Triazacyclononane-containing ligands

Binuclear zinc complexes of triazacyclononane-containing ligands having different bridge structures (Fig. 71) exhibit second-order rate constants for HPNP transesterification that are only 3-5 times larger than that exhibited by the mononuclear [(L360H)Zn]2+ complex.256 This behavior is contrasted by that of... 

Fish reported that a Zn(ll)-imprinted resin, containing a sandwich arrangement of the well known 1,4,7-triazacyclononane (TACN) ligand, was found to be highly selective toward reintroduced Cu(II) in the presence of Fe(lll), Co(II), Ni(II), Zn(II) and Mn(II), after the removal of the Zn(II) template with 6 N HCl [36]. The following parameters were addressed structures of the monomers of the A-(4-vinyl-benzyl)TACN-Zn(II) complexes, polymerisation parameters, structure of the polymer TACN-template metal ion complex and selectivity to reintroduced metal... 

A third example of a polymeric ligand with pH-sensitive solubility is 97. This ligand was prepared by ring-opening metathesis polymerization of the 1,4,7-triazacyclononane-containing monomer 96 by the chemistry shown in Eq. 40 [132]. This polymer was capable of forming Mn(IV) complexes that oxidize alkenes and cycloalkanes with hydrogen peroxide. This basic polymer s solubility is affected by pH, as is the case with the other polymers 93 and 95 described above. 

A third example of a polymeric ligand with pH-sensitive solubility is 97. This ligand was prepared by ring-opening metathesis polymerization of the 1,4,7-triazacyclononane-containing monomer 96 by the chemistry shown in Eq. 40... 

Figure 11. Macrocyclic phenolate ligands containing a 1,4,7-triazacyclononane backbone (see Scheme 1 for an explanation of the abbreviations used).

L Ligands containing an 1,4,7-triazacyclononane backbone and one, two, or three phenol pendent arms. 

The first (phenoxyl)zinc(II) complexes have been prepared by using a similar strategy (143-145). Ligands containing a 1,4,7-triazacyclononane backbone and one, two, or three phenol pendent arms form very stable (phenolato)zinc(II) precursor complexes (Table II). Accordingly, their cyclic voltammograms display one, two or three reversible one-electron oxidation waves that in all cases have been shown by spectroelectrochemistry and/or EPR spectroscopy to be ligand based. 

L. Prodi, M. Maestri, R. Ziessel, and V. Balzani, Luminescent Eu3+, Tb3+, and Gd3+ complexes of a branched-triazacyclononane ligand containing three 2,2 -bipyridine units, Inorg. Chem. 30, 3798-3802(1991). 

The triazacyclononane ligand with o-aminophenylmethyl pendant arms (140) forms a bis-ligand complex with Fe +, isolated as its perchlorate. Aerial oxidation of this salt gives an uncharged iron(III) complex containing the ligand in triply-deprotonated form. ... 

The azamacrocycle 1,4,7-triazacyclononane (tacn) and its tris(A -methyl) analog (Me3tacn) are popular ligands in macrocyclic chemistry. Complexes of both and M (M = Ru, Os) containing the tacn ligand are dealt with together in this section along with several dinuclear, M—M bonded species. 

Scheme 2.5 Ligands used to synthesize structural and/or functional models for iron enzymes containing a 2-His-l-carboxylate facial triad (a) R3TACN (TACN = 1,4,7-triazacyclononane) [25] (b) TpR,R [differently substituted hydridotris(pyrazol-l-yl)borates] [27] (c) differently substituted bis(pyrazol-l-yl)acetates [29] (d) differently substituted 3,3-bis(1 -alkylimidazol-2-yl)propionates [30],...

Finally we note that enzymatic reduction of N02 and N03 is important in the natural nitrogen cycle. Copper-containing reductases are known and, as models, copper(I) nitrite complexes with triazacyclononane ligands have been shown to evolve NO.54... 

The Ta-Li alkylidene (29) (Section 4.2) containing an anionic triazacyclononane ligand (Pb2-tacn ) reacts with FeCl2(TEMDA) or [RhCl(COD)]2 to form bimetallic (90) and (91), respectively. In both products, the two metals in close proximity and linked by single-atom bridges. 

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