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 A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or ...

with metal

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

and is used to synthesize the

chelating agent Chelation () is a type of bonding of ions and their molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These l ...

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which has several medical applications. Being structurally simple, symmetrical, and polyfunctional, cyclen has been widely investigated.

Synthesis

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

tosylate In organic chemistry, a toluenesulfonyl group (tosyl group, abbreviated Ts or TosIn this article, "Ts", unless otherwise stated, means tosyl, not tennessine.) is a univalent functional group with the chemical formula . It consists of a tolyl ...

s: :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 Triethylenetetramine (TETA and trien), also known as trientine (INN) when used medically, is an organic compound with the formula H2NHCH2CH2NH2sub>2. The pure free base is a colorless oily liquid, but, like many amines, older samples assume a yel ...

and dithiooxamide to a bisamidine – also a bis(

imidazoline Imidazoline is a heterocycle formally derived from imidazole by the reduction of one of the two double bonds. Three isomers are known, 2-imidazolines, 3-imidazolines, and 4-imidazolines. The 2- and 3-imidazolines contain an imine center, whereas t ...

) – followed by reduction and ring expansion with DIBAL. :

Coordination complexes

Coordination complex A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

es 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 Cyclam (1,4,8,11-tetraazacyclotetradecane) is an organic compound with the formula (NHCH2CH2NHCH2CH2CH2)2. Classified as an aza-crown ether, it is a white solid that is soluble in water. As a macrocyclic ligand, it binds strongly to many transit ...

ligand forms complexes consisting of 4 coplanar rings. Cyclen also forms complexes of the type n(cyclen)₂sup>3+ where Ln =

lanthanide The lanthanide () or lanthanoid () series of chemical elements comprises at least the 14 metallic chemical elements with atomic numbers 57–70, from lanthanum through ytterbium. In the periodic table, they fill the 4f orbitals. Lutetium (el ...

Synthesis

Coordination complexes

References

Further reading