alcohols

Abstract

Herein, we present a hassle-free approach to synthesize Ni nanoparticles (NPs) and support them onto oxidized charcoal (OC) to produce Ni-oxidized charcoal nanomaterials (Ni-OC). Subsequently, Ni-NPs and Ni-OCs are characterized using powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron (XPS) spectroscopy, transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) techniques. The size distribution curve reveals that the diameter of the Ni-NPs embedded in OC falls in the range of 3–7 nm. Surface area studies show that Ni-NPs and Ni-OC have specific surface areas of 36.5 and 248.9 m2/g, respectively. Interestingly, Ni-OC exhibits the soft ferromagnetic nature of nickel. Ni-NPs and Ni-OC are used as catalysts for the N-alkylation reaction between aniline and benzyl alcohol. The Ni-OC nanomaterials show excellent yields (70–92%) of N-alkylated products. Notably, a catalyst loading of only 0.0482 mmol is sufficient to activate a broad substrate scope with a large functional group tolerance. In addition, the developed synthetic protocol can be further exploited for the catalytic synthesis of 1,2-disubstituted benzimidazole derivatives in excellent yields (65–89%) and effective functional group tolerance. It has been observed that the hydrogen-borrowing mechanism powers both catalytic processes. The Ni-OC exhibits outstanding catalytic reusability and magnetic recoverability for the N-alkylation reaction of aniline with benzyl alcohol for more than seven reaction cycles. In contrast to Ni-NPs, the Ni-OC catalyst exhibits higher catalytic activity for the N-alkylation reaction. This could be explained by the interactions between Ni-NPs and the functional groups available on the oxidized charcoal, which enhance the surface area of the Ni-OC.