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

Final Report Summary - ENCAT (Synthesis of new Schiff base derived catalysts: application towards enantioselective reactions in greener and more sustainable media)

The epoxidation reaction is one of the most interesting and versatile tools in organic chemistry, especially in multi-step synthesis. Even if the epoxide is not the final target molecule, it gives access to numerous compounds. Its versatility comes from the fact that two potential stereogenic centres may be controlled in the same reaction. Considering this crucial importance, many catalytic systems and experimental conditions have been evaluated over the past 20 years. Unfortunately, the results obtained to date still suffer from major drawbacks. The latter are often related to a tedious and costly synthesis (i.e. porphyrins), a limited stability (i.e. salens) and/or require the use of non-environmentally friendly oxidant.

The ENCAT project (November 2009-October 2010) aimed at developing a new series of readily affordable ligands that could be used for complexing non-toxic metals and evaluate the catalytic activity of the new complex for the epoxidation of terminal olefins in an environmentally friendly medium.

To this end, we undertook the preparation of new pyrrole-containing salen type ligands that were hoped to display a catalytic activity as high as the parent salens whilst displaying an enhanced stability (Scheme 1). The synthetic strategy was validated and a series of three new ligands were prepared. The manganese complexes were synthesized and their catalytic activity was evaluated towards the H2O2 and PhIO-mediated epoxidations of three olefins, namely cyclooctene, styrene, and alpha-pinene. These studies revealed that:
1) these new systems display a strong catalase activity when H2O2 is used as terminal oxidant; and
2) a promising activity when PhIO is used as terminal oxidant (see the draft that has just been accepted for publication in Dalton Transactions).
Physicochemical characterisations were carried out by colleagues from the Inorganic Laboratory at the University of Orsay for understanding the intrinsic mechanisms and structural factors that control the catalytic activity. Based on those findings, the synthesis of a new series of ligands was planned but as Dr SZYDLO succeeded in getting a full-time job in a private company (early November 2010), the ENCAT project had to be ended by anticipation after 12 months. However, this project will be further continued in a different frame.