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Aza-crown ether

Ring molecule with several amine (–N– or >N–) groups

Aza-crown ether
Summary

Ring molecule with several amine (–N– or >N–) groups

pages=459–463}}</ref> Color code: blue = N, gray = C, black = C, white = H.

In organic chemistry, an aza-crown ether is an aza analogue of a crown ether (cyclic polyether). That is, it has a nitrogen atom (amine linkage, or ) in place of each oxygen atom (ether linkage, ) around the ring. While the parent crown ethers have the formulae , the parent aza-crown ethers have the formulae , where n = 3, 4, 5, 6. Well-studied aza crowns include triazacyclononane (n = 3), cyclen (n = 4), and hexaaza-18-crown-6 (n = 6).

File:Me3TACN.png|1,4,7-Trimethyl-1,4,7-triazacyclononane, a tridentate ligand used in coordination chemistry. File:Cyclam.png|Cyclam is a tetraaza crown ether with alternating and linkers between amine centers. File:Plerixafor.svg|Plerixafor, a derivative of cyclam, is used to mobilize blood stem cells as a part of blood cancer treatment. File:Cryptand.svg| 2.2.2-Cryptand is an aza-crown of the mixed ether-amine variety.

Synthesis

The synthesis of aza crown ethers are subject to the challenges associated with the preparation of macrocycles. The 18-membered ring in (CH2CH2NH)6 can be synthesized by combining two triamine components. By reaction with tosyl chloride, diethylene triamine is converted to a derivative with two secondary sulfonamides. This compound serves as a building block for macrocyclizations.

Variants

Many kinds of aza crown ethers exist. ;Variable length linkers: Aza crowns often feature trimethylene ((CH2)3) as well as ethylene ((CH2)2) linkages. One example is cyclam (1,4,8,11-tetraazacyclotetradecane).

;Tertiary amines: In many aza-crown ethers some or all of the amines are tertiary. One example is the tri(tertiary amine) (CH2CH2NCH3)3, known as trimethyltriazacyclononane. Cryptands, three-dimensional aza crowns, feature tertiary amines.

;Mixed ether-amine ligands: Another large class of macrocyclic ligands feature both ether and amines. One example is the diaza-18-crown-6, [(CH2CH2O)2(CH2CH2NH)]2.

;Lariat crowns: The presence of the amine allows the formation of Lariat crown ethers, which feature sidearms that augment complexation of cation.

References

References

  1. (1992). "Electron-density distribution in crystals of 1,4,7,10,13,16-hexaazacyclooctadecanecobalt(III) trichloride, meso-[Co(hexaen)]Cl3 at 106 K". Acta Crystallographica Section B: Structural Science.
  2. (1999). "Proton coordination by polyamine compounds in aqueous solution". Coordination Chemistry Reviews.
  3. (2002). "Metal complexes of azacrown ethers in molecular recognition and catalysis". Journal of the Chemical Society, Dalton Transactions.
  4. (2002). "1,4,7,10-Tetraazacyclododecane". Org. Synth..
  5. (2007). "Plerixafor". Drugs in R&D.
  6. (1989). "Synthesis of aza-crown ethers". Chemical Reviews.
  7. (1978). "1,4,7,10,13,16-Hexaazacyclooctadecane". Org. Synth..
  8. (1971). "Stability constants of cyclic polyether complexes with univalent cations". Journal of the American Chemical Society.
  9. (1990). "4,13-Diaza-18-Crown-6". Organic Syntheses.
  10. (2002). "Lariat Ether Receptor Systems Show Experimental Evidence for Alkali Metal Cation Interactions". Acc. Chem. Res..
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polyamines secondary-amines tertiary-amines 1,2-ethanediyl-compounds chelating-agents macrocycles
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