Eco-friendly functionalization of natural halloysite clay nanotube with ionic liquids by microwave irradiation for Suzuki coupling reaction

Abstract

Microwave assisted halloysite (HNT) external surface functionalization with ionic liquids is described. HNTs modification was achieved in two steps: a) grafting of 3-mercaptopropyl trimethoxysilane on the external surface of HNT by a microwave irradiation; b) anchorage of vinylimidazolium ionic liquids by a thiol-ene reaction. MW irradiation allowed us to obtain high loading onto the HNT surface compared to those obtained through conventional synthesis. Fourier transform infrared spectroscopy and thermogravimetric analysis confirmed that the grafting has occurred only on the external surface of HNT. Turbidimetric and dynamic light scattering analyses showed that the introduction of ionic liquid on the HNT surface involves the formation of aggregates. One of these materials has been used as support for Palladium particles and tested, as catalyst, in the Suzuki reaction between phenylboronic acid and some aryl halide to give the corresponding biaryl in high yield. A catalytic efficiency higher than conventionally used support was achieved.