Cyclen
Chemical compound
From Wikipedia, the free encyclopedia
Cyclen (1,4,7,10-tetraazacyclododecane) is an aza-crown ether with the formula (CH2CH2NH)4. It is a white solid. It forms coordination complexes with metal cations and is used to synthesize the chelating agent DOTA which has several medical applications. Being structurally simple, symmetrical, and polyfunctional, cyclen has been widely investigated.[2]
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| Names | |
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| Preferred IUPAC name
1,4,7,10-Tetrazacyclododecane | |
| Other names
Tetraaza-12-crown-4 [12]aneN₄[1] | |
| Identifiers | |
3D model (JSmol) |
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| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.102.391 |
PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| C8H20N4 | |
| Molar mass | 172.276 g·mol−1 |
| Appearance | White solid |
| Melting point | 110–113 °C (230–235 °F; 383–386 K) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Synthesis
Some syntheses exploit the Thorpe-Ingold effect to facilitate ring-formation. Illustrative is the reaction of the deprotonated tosylamides with ditosylates:[3]
- TsN(CH2CH2NTsNa)2 + TsN(CH2CH2OTs)2 → (TsNCH2CH2)4
The resulting macrocycle can be deprotected with strong acid. Base gives the tetramine.
High dilution conditions result in a low reaction rate penalty and this disadvantage is removed in an alternative procedure starting from triethylenetetraamine and dithiooxamide to a bisamidine – also a bis(imidazoline) – followed by reduction and ring expansion with DIBAL.[4]
Coordination complexes
Coordination complexes of cyclen have been studied extensively.[6][7] With a 12-membered C8N4 ring, it tends to bind to four contiguous sites on octahedral metal centers, forming four 5-membered chelate rings (see figure). Cyclen also forms "bis complexes", e.g. of the type [Ln(cyclen)2]3+ where Ln = lanthanide.[8]
Related compounds
- The cyclam ligands are also tetraaza macrocycles but consist of a more flexible C10N4 ring.