Ionic liquid-based periodic mesoporous organosilicas: Metal/solvent-free synthesis of formamides and formamidines

Abstract

We prepared a novel ionic liquid-based Periodic Mesoporous Organosilicas (PMOs) using a post-synthetic method. First, PMO containing amine unit (PMO-NH) was prepared as a result of the co-condensation of amine bis-silane precursor [bis[3-(triethoxysilyl)propyl]amine] and tetraethylorthosilicate (TEOS) in the presence of pluronic-123 under acidic conditions. In a second step, the amine units (NH) were reacted with perchloric acid and yielded ionic-PMO material (PMO-NH2+ClO4−). The materials possessed a hexagonal lattice with the highly ordered mesostructured being retained after the functionalization as evidenced by X-ray diffraction (XRD) analysis. The N2 adsorption-desorption measurement revealed that the final material (PMO-NH2+ClO4−) had a high BET surface area (350 m2/g) and pore size (4.8 nm). The obtained material was subsequently evaluated as a heterogeneous catalyst in the coupling reaction of amine/formic acid towards formamides and also in the preparation of formamidine derivatives. The reactions between various aryl amines and formic acid or triethyl orthoformate could proceed smoothly in the presence of PMO-NH2+ClO4−, giving a high yield of 85–99% with great selectivity (> 99%). This outstanding catalytic performance can be attributed to the presence of acidic ionic sites together with a high surface area of the obtained material.