1,4,7-Triazacyclononane, known as "TACN" which is pronounced "tack-en," is an aza-crown ether with the formula (C₂H₄NH)₃. TACN is derived, formally speaking, from cyclononane by replacing three equidistant CH₂ groups with NH groups. TACN is one of the oligomers derived from

aziridine Aziridine is an organic compound consisting of the three-membered heterocycle . It is a colorless, toxic, volatile liquid that is of significant practical interest. Aziridine was discovered in 1888 by the chemist Siegmund Gabriel. Its deriva ...

, C₂H₄NH. Other members of the series include

piperazine Piperazine () is an organic compound with the formula . In term of its structure, it can be described as cyclohexane with the 1- and 4-CH2 groups replaced by NH. Piperazine exists as deliquescent solid with a saline taste. Piperazine is freely sol ...

, C₄H₈(NH)₂, and the cyclic tetramer 1,4,7,10-tetraazacyclododecane.

Synthesis

The ligand is prepared from diethylene triamine as follows by macrocyclization using ethyleneglycol ditosylate. :H₂NCH₂CH₂NHCH₂CH₂NH₂ + 3 TsCl → Ts(H)NCH₂CH₂N(Ts)CH₂CHH₂N(H)Ts + 3 HCl :Ts(H)NCH₂CH₂N(Ts)CH₂CH₂N(H)Ts + 2 NaOEt → Ts(Na)NCH₂CH₂N(Ts)CH₂CH₂N(Na)Ts :Ts(Na)NCHH₂CH₂N(Ts)CH₂CH₂N(Na)Ts + TsOCH₂CH₂OTs + → CH₂CH₂N(Ts)sub>3 + 2 NaOTs : CH₂CH₂N(Ts)sub>3 + 3 H₂O → H₂CH₂NHsub>3 + 3 HOTs

Coordination chemistry

TACN is a popular tridentate ligand. It is threefold symmetric and binds to one face of an octahedron of metalloids and transition metals. The (TACN)M unit is kinetically inert, allowing further synthetic transformations on the other coordination sites. A bulky analogue of TACN, is the N,N',N"-trimethylated analogue trimethyltriazacyclononane.

Illustrative complexes

*Although TACN characteristically coordinates to metals in mid- and high oxidation states, e.g. Ni(III), Mn(IV), Mo(III), W(III), exceptions occur. To illustrate, 1,4,7-triazacyclononane reacts readily with Mo(CO)₆ and W(CO)₆ to produce the respective air-stable tricarbonyl compounds, κ³ -TACN)Mo(CO)₃and κ³-TACN)W(CO)₃ Both have an oxidation state of zero. After further reacting with 30% H₂O₂, the products are κ³-TACN)MoO₃and κ³-TACN)WO₃ Both of these oxo complexes have an oxidation state of 6. The macrocyclic ligand does dissociate in the course of this dramatic change in formal oxidation state of the metal. *The complex, �³-TACN)Cu(II)Cl₂ a catalyst for hydrolytic cleavage of phosphodiester bonds in DNA, is prepared as follows from TACN trihydrochloride: :TACN·3HCl + CuCl₂·3H₂O + 3 NaOH → κ³-TACN)CuCl₂+ 6 H₂O + 3 NaCl *Mn-TACN complexes catalyze

epoxidation In organic chemistry, an epoxide is a cyclic ether, where the ether forms a three-atom ring: two atoms of carbon and one atom of oxygen. This triangular structure has substantial ring strain, making epoxides highly reactive, more so than other ...

alkene In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...

s such as

styrene Styrene is an organic compound with the chemical formula C6H5CH=CH2. Its structure consists of a vinyl group as substituent on benzene. Styrene is a colorless, oily liquid, although aged samples can appear yellowish. The compound evaporates easi ...

using H₂O₂ as an oxidant in a carbonate buffered

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

solution at a pH of 8.0. These reagents are considered environmentally benign, : κ³-TACN)Mn+ H₂O₂ + NaHCO₃ + (C₆H₅)C₂H₃→ κ³-TACN)Mn + 2H₂O + CO₂ + (C₆H₅)C₂H₂O *Chromium (II) sources, e.g. created by heating CrCl₃^.6H₂O in DMSO react with TACN to form both 1:1 Cr:and 2:1 complexes, e.g. yellow TACN)₂Crsup>3+.

References

{{DEFAULTSORT:Triazacyclononane, 1,4,7- Ethyleneamines Chelating agents Macrocycles Secondary amines Tridentate ligands