Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 171

cleavage with a small extent of extradiol cleavage (89 : 3 or 78 : 12). Weiner et al.
developed polyoxoanion-supported Fe(II) complex that produces the extradiol
cleavage products ( ca. 52%) together with DTBQ (40%). 118 All-inorganic
polyoxoanion as oxidation-resistant ligand forms a Fe(II)-DTBC species that binds
with to form 1:1:1 species (volumetric titration) as shown in Fig. 5. The
oxygen species decomposes very slowly to give oxygenated products. No
explanation has been given to the very slow (7 days) oxygenation of DTBC, but the
system gives an example of catalytic dioxygenase-like system without the need to
worry about catalyst lifetime-limiting, ligand-oxidation side reactions.

Instead of the use of complexes, the extradiol oxygenation by
complexes has been studied. 90, 119, 120 This mimics the function of the
containing enzymes that produce the extradiol oxygenation products from some
catechols. 60-62 Dei et al. synthesized tri- and tetra-azamacrocyclic ligands and
studied the reactivity of the complexes with oxygen, and reported that
the complex in acetonitrile yielded 3,5-bis(1,1-
dimethylethyl)-2 H -pyranone (30%) and 4,6-bis(1,1-dimethylethyl)-2 H -pyranone
(5%) by the extradiol cleavage in addition to DTBQ (65%) (eq. 5). 90

Ito et al. used (but not AgOAc) to remove the chloride from the same
complex and found that the extradiol cleavage products, two isomeric di- tert -butyl-
2-pyrones, can be selectively produced (76 : 16). 119 It is characteristic that the
intradiol cleavage products are formed in only trace amounts. Ogihara et al. used
the hydrotris(pyrazolyl)borate ligand to synthesize a five-coordinate