Sílica mesoporosa funcionalizada com grupos nitrogenados como suporte para a entrega e sequestro de espécies de cobre cataliticamente ativas na reação de acoplamento A3

Abstract

In this work, mesoporous silica MCM-41 was synthesized by using a template method and post-synthesisfunctionalized withAPTMS, using variouscoupling agent proportions. The functionalized groups were analyzed quantitatively by TGA and XPS and qualitatively by solidstated NMR for 29Si, which evidenced the anchoring of the organic chains onto the silicas surface, and for 13C, which evidenced the presence of aminopropil groups. The BET surface areas of the materials decreased with an increase in the degree of functionalization, hence the materialwith less anchored groups and highest surface area was used to immobilize Cu (I). The immobilized material efficiently catalyzed the A3-coupling reaction with 0.02 mol% of catalyst, the lowest load ever reported in the literature. The immobilized material was even more efficient than the homogeneous catalyst itself at the same conditions, pointing that the supports mesopores might have a fundamental role in the process, such as confining metallic species on their interiors and, therefore, creating nanoenvironments of higher catalyst load, improving the kinetic of the process as a whole. ICP-OES studies after the reaction completion showed total leaching of the copper which, although representing only 70 ppm of final product contamination (below the 300 ppm oral ingestion threshold stablished by FDA), can be in part scavenged by the support itself simply by stirring the system for extra 24h at room temperature. Thus, the support not only delivers catalytic active species to the system and scavenges part of them back at the end of the process, but also confine them inside of its pores and enables the use to an extremely low catalyst load, in the parts per million scale.