ENCAT

Synthesis of new Schiff base derived catalysts: application towards enantioselective reactions in greener and more sustainable media

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 Obiettivo del progetto (Objective)

'Over the past few years, the need for greener processes in chemical industries has considerably grown up. In order to solve the issue of organic solvents, non-pollutants media such as water, fluorinated solvents and supercritical fluids (SCFs) have attracted increasing attention. Beside, the demand for enantiopure compounds in the life sciences has stimulated interest in asymmetric catalysis. So the use of asymmetric catalysts in green solvents holds much promise for the development of sustainable chemical manufacturing. Among numerous catalysts, Schiff base complexes of metal ions show high catalytic activity and are commonly used in various reactions but the employment of these catalysts in environmentally friendly solvents still rare particularly for asymmetric catalysis. Also we propose to develop new chiral Schiff base complexes, which can be used in supercritical fluids and perfluorinated solvents. We will focus on supercritical carbon dioxide (scCO2). One of the challenges of the proposal consists in obtaining soluble ligands in these media. The synthesis of ligands with hydrocarbon or fluorocarbon chains should solve this issue. Another concept that will be envisaged is the use of water-soluble catalysts in scCO2-water biphasic systems by addition of hydrophilic arms on the ligands. The ligands will be synthesized in few steps by condensation of primary amines and aldehydes to match the demand of low-cost, environmentally friendly, and rapid synthesis. After complexation with metals, reactions such as oxidation, epoxidation and aldolisation will be studied as well as the recovery and reuse of the catalysts. Particularly, small cyclic ether molecules will be engaged in enantioselective reactions as models to develop useful methodologies in the synthesis of bioactive cyclic ethers. Finally, our objective is to bring efficient tools for the chemists worldwide to transfer the asymmetric catalysis methodology to large-scale synthesis technology.'

Introduzione (Teaser)

New catalytic compounds developed by researchers for use in industrially relevant chemical reactions without the need for volatile organic solvents hold great promise for using readily affordable substances in environmentally friendly media.

Descrizione progetto (Article)

Organic solvents have received vast criticism and their use has been restricted in many ways due to their association with the emission of hazardous volatile organic compounds (VOCs) into the air at normal room temperatures and pressures.

Together with greener solvents, the use of asymmetric catalysts has been gaining interest by the chemical industry in an effort to prepare pure enantiomer compounds, or compounds possessing only one of the two possible mirror image configurations of certain molecules.

Among potential catalysts, Schiff base complexes of metal ions demonstrate high catalytic activity but are generally insoluble in inorganic solvents.

Given that Schiff bases are important intermediates in a number of organic synthesis reactions including epoxidation, European researchers chose to develop new Schiff base type catalysts for use in environmentally friendly solvents with EU funding for the ENCAT project.

In order to develop new Schiff base complexes, researchers sought to create a new series of affordable ligands to be bound to non-toxic metals for use in epoxidation of terminal olefins in a green medium.

Three new organic ligands were prepared. From these, researchers synthesised manganese complexes and evaluated their catalytic activity in epoxidation of three olefins mediated either by hydrogen peroxide (H2O2) or iodosylbenzene (PHIO).

The new manganese complexes demonstrated very strong catalytic activity with the former and promising activity with the latter.

Physicochemical characterisations were performed leading to enhanced understanding of the mechanisms and structural factors controlling catalytic activity and plans for synthesis of more ligands based on the findings.

ENCAT has thus to date successfully developed and characterised new ligands for forming Schiff base-derived catalysts to be used with green solvents. This is a major step toward low-cost, environmentally friendly synthesis of asymmetric catalysts for a number of industrially relevant chemical reactions.