Oxidative aromatic ring cleavage of 3,5-di-t-butylcatechol, with total insertion of molecular oxygen, catalysed by 2,2′-bipyridine–iron(II) complex

Iron(III) complexes of certain meridionally coordinating tridentate ligands as models for non-heme iron enzymes: The role of carboxylate coordination

“…From our laboratory we have reported iron(III) complexes of linear tetradentate mono-and bis-phenolate ligands as structural and functional models for intradiol-cleaving enzymes and all of them exhibit intradiol cleavage activity [25,28]. In contrast to these model complexes those that elicit extradiol cleavage activity are fewer in number [29][30][31][32][33][34][35]. As five coordinate iron center is necessary for the extradiol cleavage, iron(III) complexes of tridentate ligands are of interest as they can bind to bidentate catecholate substrates.…”

Iron-Containing Models of Catechol Dioxygenases

“…Addition of bidentate it-acceptor ligands such as 2,2'-bipyridine and 1,10-phenanthroline is not essential for the reactions, but their presence increases the yields of the oxygenation reactions. 39 Because similar yields are achieved with either the iron(II) or iron(III) chloride salts 41 and because the same electronic absorption spectrum as that for the iron(III) solution was detected after exposure of the iron(II)-containing reaction mixture to an oxygen atmosphere, 40 it was concluded that the reaction proceeds through the same intermediate irrespective of the oxidation state of the utilized iron salt.…”

“…As previously mentioned, Funabiki et ai were able to demonstrate that, in addition to intradiol-cleavage products and the simple two-electron oxidation product dbq, extradiol-cleavage products are obtained in the reaction of H 2 dbc with dioxygen in the presence of catalytic amounts of iron(II) as well as of iron(III) salts. 39 "* 3 Mechanistic details are, however, still not resolved and the identity of the active species is unknown. Chiou and Que prepared the hydrogencatecholato iron(II) complex [Fe(6-Me 3 -tpa)(Hdbc)] + , which models the coordination mode of the catecholate in the enzyme-substrate complex of extradiol-cleaving catechol dioxygenases.…”

“…39 Within a series of publications, 39-43 they investigated the reaction of 3,5-di-/er/-butylcatechol H 2 dbc with molecular oxygen in various anhydrous solvents (THF, DMF, MeCN) that contain FeCl 2 -4H 2 0 or FeCl3 and an excess of a pyridine derivative. They observed a diversity of products in various yields, depending on the specific reaction conditions applied in the reactions (Reaction 8.4).…”

Oxygenative Cleavage of Chlorocatechols with Molecular Oxygen Catalyzed by Non-Heme Iron(III) Complexes and Its Relevance to Chlorocatechol Dioxygenases

“…[1] Various types of functional models for catechol dioxygenases have been described [10±23] since the first model oxygenation by a bipyridine(pyridine)iron complex was reported. [10,12] In these model studies 3,5-di-tertbutylcatechol (dtbc) was extensively used as a substrate, because the electron-donating substituents at the 3-and 5-positions facilitate the oxygenation of this catechol and prevent formation of polymer products. [24] Here we show that catechols with electron-withdrawing substituents can also be oxygenated catalytically by model iron complexes.…”