Chemical Basis for High Activity in Oxygenation of Cyclohexane Catalyzed by Dinuclear Iron(III) Complexes with Ethereal Oxygen Containing Ligand and Hydrogen Peroxide System

Abstract

The crystal structures of two binuclear iron(III) complexes with linear μ-oxo bridge, Fe2OCl2 (tfpy)2 (ClO4)2 ·2CH3CN and Fe2OCl2(epy)2(ClO4)2 were determined, where (tfpy) and (epy) represent N,N-bis(2-pyridylmethyl)-tetrahydrofurfurylamine and N,N-bis(2-pyridylmethyl)-2-ethoxyethylamine, respectively. Their structural features are essentially the same as that of the corresponding linear binuclear complex with (tpa)-complex, Fe2OCl2(tpa)2(ClO4)2, where (tpa) is tris(2-pyridylmethyl)amine; the ligands (tfpy) and (epy) act as a tetradentate tripod-like ligand, and Fe-O (ethereal oxygen atom; these are located at the trans-position of bridging oxo-oxygen atom) distances are 2.209(4) and 2.264(2) Å for (tfpy) and (epy) compounds, respectively. These two (tfpy) and (epy) complexes exhibited much higher activity for the oxygenation of cyclohexane in the presence of hydrogen peroxide than that of the (tpa) complex. In contrast to this, the former two complexes exhibit negligible activity for the decomposition of hydrogen peroxide, whereas the catalase-like function of the (tpa) compound is remarkable. These are indicating that an active species for oxygenation of cyclohexane, which is assumed to be an iron(III)-hydroperoxide adduct with η1-coordina­tion mode, should be different from that is operating for decomposition of hydrogen perox­ide; for the latter case formation of a (μ-η1:η1-peroxo)diiron(III) species being stressed. The EHMO calculation showed that electronic interaction between the monodentate hydroperox­ide adduct of the binuclear iron(IIl)-(tfpy) compound and the tetrahydrofuran ring of the ligand system may lead to facile peroxide-tetrahydrofuran linkage formation, and the interac­tion described above should promote the O-O cleavage of the peroxide ion heterolytically. Based on these discussions, it was concluded that heterolytic O-O bond cleavage of the iron(III)-hydroperoxide adduct caused by electronic interaction with organic moiety contain­ing an ethereal-oxygen and by approach of the substrate which donates electron to the perox­ide adduct should play an important role in producing a high-valent iron-oxo species in these systems. In the case of (tpa) complex, formation of a hydroperoxide adduct linking with the ligand system seems to be unfavorable because of both the steric and electronic reasons.

Interaction between the Peroxide Adduct of Binuclear Iron(III) Complex with (HPTP) Anion and the Sugar Moiety of Nucleosides

“…3), since it prevents the approach of another hydrogen peroxide molecule to the peroxide adduct. In the figure below, it seems quite likely that elec tronic interaction [18] occurs between the terminal oxygen atom of the peroxide ion and carbon atom of C4'-position (llll denotes the presence of elec tronic interaction; here the peroxide adduct acts as an electrophile [18]): base This may be consistent with the fact the Fe2(HPTP)Cl4+ complex shows high ability to gen erate 7 -butyrolactone and 2 -hydroperoxide-tetrahydrofuran in the reaction with THF and hydrogen peroxide (see Fig. 5).…”

Deposition of Iron(III) Hydroxide on Aggregations of Several Proteins

“…7.5 (for H 2 ida, see Figure 1). The structural data of this complex [11] suggests that the precipitation of iron(III) hydroxide and dissociation of the (H 2 ida) from the [Fe 2 O(ida) 4 ] 42 above 408C may be due to a weak Fe-O bond (1.796 Å at 238C, see Figure 3) compared with the analogous stable compounds containing a linear oxo-bridge structure (Fe-O, 1.78 Å ), [9] and weakening of the Fe-O bond in this compound should be attributed to the coordination of the second (ida) molecule (coordinated by N2 and O7 in Figure 3); this is supported by the fact that the corresponding iron(III) species with [ida]/[Fe 3þ ] ¼ 1, which does not contain the second (ida) molecule in Figure 3, is stable under the same experimental conditions. Based on the preceding discussion we may conclude that deposition of the iron(III) hydroxide observed in this study proceeds via coordination of oxygen atoms of the aggregations of peptides, aggregation formation is greatly promoted by zinc(II) ion, to the iron(III) ion as illustrated in Figure 4.…”

“…The insoluble brown precipitates do not contain the (H 3 hida). While the solution of the iron(III) chelates with (H 2 edda), (H 3 hida) or (H 3 nta), containing a bent-Fe-O-Fe structure, [9,10] is green, the precipitated species is always brown. All these facts suggest that deposited brown substance observed in this study is the iron(III) hydroxide.…”

μ-Oxo-bis{chloro[N-(2-methoxyethyl)-N,N-bis(pyridin-2-ylmethyl)amine-κ4-N,N′,N′′,O]iron(III)} bis(trifluoromethanesulfonate) acetonitrile disolvate

“…The title compound, (I), was obtained by acid-base self-assembly synthesis during attempts to prepare chloride-free -oxodiiron(III) complexes with the ligand N-(2-methoxyethyl)-N,Nbis(pyridin-2-ylmethyl)amine (abbreviated as mebpa). Previously, the crystal structures of the dinuclear iron complex with perchlorate counter-ions were reported by Nishida et al (1995), Ito et al (1997) and Tanase et al (2004). No atomic coordinates are available for the first two structures.…”