Diimines are

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

s containing two

imine In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bon ...

(RCH=NR') groups. Common derivatives are 1,2-diimines and 1,3-diimines. These compounds are used as

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s, but they are also precursors to other organic compounds.

Preparation

Diimines are prepared by

condensation reaction In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a ...

s where a dialdehyde or diketone is treated with amine and water is eliminated. Many are derived from the condensation of 1,2-diketones and dialdehydes with amines, often

aniline Aniline (From , meaning ' indigo shrub', and ''-ine'' indicating a derived substance) is an organic compound with the formula . Consisting of a phenyl group () attached to an amino group (), aniline is the simplest aromatic amine. It is an in ...

s. The dialdehyde

glyoxal Glyoxal is an organic compound with the chemical formula OCHCHO. It is the smallest dialdehyde (a compound with two aldehyde groups). It is a crystalline solid, white at low temperatures and yellow near the melting point (15 °C). The liquid ...

is an especially common precursor. Similar methods are used to prepare

Schiff base In organic chemistry, a Schiff base (named after Hugo Schiff) is a compound with the general structure ( = alkyl or aryl, but not hydrogen). They can be considered a sub-class of imines, being either secondary ketimines or secondary aldim ...

s and

oxime In organic chemistry, an oxime is an organic compound belonging to the imines, with the general Chemical formula, formula , where R is an organic Side chain, side-chain and R' may be hydrogen, forming an aldoxime, or another organic functional g ...

1,2-Diimines

The 1,2-diimines are also called α-diimines and 1,4-diazabutadienes. An example is

glyoxal-bis(mesitylimine) Glyoxal-bis(mesitylimine) is an organic compound with the formula H2C2(NC6H2Me3)2 (Me = methyl). It is a yellow solid that is soluble in organic solvents. It is classified as a diimine ligand. It is used in coordination chemistry and homogeneous c ...

, a yellow solid that is synthesized by condensation of

2,4,6-trimethylaniline 2,4,6-Trimethylaniline is an organic compound with formula (CH3)3C6H2NH2. It is an aromatic amine that is of commercial interest as a precursor to dyes. It is prepared by selective nitration of mesitylene, avoiding oxidation of the methyl groups, ...

and

2,2'-Bipyridine The comma is a punctuation mark that appears in several variants in different languages. Some typefaces render it as a small line, slightly curved or straight, but inclined from the vertical; others give it the appearance of a miniature fille ...

is a 1,2-diimine. 1,2-Diketimines are “

non-innocent ligand In chemistry, a (redox) non-innocent ligand is a ligand in a metal complex where the oxidation state is not clear. Typically, complexes containing non-innocent ligands are redox active at mild potentials. The concept assumes that redox reactions ...

s”, akin to the

dithiolene Dithiolene metal complexes are complexes containing 1,2-dithiolene ligands. 1,2-Dithiolene ligands, a particular case of 1,2-dichalcogenolene species along with 1,2-diselenolene derivatives, are unsaturated bidentate ligand wherein the two dono ...

1,3-Diimines

For example,

acetylacetone Acetylacetone is an organic compound with the chemical formula . It is classified as a 1,3-diketone. It exists in equilibrium with a tautomer . The mixture is a colorless liquid. These tautomers interconvert so rapidly under most conditions that ...

(2,4-pentanedione) and a primary alkyl- or arylamine will react, typically in acidified ethanol, to form a diketimine. 1,3-Diketimines are often referred to as H

NacNac NacNac is a class of anionic bidentate ligands. 1,3-Diketimines are often referred to as "HNacNac", a modification of the abbreviation Hacetylacetone, acac used for 1,3-diketones. These species can exist as a mixture of tautomers. Preparation of ...

, a modification of the abbreviation Hacac for the conjugate acid of

. These species form bidentate anionic ligands.

Uses

Substituted α-diimine ligands are useful in the preparation of

post-metallocene catalyst A post-metallocene catalyst is a kind of catalyst for the polymerization of olefins, i.e., the industrial production of some of the most common plastics. "Post-metallocene" refers to a class of homogeneous catalysts that are not metallocenes. This ...

s, which are used for the

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

of alkenes.{{cite journal , doi=10.1021/acscatal.5b02426, title=Palladium and Nickel Catalyzed Chain Walking Olefin Polymerization and Copolymerization, year=2016, last1=Guo, first1=Lihua, last2=Dai, first2=Shengyu, last3=Sui, first3=Xuelin, last4=Chen, first4=Changle, journal=ACS Catalysis, volume=6, pages=428–441, doi-access=free 1,2-Diimines are precursors to

NHC ligand A persistent carbene (also known as stable carbene) is an organic molecule whose natural resonance structure has a carbon atom with incomplete octet (a carbene), but does not exhibit the tremendous instability typically associated with such moiet ...

s by condensation with formaldehyde. Reduction of 1,2-diimines gives diamines.

References

Imines Ligands