Iron complexes carboxylates

Inspired by Gif or GoAgg type chemistry [77], iron carboxylates were investigated for the oxidation of cyclohexane, recently. For example, Schmid and coworkers showed that a hexanuclear iron /t-nitrobenzoate [Fe603(0H) (p-N02C6H4C00)n(dmf)4] with an unprecedented [Fe6 03(p3-0)(p2-0H)] " core is the most active catalyst [86]. In the oxidation of cyclohexane with only 0.3 mol% of the hexanuclear iron complex, total yields up to 30% of the corresponding alcohol and ketone were achieved with 50% H2O2 (5.5-8 equiv.) as terminal oxidant. The ratio of the obtained products was between 1 1 and 1 1.5 and suggests a Haber-Weiss radical chain mechanism [87, 88] or a cyclohexyl hydroperoxide as primary oxidation product. 

The geometry of the ferrous iron is trigonal bipyramidal. Thus, this structure confirms the tendency of iron complexes to coordination numbers higher than four. The two N-donors and one of the carboxylates of 5 occupy the equatorial positions. In good agreement... 

Shul pin and coworkers described the application of a di- and a tetranudear iron complex with triazacyclononane acetate ligands in the oxidation of alkanes and alcohols with H202 [47]. A highly complex tetranudear iron complex with octadentate pyridine carboxylate ligands was described by Gutkina et al. [48]. However, the TONs for cyclohexane oxidation did not exceed 5.0 in the latter case. 

Essentially on the basis of observations 1, 2, and 3, above, Warner 131) proposed the formula reproduced in Fig. 19. This formula for the iron complex involved three tyrosines and a carboxyl from the protein side chains and a bicarbonate. The copper complex was assumed to involve two tyrosines. 

The combination of bis[(2,6-carboxyl-carboxylato)pyri-dine]iron(n) [Fe (DPAH)2] and O2 results in the rapid autoxidation of the iron complex and is essentially unreactive with hydrocarbon substrates (e.g. c-CeH ). However, the presence of excess PhNHNHPh gives a system that is a hydrocarbon monooxygenase (C-C6H12c-CeHuOH). The distribution of R H isomers from 2-Me-butane indicates a selectivity in the order =CH > =CH2 > -CH3 the relative reactivities per C H bond are 1.00, 0.29, and 0.05, respectively. With Fe (PA)2/HOOH Fenton chemistry in 1.8 1 py/HOAc, the relative reactivities are 1.00, 0.43, and 0.07, and the values for aqueous HO- are 1.00, 0.48, and 0.10. Thus, the reactive intermediate from the Fe (DPAH)2/02/PhNHNHPh system is more selective than Fenton-derived and free HO-. 

Table 10 Quantum Yields for Photoreduction of Iron in Carboxylate Complexes at pH 2.7 and 4.0...

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