Title: Polyethylenimine-based materials: Novel heterogeneous catalysts for sustainable organic transformations

Abstract

Polyethyleneimine (PEI), thanks to the presence of nitrogen atoms, is known to be a suitable material for catalysis. In most cases, PEI is used as a grafting agent or as a support for catalytically active metal species whereas only few cases report its use in amine-catalyzed organic transformations. In our team, we developed a new class of cellulose-PEI-based materials obtained by the combination of TEMPO-oxidized cellulose nanofibers (TOCNF) with branched polyethyleneimine (bPEI) and citric acid (CA). The result is a nano-porous material with the characteristics of a Cellulose-based Nano-Sponge (CNS) to be used as catalyst for organic reactions. In this contest, the preparation of heterogenous catalysts from biomass sources is of great interest: beside the use of cellulose from renewable sources, the possibility to employ raw materials and waste as a source has been also explored, thus moving forward to reducing environmental impacts of organic transformations. Herein we report on the use of PEI based CNSs as heterogenous catalyst for organic reactions, with particular attention to the synthesis of precursors of interest for the pharmaceutical industry. In a first work, the CNSs have been used as basic amine catalyst for the Henry and Knoevenagel reactions, affording the products in good yields and selectivity. Then, exploiting the coordinating capability of PEI, the material has been loaded with metals, namely copper, zinc and palladium. These new catalysts proved to be very effective in metal catalyzed organic reactions as acetal formation and Suzuki-Miyaura coupling between aryl halides and phenyl boronic acid in water.