Diimine


Diimines are organic compounds containing two imine groups. The most popular derivatives are 1,2-diketones and 1,3-diimines. These compounds are used as ligands and as precursors to heterocycles. Diimines are prepared by condensation reactions where a dialdehyde or diketone is treated with amine and water is eliminated. Similar methods are used to prepare Schiff bases and oximes.

1,2-Diimines

The 1,2-diketimine ligands, also called α-diimines. They are derived from the condensation of 1,2-diketones with amines, using anilines.
An example is glyoxal-bis, a yellow solid that is synthesized by condensation of 2,4,6-trimethylaniline and glyoxal. 2,2'-Bipyridine is a 1,2-diimine.
1,2-Diketimines are “non-innocent ligands”, akin to the dithiolenes.

1,3-Diimines

For example, acetylacetone and a primary alkyl- or arylamine will react, typically in acidified ethanol, to form a diketimine.
1,3-Diketimines are often referred to as HNacNac, a modification of the abbreviation Hacac for the conjugate acid of acetylacetone. These species form anionic bidentate anionic ligands.

Uses

Substituted α-diimine ligands are useful in the preparation of so-called post-metallocene catalysts for the polymerization and copolymerization of ethylene and alkenes.
Diimines are precursors to NHC ligands by condensation with formaldehyde.