Synthesis and Improving the Crystallinity of a Squaranine Covalent Organic Framework by Investigating the Co-Catalyst Effect and Using It as a green and Metal-Free Catalyst for the synthesis of enaminones

Abstract

Herein, a modified synthesis method was presented and the effect of using an aqueous acetic acid solution in the process of synthesizing SQCOF was investigated. The addition of a catalytic amount of aqueous acetic acid solution as a co-catalyst has contributed to improved crystallinity quality. Effective parameters of the acid catalyst and the solvent were optimized and the synthesized SQCOF was used as a metal-free catalyst with Bronsted acid groups in the condensation reaction between 1,3-dicarbonyl groups and primary amines. This COF performs excellently as an acidic catalyst with a highly crystalline structure. SQCOF was applied in solvent-free conditions to synthesize enaminones at ambient temperature by gentle manual grinding with a pestle and mortar. High performance and efficiency (62 to 96 %), high TOF (833 to 1283 h-1), short reaction time, easy workup, elimination of toxic organic solvents, removal of metaled catalysts, and green conditions are the main advantages of this study. SQCOF shows good chemical stability and recyclability (7 runs) and acted as a successful catalyst in the synthesis of enaminones.