Diimine Explained

Diimines are organic compounds containing two imine (RCH=NR') groups. Common derivatives are 1,2-diimines and 1,3-diimines. These compounds are used as ligands, but they are also precursors to other organic compounds.[1]

Preparation

Diimines are prepared by condensation reactions where a dialdehyde or diketone is treated with amine and water is eliminated.[2] Many are derived from the condensation of 1,2-diketones and dialdehydes with amines, often anilines.[3] The dialdehyde glyoxal is an especially common precursor. Similar methods are used to prepare Schiff bases and oximes.

1,2-Diimines

The 1,2-diimines are also called α-diimines and 1,4-diazabutadienes. An example is glyoxal-bis(mesitylimine), a yellow solid that is synthesized by condensation of 2,4,6-trimethylaniline and glyoxal.[4] [2] 2,2'-Bipyridine is a 1,2-diimine.

1,2-Diketimines are “non-innocent ligands”, akin to the dithiolenes.[5]

1,3-Diimines

For example, acetylacetone (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 HNacNac, a modification of the abbreviation Hacac for the conjugate acid of acetylacetone. These species form bidentate anionic ligands.

Uses

Substituted α-diimine ligands are useful in the preparation of post-metallocene catalysts, which are used for the polymerization of alkenes.[6] [7]

1,2-Diimines are precursors to NHC ligands by condensation with formaldehyde.[4]

Reduction of 1,2-diimines gives diamines.[1]

References

  1. 10.15227/orgsyn.087.0077 . Microwave-Assisted Synthesis of 1,3-Dimesitylimidazolinium Chloride . Organic Syntheses . 2010 . 87 . 77. Morgan. Hans. Lionel. Delaude .
  2. 10.15227/orgsyn.084.0306 . Chiral Lithium Amide Base Desymmetrization of a Ring Fused Imide: Formation of (3aS,7aS)-2-[2-(3,4-Dimethoxyphenyl)-ethyl]-1,3-dioxo-octahydro-isoindole-3a-carboxylic Acid Methyl Ester . Organic Syntheses . 2007 . 84 . 306. Vincent . Rodeschini. Nigel S. . Simpkins. Fengzhi. Zhang .
  3. Wang. F.. Chen. C.. A Continuing Legend: The Brookhart-Type α-Diimine Nickel and Palladium Catalysts. Polymer Chemistry. 2019. 10. 19. 2354–2369. 10.1039/C9PY00226J. free.
  4. Elon A.. Ison. Ana. Ison. Synthesis of Well-Defined Copper N-Heterocyclic Carbene Complexes and Their Use as Catalysts for a "Click Reaction": A Multistep Experiment That Emphasizes the Role of Catalysis in Green Chemistry. J. Chem. Educ.. 2012. 89. 12. 1575–1577. 10.1021/ed300243s. 2012JChEd..89.1575I.
  5. 10.1246/bcsj.20200056. Redox-Active α-Diimine Complexes of Early Transition Metals: From Bonding to Catalysis. 2020. Mashima. Kazushi. Bulletin of the Chemical Society of Japan. 93. 6. 799–820.
  6. Ittel, S. D. . Johnson, L. K. . Brookhart, M. . Late-Metal Catalysts for Ethylene Homo- and Copolymerization . . 2000 . 100 . 4 . 1169–1203 . 10.1021/cr9804644. 11749263 .
  7. 10.1021/acscatal.5b02426. Palladium and Nickel Catalyzed Chain Walking Olefin Polymerization and Copolymerization. 2016. Guo. Lihua. Dai. Shengyu. Sui. Xuelin. Chen. Changle. ACS Catalysis. 6. 428–441. free.

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