1.4.7- Tris 1,4,7-triazacyclononane

NiL2]2+-type sandwich complexes of tacn ligands bearing one or three pendent alkyne arms (L = /V,/V, /V"-tris(3-prop-1 -yne)-1,4,7-triazacyclononane or 7V-(4-but-2-yne)-1,4,7-triazacyclo-... 

Pendent arm 1,4,7-triazacyclononane macrocycles (91) and (92) have been used to stabilize the zinc-to-phenoxyl bond allowing characterization of these compounds.477 The interest in the zinc complexes comes from the wide potential range in which it is redox stable allowing observation of the ligand-based redox processes, this allows study of the radical by EPR and the electronic spectra is unperturbed by d-d transitions. Macrocycles of the type l,4,7-tris(2-hydroxybenzyl)-1,4,7-triazacylononane form a bound phenoxyl radical in a reversible one-electron oxidation of the ligand. The EPR, resonance Raman, electronic spectra, and crystal structure of the phenoxide complexes were reported. This compound can be compared to a zinc complex with a non-coordinated phenoxyl radical as a pendent from the ligand.735... 

An easily accessible hexadentate derivative of tacn, namely 1,4, 7-tris(u-aminobenzyl)- 1,4,7-triazacyclononane (tabtacn), forms a 1 1 complex [Cd(tabtacn)](C104)2 0.5 H20 Pc2 njPna2, Z = 4) with a distorted trigonal prismatic CdN6 core. The Cd—N bonds to the N donors in both the tacn moiety and in the aniline pendant arms are very similar in a rather narrow range (rav(Cd—N) 237 pm).178 Both solution and solid-state H, 13C, and 113Cd NMR spectra have been measured and analyzed with respect to details of the stereochemistry and to dynamics in solution. 

The octahedral complexes, pale green [VmL], purple VlvL]PF6, and blue-black [VvL](C104)2, where L represents a l,4,7-tris(2-hydroxybenzyl)-l,4,7-triazacyclononane derivative, serve as an example where all one-electron redox processes are clearly metal centered as depicted in Eq. (6). Table III lists the complexes prepared (148b, 152, 153). 

Fig. 5. Tris-aryloxide triazacyclononane ligand for uranium coordination chemistry.

The first successful isolation of a mononuclear uranium-tacn complex was achieved by treatment of the free l, 7-tris(3,5-di-fert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane (( ArOH)3tacn) (4 - ) (25) with one equivalent of [U(N(SiMe3)2)3] (35) in cold pentane... 

Under mildly basic conditions the manganese(II) species [MnLH3][MnCl4] [where LH3 = N,N N"-tris[(2S)-2-hydroxypropyl]-1,4,7-triazacyclononane (LH3)] partially deprotonates and on aerial... 

As a consequence of the presence of bulky Pr groups (and in contrast to the methyl substituted ligand species), the more sterically hindering ligand, A,A A"-tris[(2R)-2-hydroxy-3-methylbutyl]-1,4,7-triazacyclononane has been postulated to be unable to form a mixed-valence dinuclear species." Rather, the corresponding monomeric complex of type [Mn LJPFe was obtained and characterized by X-ray diffraction. 

The 1 1 complex of the tris-A-propionate derivative of 1,4,7-triazacyclononane has been synthesized and X-ray diffraction has confirmed that all ligand donors are bound to the manganese(III) ion surprisingly there was no evidence for a Jahn-Teller distortion of the type expected for a high-spin rf system of this type." ... 

Manganese(III) complexes of a number of phenolate pendant arm macrocycles related to the above have also been reported. Thus, both l,4,7-tris(2-hydroxybenzyl)-l,4,7-triazacyclononane and l,4,7-tris(3-t-butyl-2-hydroxybenzyl)-l,4,7-triazacyclononane, on tris-deprotonation, afford monomeric pseudooctahedral complexes with this ion." ... 

Tris-N-functionalization of 1,4,7-triazacyclononane has yielded a variety of sexadentate ligands, which form stable complexes with manganese(II). For example, the l,4,7-tris(2-pyridyl-methyl) derivative gives a complex of type [MnL](C104)2 in which the manganese ion has a... 

The potentially sexadentate macrocyclic ligands l,4,7-tris(3,5-dimethyl-2-hydroxybenzyl)-l,4,7-triazacyclononane (L H3), l,4,7-tris(3,5-di-t-butyl-2-hydroxybenzyl)-l,4,7-triazacyclononane (L"H3), and l,4,7-tris(3-t-butyl-5-methoxy-2-hydroxybenzyl)-l,4,7-triazacyclononane (L" H3) form the stable complexes of type [Mn L"]PF(5, [Mn L" ]PF(5 [M L "] [Mn L ]2(C104)3-(H30)(H20)3. These complexes were investigated by spectroelectrochemistry and were shown to undergo metal- and ligand-centered redox processes a phenoxyl radical Mn complex, [Mn L" ] +, was found to be accessible. 

Relative to the behavior of the 1,4,7-tris(carboxymethyl)-1,4,7-triazacyclononane ring, the contribution to Aml values of the 1,4,7-triazacyclononane fragment in the corresponding 1,4-bis(carboxymethyl)-1,4,7-triazacyclononane macrocycle is greater towards softer metal ions than towards harder ones such as manganese(ll). " ... 

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