Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 165

the analogous tripodal ligands L by the same research group: L
= PDA (R = COO - , R' = 2-pyridyl), BPG (R = 2-pyridyl, R' = COO - ), HDP (R = 2-
pyridyl, R' = 2-hydroxy-3,5-dimethylphenyl), 98 TPA (R = R' = 2-pyridyl). 99 The
high reactivity of the TPA complex towards was correlated with the stronger
iron-catecholate interaction compared with other complexes, resulting in the
enhanced covalency of the metal-catecholate bonds and low-energy catecholate
LMCT bands. 99 Some tripodal ligands are shown in Fig. 2.

Efforts were made to find a quantitative correlation between the reactivity of
the catecholate ligand with and Lewis acidity of the iron center. However, the
Lewis acidity which was originally introduced for the qualitative explanation is not
suitable for the quantitative treatment even though it is predicted on the
electrochemical (redox potential) or spectral data (LMCT band energies).
Viswanathan and Palaniandavar have found a good correlation between
and phenolate-to-iron(III) LMCT band energies in the series of complexes of
[Fe(L)DTBC] prepared in situ in methanol by using L which have two nitrogen
(amine, pyridine or imidazole) and one oxygen (phenol) for coordination (Fig. 3) : L
= N -(pyridin-2-ylmethyl)salicylideneamine, (2-hydroxy-5-nitrobenzyl)(pyridine-2-
ylmethyl)amine, (2-hydroxy-5-nitrobenzyl)(2-pyridin-2-ylethyl)amine, N- (2-