Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 169

Formation of chlorocatecholatoiron complexes and the oxygenative
decomposition with molecular oxygen were monitored by electronic absorption
spectroscopy and by product analysis. Interestingly dehydrochlroination
of the initial products was accompanied to give the products without the chloride
group. It was found that the addition of 2,6-lutidine as base is effective for
promotion of the oxygenation. The cleavage of chlorocatechols by nonheme iron
complexes indicated clearly that catechols for the model chemistry are not limited to
3,5-di- tert -butylcatechol and that iron complexes can oxygenate the catechols
having electron-withdrawing substituents. From the viewpoint of dehalogenation of
halogenated aromatic hydrocarbons, it is important to develop model systems that
decompose multi-halogenated catechols, e.g. dichlorocatechol and tetra-
chlorocatechol. Apart from the model oxygenations, Sorokin et al. developed
powerful catalysts for oxidation of tetrachlorocatechol to dichloromaleic acid by
using ironphthalocyanine in the presence of or percarbonate as an oxidant. 110

The catalyst oxygenates DTBC to give a furanone.
A new functional model chemistry on catechol dioxygenases has been
developed by Funabiki et al.. 111 Water-soluble ligands were prepared by sulfonation
of tripodal ligands such as TPA and used for catalytic oxygenation of water-soluble
catechols such as 4-

tert -butylcatechol, 4-chlorocatechol, and protocatechuic acid

(eq. 4).

Despite a typical substrate in the enzymatic system, protocatechuic acid was
found to be oxygenated by model complexes not in organic solvents but in water.
The highly selective and catalytic intradiol oxygenation of 4- tert -butylcatechol
indicated that various types of catechols other than 3,5-di- tert -butylcatechol can be
used as substrates in the model systems and that oxygenations by nonheme iron
systems in water are attractive. The reactivity and selectivity are dependent on the
substituent on catechols and of the solution.