Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 167

constants with the optical parameters of the two LMCT O(DTBC) Fe(III) bands
was found except for (probably for the reason of steric
hindrance). The much lower activity of these complexes compared with
was ascribed to importance of the asymmetric coordination of
the DTBC ligand for the efficient intradiol cleavage.
The effect of substituents on the reactivity and the electronic state of the
catecholatoiron complexes were studied from different sides. Duda et al. have
synthesized the tripodal ligands with one (BPIA) or two (BIPA) methylimidazole
moieties (BPIA = bis[(2-pyridyl)methyl][(1-methylimiazol-2-yl)methyl]amine,
BIPA = bis[(1-methylimidazol-2-yl)methyl][(2-pyridyl)methyl]amine). 104-106 The
reactivity of oxygenation (pseudo-first order rate constants) of the complex,
decreased in the order of substituent on the catecholate
ligand, indicating that electron-donating
substituents on catechol result in a higher dioxygenase reactivity. The complexes
exhibit the lower reactivity than the TPA complex, and the rate constant

was

correlated with the lower energy LMCT band (nm): (4.3, 865),

(0.98, 842), (0.089, 729),

(0.015, 718).
Koch and Krüger developed a tetraazamacrocyclic ligand
= N,N' -dimethyl-2,11-diaza[3.3](2,5)pyridinophane) and reported the 54 turnovers in
the oxygenation of DTBCH 2 . 95 Mialane et al. synthesized an iron (III) complex,
with a doubly positively charged ligand (bispic-
= N,N' -bis(2-pyridylmehtyl)- N-N' -bis(5-trimethylammoniumpentyl)-1,2-
diaminoethane). 107 The complex in DMF reacts with at 20 °C to afford
selectively 3,5-di- tert -butyl-5-(carboxymethyl)-2-furanone (90%) after 48 h. The
effect of the O and N atom for the ligand coordination is the recent topics to be
clarified, because despite the Try and His ligands in enzymes no ligand having both
N and O atoms for coordination gives the higher activity than those having only N
atoms. 100, 102 Weiner and Finke developed a very unique system using all-inorganic
polyoxoanion as a ligand, that exhibits > 100,000 catalytic turnovers, e.g. by
as a prototype precatalyst. 108