Cyclen

Synthesis

Some syntheses exploit the Thorpe-Ingold effect to facilitate ring-formation. Illustrative is the reaction of the deprotonated tosylamides with ditosylates: :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.

:[[Image:Cyclen synthesis dithiooxamide method.png|500px|Cyclen synthesis dithiooxamide method]]

Coordination complexes

Coordination complexes of cyclen have been studied extensively. With a 12-membered ring, it tends to bind to four contiguous sites on octahedral metal centers, forming four 4-membered rings (see example figure). In contrast the larger cyclam ligand forms complexes consisting of 4 coplanar rings.

Cyclen also forms complexes of the type [Ln(cyclen)2]3+ where Ln = lanthanide.

References

References

1. {{RedBook2005
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4. (2002). "1,4,7,10-Tetraazacyclododecane". Org. Synth..
5. (1990). "A Novel Conformation for a Coordinated Macrocycle: The Crystal Structure of [Ni(12-aneN₄)(OH₂)₂](CIO₄)₂·H₂O; (12-aneN₄= 1,4,7,10-Tetraazacyclododecane)". Journal of Coordination Chemistry.
6. (2005). "Responsive lanthanide luminescent cyclen complexes: From switching/Sensing to supramolecular architectures". Chemical Communications.
7. (2015). "Macrocyclic Metal Complexes for Metalloenzyme Mimicry and Sensor Development". Accounts of Chemical Research.
8. (2022). "Properties of Amine-Containing Ligands That Are Necessary for Visible-Light-Promoted Catalysis with Divalent Europium". Inorganic Chemistry.