TAML ligand

Chart 1. Feni-TAML activators mentioned in this account are shown as pentacoordinated species with an axial aqua ligand as obtained in the solid state. The aqua complexes are synthesized as such or as the corresponding chloro species with Cl- instead of H20 (with two M+ = Li+, Na +, NR4 counter ions). The subscript Cl as in lei is used throughout to indicate the corresponding chloro species. 

Scheme 1. Speciation of Feni-TAML activators in aqueous solution (solid rectangle) and suggested mechanism of the H+-induced deme-talation (dashed rectangle) — — = free base ligand. From Ref. (13).

Equilibrium Constants for Fem-TAML Activators 1 Reacting with Ligands, L, in Aqueous Solution at 25°C, 0.1 M KPF0 (27)... 

Scheme 3. Stoichiometric mechanism of demetalation of robust FeIII-TAMLs such as lm by picolinic acid (L) in the presence of other pyridine bases (P). Axial aqua ligands are omitted for clarity.

Scheme 5. Speciation of oxidized TAML species derived from 1 in aqueous solution. Axial aqua ligands are not shown.

It is not known if the proposed 9 complex observed in nonaqueous solvents, is formed in water. An alternative formulation would have the hydroxo ligand still coordinated to iron and this hypothetical species 10 could also be deprotonated to give a ra zs-dioxo species. In fact, our mechanistic theory for the pH dependent rate of interaction Fem-TAML complexes with H202 is... 

Mechanistic studies, including density functional theory (DFT) calculations, reveal that M -peroxynitrite (M = Fe and Mn) species, generated in the reactions of [(TAML)Fem(02)] and [(TAML)MnIV(02)]2" with NO, are converted into MIV(0) and N02 species through 0-0 bond homolysis of the peroxynitrite ligand. Then, a rebound of Fe (O) with N02 affords... 

FIGURE 2.17 Correlation between DFT calculated and experimental isomer shifts at 4.2 K for TAML complexes.16 MAC, DMOB, and B are TAML variant ligands. 

FIGURE 1.3 Ligands used in various biomimetic catalytic systems, (a) Pydic = 2,6-pyridinedicar-boxylic acid (Beller) (b) TAML = tetraamido macrocyclic ligand = 3,3,6,6,9,9-hexamethyl-3,4, 8,9-tetrahydro-lH-l,4,8,ll-benzotetraazacyclotridecine-2,5,7,10(6H,llH)-tetraone (Que) (c) mep = N,N -dimethyl-N,N -bis(2-pyridylmethyl)-ethane (Jacobsen) and (d) phen = phenanthroline (Stack). 

Several interesting bleach catalysts are described in recent patent literature and are currently under evaluation. Fe-TAML (tetraamido macrocyclic ligand), for example, was selected from a large number of similar tetraamido complexes, and has excellent dye transfer inhibition properties, as it selectively destroys many dyes dissolved in the wash liquor [37]. The catalyst is being tested in several applications, such as effluent bleaching, the pulp and paper industry, desulfurization of diesel, and decontamination [38]. 

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