Amino-grafted mesoporous materials based on MCF structure involved in the quinoline synthesis. Mechanistic insights

• Amino-grafted NbMCF materials are useful catalysts for the Friedländer reaction.
• Non-activated samples were more efficient catalysts than the activated ones.
• Water is probably involved on the stabilization of intermediate species.
• Higher nitrogen content in MCF is probably responsible of the observed reactivity.

We report here a new series of ordered mesoporous metallosilicates which have been found to be efficient heterogeneous catalysts for the Friedländer condensation. 3-Aminopropyl-trimethoxysilane (APMS) and [3-(2-aminoethylamino)propyl] trimethoxysilane (2APMS) have been supported by grafting on a Mesoporous Cellular Foam (MCF). For comparison, both APMS and 2APMS have also been supported on an Nb-containing Mesoporous Cellular Foam (NbMCF). These hybrid materials have been tested in the reaction between 2-amino-5-chlorobenzaldehyde and ethyl acetoacetate leading to ethyl 6-chloro-2-methylquinoline-3-carboxylate with total selectivity. The condensation was more efficient when using 2APMS/MCF sample which exhibits higher nitrogen content than APMS/MCF. However, this trend was inverted when using the niobiosilicates analogues, most likely as a consequence of the interaction of amine groups with the niobium atoms in the siliceous framework. Experimental and theoretical studies demonstrated that the presence of water in non-activated samples plays an important role in the formation of the corresponding quinoline by stabilizing key transition structures and intermediate species.

MCF materials were found to be efficient catalysts for the synthesis of quinolines from 2-amino-5-chlorobenzaldehyde (7) and ethyl acetoacetate (2). Based on our experimental observations we theoretically demonstrated that traces of water presents in catalysts plays a critical role on the annulations reaction.Figure optionsDownload high-quality image (106 K)Download as PowerPoint slide