Abstract
Salen ligands are a class of Schiff bases simply obtained through condensation of two molecules of a hydroxyl-substituted aryl aldehyde with an achiral or chiral diamine. The prototype salen, or N,N′-bis(salicylidene)ethylenediamine has a long history, as it was first reported in 1889, and immediately, some of its metal complexes were also described. Now, the salen ligands are a class of N,N,O,O tetradentate Schiff bases capable of coordinating many metal ions. The geometry and the stereogenic group inserted in the diamine backbone or aryl aldehyde backbone have been utilized in the past to efficiently transmit chiral information in a variety of different reactions. In this review we will summarize the important and recent achievements obtained in stereocontrolled reactions in which Al(salen) metal complexes are employed. Several other reviews devoted to the general applications and synthesis of chromium and other metal salens have already been published.
Highlights
Schiff bases are widely used as ligands in coordination chemistry and catalysis [1], and their complexes can be accessed by a variety of methodologies
As representative in the class of Schiff complexes, salen metal complexes have been explored in many applications, from material science and catalysis to coordination chemistry [2,3,4,5,6,7,8]
Oligomeric salen metal complexes perspective, oligomeric salen metal complexes were purposely designed for taking advantage of the were purposely designed for taking advantage of the bifunctional behavior (Figure 2)
Summary
Schiff bases are widely used as ligands in coordination chemistry and catalysis [1], and their complexes can be accessed by a variety of methodologies. Salen compounds are typically prepared by a condensation reaction between aromatic ortho-hydroxyaldehydes with primary 1,2-diamines in a 2:1 molar ratio respectively [5]. Both chiral and achiral salen Schiff bases are obtained by these methodologies. Salen are tetradentate ligands able to coordinate a variety of metals by subtle arrangement of the imine and hydroxyl group. What is especially important the stereochemical of the reaction is nature the salen outcome of the reaction is the salen metal for complex conformationoutcome that is influenced by the of metal complex conformation that is influenced by the nature of the ancillary toligands.
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