Metal–Salen Schiff base complexes in catalysis: practical aspects

Abstract

Schiff base ligands are considered "privileged ligands" because they are easily prepared by the condensation between aldehydes and imines. Stereogenic centres or other elements of chirality (planes, axes) can be introduced in the synthetic design. Schiff base ligands are able to coordinate many different metals, and to stabilize them in various oxidation states, enabling the use of Schiff base metal complexes for a large variety of useful catalytic transformations. Practical guidelines for the preparation and use of different Schiff base metal complexes in the field of catalytic transformations are discussed in this tutorial review.

A Convenient Synthetic Route for the Preparation of Nonsymmetric Metallo‐salphen Complexes

“…This makes the salphen structure extremely useful for the creation of supramolecular materials and salphen-based homogeneous catalysts. [18] Studies along these lines are currently in progress in our laboratory.…”

The Supramolecular Attitude of Metal–Salophen and Metal–Salen Complexes

“…In salen complexes the absence or presence of an axially coordinating ligand can in general either reduce or enhance the folding of the metal complex, further influencing the transmission of chiral information. This is also supported by theoretical calculations showing that axial donor ligands (Figure 3), which modify the conformation of the complex, push the metal closer to the substrate, thus enhancing the enantioselectivity of the process [16]. Therefore, such feature can be looked at as a supramolecular effect since the presence, or the absence, of proper substituents can dramatically influence the enantioselectivity of the reaction.…”

Investigation of VO–salophen complexes electronic structure

“…The Schiff bases used for the synthesis of V IV O complexes were prepared from commercially available starting materials by the wellknown reaction between salicylaldehyde and a diamine [12,19].…”

“…Salen and salophen ligands are Schiff bases obtained from the easy condensation of two molecules of salicylaldehydes with ethylenediamine or o-phenylenediamine, respectively [12]. As Schiff bases, they are able to form stable complexes with different metals in various oxidation states.…”