Coordination chemistry triazacyclononane

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

The coordination chemistry of the cyclic triamine 1,4,7-triazacyclononane ([9]aneN3 48h) has been studied by Wieghardt et al. and has proven to be a rich area. In aqueous solution, [9]aneN3... 

The dinucleating ligand (58) has been prepared by standard methods via the bis-hydroxymethyl-ation of 4R-substituted phenols. It has been observed that modification of the R substituent induces a drastic effect on the catecholase activity of the dicopper(II) complexes containing (58) in the deprotonated form.85 A similar coordination pattern to those found in metal derivatives of (58) is realized in bis(triazacyclononane) systems bridged by a m-xylyl fragment (59)86 and in (60).87 /)-Xylyl ligands exhibit different coordination chemistry and reactivity 85... 

The facially coordinating l,4,7-tiimethyl-l,4,7-triazacyclononane (Cn) ligand forms stable methylrhodium(III) complexes, such as [Rh(Me)3Cn], [Rh(Me)2Cn]OTf and [Rh(Me)Cn](OTf)2 (OTf=trifluoromethanesulfonate) and the latter two have rich aqueous chemistry. When dissolved in water, [Rh(Me)Cn] readily coordinates two water molecules to form the... 

Another way of bringing reactants into close proximity, which is encountered commonly in transition metal chemistry, is through metal ion complexation. The coordination of a reactant to a metal ion complex often activates its reactivity and can bring the reactant into close proximity with a second reactant or with a catalytic group. One example, shown in Fig. 6, is a zinc (11) complex of 1,5,9-triazacyclononane, as a model for the enzyme carbonic anhydrase, which contains a zinc (11) cofactor in its active site (4). In the aqua complex, the bound water molecule has a dramatically reduced pKa value of 7.3, which is similar to the pKa of the active site nucleophihc water. The corresponding cobalt (111) complex catalyzed ester hydrolysis at twice the rate because Co(lll) can coordinate both the hydroxide nucleophile and the ester carbonyl via a... 

---