Cyclen

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. : ==Coordination complexes==

File:CSD CIF JIKJUI.jpg|thumb|left|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 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. ==Related compounds==

• The cyclam ligands are also tetraaza macrocycles but consist of a more flexible C10N4 ring. == References ==