**1. Introduction**

In the year 1864, Hugo Schiff was the first to synthesize Schiff's base under azeotropic distillation by using aldehyde or ketone and primary amine. They can be considered a sub-class of imines with the general structure R1R2C∙NR′ (R′ ≠ H) [1–5]. Depending on their structure, they can be considered as either secondary aldimines or secondary ketimines. When these compounds are being used as ligands to form coordination complexes with metal ions, the term Schiff base is applied. Corrin complexes occur naturally, but the majority of artificial Schiff bases are used to form many important catalysts, such as Jacobsen's catalyst (**Figure 1**).

Schiff bases are imines in which R3 is an alkyl or aryl group (not hydrogen). R1 and R2 may be hydrogen. Schiff bases have a wide range of biological properties such as antimicrobial, anticancer, and antiviral. Inhibition of amyloid-β aggregation is achieved by Schiff bases [6]. They are common enzymatic intermediates where an aldehyde or ketone of a cofactor or substrate reversibly reacts with the terminal group of a lysine residue. Lysine residue forms a Schiff base with the common enzyme cofactor pyridoxal phosphate (PLP) and is transaldiminated to the substrate(s) [7]. Similarly, the cofactor retinal forms a Schiff base in human rhodopsin (via Lysine 296), which is key in the photoreception mechanism.

In coordination chemistry, Schiff bases are common ligands. The ligands are derived from aromatic aldehydes and alkyl diamines [8]. The imine nitrogen is

**Figure 1.** *General structure of an imine.*

**Figure 2.** *Copper (II) complex of the Schiff base ligand salicylaldoxime.*

basic in nature and exhibits pi-acceptor properties. In 1968, Ryōji Noyori was awarded a share of the 2001 Nobel Prize in Chemistry for the development of a copper-Schiff base complex for the metal-carbenoid cyclopropanation of styrene (**Figures 2**–**4**) [9].

*Introduction to Schiff Base DOI: http://dx.doi.org/10.5772/intechopen.108289*

**Figure 4.** *Jacobsen's catalyst is derived from a chiral Salen ligand.*
