Macrocycle nitrogen-donor

Complexes with macrocyclic nitrogen donor ligands 482... 

Complexes with Nitrogen Donor Ligands 63.5.2.1 Complexes with macrocyclic nitrogen donor ligands... 

The ligand L3 was initially intended to provide enforced tetrahedral coordination at the metal. Moore and co-workers (30,31) have successfully used the pendant arm macrocycle L5, also a derivative of [12]aneNs, for the same purpose (although in view of the foregoing discussion, enforcing the geometry may not have been necessary). The three macrocyclic nitrogen donors form the base of a tetrahedron and the pendant amine fills the apical site. If the pendant arm is shorter. 

Stability of Complexes of the Porphyrin TSPP Compared with the Nitrogen Donor Macrocycles Cyclam and THEC, with Metal Ions of Biological Interest"... 

Small-ring cyclic diamines have already been discussed in Chapter 1.20. The azamacrocycles offer the possibility for functionalization at the nitrogen donor groups and many examples will be presented from triazamacrocycles up to much larger polyaza macrocycles that will bind more than one zinc ion. Particular mention must be made of the large contribution of Kimura and co-workers to this area. 

The equilibrium constants, obtained by NMR spectroscopic methods, showed a strong dependence on both the macrocycles and the diorganozinc compounds. Polydentate nitrogen donor ligands, particularly triazacyclononanes, form much stronger complexes than cryptands and crown ethers. 

Other donor systems. Although not as common as all-nitrogen donor rings, macrocycles incorporating sulfur donor atoms have been widely reported. Structures (42)-(45) illustrate four representative examples of this type. 

Finally, the presence of the substituents on the nitrogen donors also influences the reactivity of the corresponding complexes significantly. Thus, utilization of the permethylated derivative in place of H2L23 drastically alters the Lewis-acidity of the metal ions, that is the coligands in the [Ni2(L19)(L )]+ compounds become more polarized than in the [Ni2(L23)(L )]+ complexes. In the latter complexes, the Lewis-acidity of the divalent nickel(II) ions is in large part consumed for the polarization of the six secondary NH functions. This explains why only the complexes of the permethylated macrocycle are able to activate and transform small molecules such as H20 or C02 (210,239,241). 

As with any metalloprotein, the chemical and physical properties of the metal ion in cytochromes are determined by the both the primary and secondary coordination spheres (58-60). The primary coordination sphere has two components, the heme macrocycle and the axial ligands, which directly affect the bound metal ion. The pyrrole nitrogen donors of the heme macrocycle that are influenced by the substitutents on the heme periphery establish the base heme properties. These properties are directly modulated by the number and type of axial ligands derived from the protein amino acids. Typical heme proteins utilize histidine, methionine, tyrosinate, and cysteinate ligands to affect five or six coordination at the metal center. 

LogX values for a number of tricarboxymethyl pendant arm derivatives of mixed oxygen nitrogen donor macrocycles have been reported. These include values of 16.09, 12.11, 14.44, and 9.47 for the ring systems (199), (200), (201a), and (201b), respectively. 

In the ternary complexes [Fe(127)(CN)2] the normally pentadentate macrocyclic aza-terimine ligand is only tetradentate, thanks to the particularly advantageous combined ligand field of two cyanide ligands and four nitrogen donor atoms in octahedral geometry. ... 

---