Fluorinated salen ligands

The limitations of the system with regard to substrates and oxidants was attributed to the strong electron-withdrawing character of the perfluorinated chains and the lower steric hindrance in the position adjacent to phenols, in marked contrast to the ferf-butyl groups present in Jacobsen s catalyst, hi view of this, a second generation of fluorinated salen ligands le and If was... 

Only a few years after the development of the homogeneous chiral Mn(salen) complexes by Jacobsen and Katsuki, several research groups began to study different immobiUzation methods in both liquid and soUd phases. Fluorinated organic solvents were the first type of Uquid supports studied for this purpose. The main problem in the appUcation of this methodology is the low solubility of the catalytic complex in the fluorous phase. Several papers were pubUshed by Pozzi and coworkers, who prepared a variety of salen ligands with perfluorinated chains in positions 3 and 5 of the saUcyUdene moiety (Fig. 2). 

In contrast with salen ligands, ionic liquids were used earlier than fluorinated solvents for biphasic liquid systems with bis(oxazoline)-based complexes. In... 

Cobalt tetraarylporphyrins with fluorine-containing substituents were active in epoxidation of alkenes using fluorous catalysis in the presence of oxygen and 2-methylpropanal [167,170-171]. Manganese and cobalt complexes of perfluorinated tetraazocyclonone catalyzed allylic oxidation of alkenes with r-BuOOH/Oa [172]. The complex with the salen ligand 57 was active in alkene epoxidation under Mikayama s conditions, and indene was epoxidated at a high stereospecificity [173]. 

Asymmetric aldolization of a-isocyanoacetamide and fluorinated benzaldehydes has been realized with a gold(I) salt and a ferrocenyl amine-phosphine ligand. (Salen)-Ti complexes serve well in catalyzing the condensation of diketene with aldehydes. " A camphor lactam is an adequate chiral auxiliary as its derived imide undergoes asymmetric aldol reactions. 

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