Cyclen

Template:Chembox image cellTemplate:Chembox AllOtherNamesTemplate:Chembox headerbarTemplate:Chembox IndexlistTemplate:Chembox JmolTemplate:Chembox ChEMBLTemplate:Chembox ECHATemplate:Chembox E numberTemplate:Chembox IUPHAR ligandTemplate:Chembox UNIITemplate:Chembox CompToxTemplate:Chembox headerbarTemplate:Chembox Datapage checkTemplate:Chembox Footer

Cyclen

Template:Longitem	Template:Unbulleted list
ChEBI	Template:Unbulleted list
ChemSpider	Template:Unbulleted list
DrugBank	Template:Unbulleted list
EC Number	Template:Unbulleted list
KEGG	Template:Unbulleted list
Template:Longitem	Template:Unbulleted list
RTECS number	Template:Unbulleted list
Template:Longitem	Template:Chembox Elements/molecular formula
Molar mass	Template:Chem molar mass
Appearance	White solid
Melting point	Template:Chembox CalcTemperatures

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.

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.

Cyclen synthesis dithiooxamide method

Coordination complexes

File:CSD CIF JIKJUI.jpg

Structure of [Ni(cyclen)(OH₂)₂]²⁺. Color code: O = red, N = blue, Ni = dark blue, white = H, gray = C.

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.