Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 175

temperature was observed with complex, that may be related to
the intense LMCT band throughout the temperature range. 145, 146
In the most mechanisms proposed for the intradiol cleavage oxygenations,
the direct attack of molecular oxygen upon a carbon atom attached with a phenolate
O atom is favored (substrate activation process, A in Fig. 8). The alternative
mechanism prefers the direct attack of to the iron center (oxygen activation

process, B in Fig. 8).

The A process is advantageous to explain the fact that even hexagonal
catecholatoiron complexes such as react with This reason,
however, is not applied to the enzymatic system since an open site becomes
available for the direct coordination of to the iron center by dissociation of the
Tyr ligand. One question arises whether the radical character of the aromatic carbon
is strong enough for the direct attack of About this question, Funabiki et al.

complexes by Extended-Hückel 148

studied on the catecholatoiron and density-

functional theory 149 analyses. Catecholato- and 3,5-di-methylcatecholato-
(n = 3 or 4) were used as model complexes for convenience. Atomic charge and
spin densities (spin, HOMO) of the dimethylcatecholate complex are followings.
O1: -0.58 (0.29, 0.14); O2: -0.56 (031, 0.18); Cl: +0.14 (0.043, 0.088); C2: +0.043
(0.059; 0.12); C3: +0.0017 (0.023, 0.024); C4: +0.037 (0.056, 0.075); C5 +0.076
(0.049, 0.082); C6: +0.035 (0.026, 0.0006); Fe: +1.38 (3.91, 0.023). It is apparent
that most of the negative and positive charges are located on O and Fe, respectively.
Carbons are slightly positively charged. Most of the spin density is also located on