1,4,7-Triazacyclononane

1,4,7-Triazacyclononane, known as "TACN" which is pronounced "tack-en," is an aza-crown ether with the formula (C₂H₄NH)₃.^[1] 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, C₂H₄NH. Other members of the series include piperazine, C₄H₈(NH)₂, and the cyclic tetramer 1,4,7,10-tetraazacyclododecane.

1,4,7-Triazacyclononane

1,4,7-Triazacyclononane
Names
Preferred IUPAC name 1,4,7-Triazonane
Identifiers
CAS Number	4730-54-5 Y
3D model (JSmol)	Interactive image
Beilstein Reference	773877
ChEBI	CHEBI:37405 Y
ChEMBL	ChEMBL1650628
ChemSpider	163681 Y
ECHA InfoCard	100.164.887
EC Number	637-157-5
Gmelin Reference	2614
PubChem CID	188318
UNII	2UIF93C5H3 Y
CompTox Dashboard (EPA)	DTXSID50197095
InChI InChI=1S/C6H15N3/c1-2-8-5-6-9-4-3-7-1/h7-9H,1-6H2 Y Key: ITWBWJFEJCHKSN-UHFFFAOYSA-N Y InChI=1/C6H15N3/c1-2-8-5-6-9-4-3-7-1/h7-9H,1-6H2 Key: ITWBWJFEJCHKSN-UHFFFAOYAS
SMILES C1CNCCNCCN1
Properties
Chemical formula	C6H15N3
Molar mass	129.2046 g/mol
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314
Precautionary statements	P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Synthesis

The ligand is prepared from diethylene triamine as follows by macrocyclization using ethyleneglycol ditosylate.^[2]

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)]₃ + 2 NaOTs

[(CH₂CH₂N(Ts)]₃ + 3 H₂O → [CH₂CH₂NH]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)₃] and [(κ³-TACN)W(CO)₃]. Both have an oxidation state of zero. After further reacting with 30% H₂O₂, the products are [(κ³-TACN)MoO₃] and [(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, [κ³-TACN)Cu(II)Cl₂], a catalyst for hydrolytic cleavage of phosphodiester bonds in DNA,^[3] 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 of alkenes such as styrene using H₂O₂ as an oxidant in a carbonate buffered methanol solution at a pH of 8.0.  These reagents are considered environmentally benign,^[4]

[(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,^[5] e.g. yellow [(TACN)₂Cr]³⁺.^[6]