Solvent/metal-free benzimidazolium-based carboxyl-functionalized porphyrin photocatalysts for the room-temperature alkylation of amines under the irradiation of visible light

Abstract

The improvement of novel sustainable catalytic methods for green chemical production is an emergent area in chemical science. Herein, for the first time, a sustainable catalytic process was developed for the direct N-alkylation of primary and secondary amines with alcohols using efficient metal-free benzimidazolium-based carboxyl-functionalized porphyrin (MFBBCFPc) heterogeneous photocatalysts in a home-made photocatalytic reactor in the presence of LED light. In this context, the current protocol demonstrated metal-free conditions tolerating extensive substrate scope comprising primary amines, phenylenediamine, and secondary amines such as pyrrole, morpholine, and various alcohols, with water being the only by-product. The metal-free protocol was further supported by the ICP-OES data, indicating the negligible quantity of Pd/Ru in the photocatalyst and the product. The photocatalytic competence was studied under ambient conditions using 5 W LED light with high stability and substantial reusability for six runs without significant loss in the yield of alkylated products. The formation of alkylated amines proceeded via (i) the formation of aldehydes from the oxidation of alcohols on the surface of MFBBCFPc photocatalysts and (ii) the condensation of the amine with the aldehyde on the photocatalyst surface, followed by the hydrogenation of the obtained imine by hydrogen atoms on the surface of MFBBCFPc.