An efficient, selective, and solventless approach to carbamates in DBU-derived ionic liquids: Experimental and theoretical investigations

Abstract

Herein, we report the synthesis of a diverse array of DBU (1,8-Diazabicyclo[5.4.0]undec-7-ene) based monocationic and dicationic ionic liquids with different inorganic and organic anions. All the synthesized ILs have been characterized by recording their 1H and 13C NMR spectra. The synthesized ILs have been utilized as catalysts in the carbamation of amines with dimethyl carbonate. A detailed study has been conducted to illuminate the possible mechanistic establishment by probing the role of catalysts played by the DBU and DBU-derived ionic liquids in the carbamation process. The attachment of the butyl group to the nitrogen of the DBU unit reversed the selectivity, which has been well established with the help of spectral techniques and theoretical (DFT) studies. The DBU-derived ionic liquids facilitated the N-methoxycarbonylation of amines over N-alkylation. Among all, the best carbamate yields were obtained in the presence of [BuDBU]Ala IL under optimized reaction conditions. The IL catalyst was efficiently reused five times without any significant catalytic loss. The current carbamation protocol possesses advantages like ease of setup, eco-friendly, catalytic reusability, and selectivity.