Non-heme iron complex

Vanin, A. F., and Varich, V. Y. (1981). Nitrosyl non-heme iron complexes in animal tissues. Stud. Biophys. 86, 177-185. 

The antitumor antibiotic bleomycin (BLM) is believed to cause cytotoxicity through its ability, in the combined presence of dioxygen and a metal ion cofactor (204), to bind to and degrade DNA (205). Iron complexes of BLM have aroused special attention, as such complexes are the first (vide supra concerning the discussion of hemerythrin and hemocyanin) non-heme-iron complexes with a significant capacity for dioxygen activation (206). 

Non-heme Iron Complexes with Tetra- and Pentadentate Ligands... 

Two examples of non-heme iron complexes with tetradentate ligands should be presented, illustrating the problems associated with the use of such complexes for synthetic purposes. 

Clearly, while porphyrin complexes are obvious candidates for modelling these kinds of biomimetic oxidations, a range of non-heme iron complexes based on macrocyclic and podand ligand have also proved to be successful structural and functional mimics.19 To take one example, Figure 12.13 shows the X-ray structure of the iron (IV) tetramethylcyclam (tmc) oxo complex [Felv(tmc)(0)(MeCN)]2+... 

Olefin aziridination catalysts derived from other transition metals continue to be developed. Simple non-heme iron complexes have been reported to serve as effective... 

M. Klopstra, G. Roelfes, R. Hage, R. M. Kellogg, B. L. Feringa, Non-heme iron complexes for stereoselective oxidation Tuning of the selectivity in dihydroxylation using different solvents, Eur. J. Inorg. Chem. (2004) 846. 

G. Roelfes, V. Vrajmasu, K. Chen, R. Y. N. Ho, J.-U. Rohde, C. Zondervan, R. M. la Crois, E. P. Schudde, M. Lutz, A. L. Spek, R. Hage, B. L. Feringa, E. Miinck, L. Que, Jr., End-on and side-on peroxo derivatives of non-heme iron complexes with pentadentate ligands Models for putative intermediates in biological iron/dioxygen chemistry, Inorg. Chem. 42 (2003) 2639. 

There are few peroxide adducts of synthetic non-heme iron complexes that are well characterized (Table VI). Perhaps the best known adduct is that derived from Fe (EDTA) under basic conditions. This purple complex has an absorption maximum near 520 nm (e 528 M cm ) (163). These are absorptions characteristics associated with the peroxide-to-Fe" charge-transfer band in oxyHr however, the coordination mode of peroxide in the complex appears to be different from that in oxyFIr. After some debate in the literature, it has been concluded that the peroxide is T --bound on the basis of isotope effects observed in the Raman spectrum of the complex (158, 164). The v(O-O) of the H2 Oi complex is found at 815 cm". When is used, the v(O-O) shifts to 794 cm and appears as a peak of comparable line width. Were the peroxide only ri -bound, two peaks due to the Fe-O -O " and the Fe-" 0- 0 isotopomers would have been expected, as in oxyHr. An ri -peroxo structure is also proposed for [Fe(TPP)02] and has been determined for the corresponding [Mn(TPP)Oi] complex (165). 

In the last few years, several non-heme iron complexes have been identified as functional models for non-heme iron dioxygenases (85-88). These model complexes are able to catalyze the cis-dihydroxylation of olefins as well as the epoxidation of olefins using H2O2 as the primary oxidant. Table V presents the results of olefin oxidation by some representative mononuclear and dinuclear non-heme iron complexes in combination with H2O2. 

Catalysis of Olefin Oxidation by Some Representative Mononuclear and Dinuclear Non-Heme Iron Complexes in Using H2O2 as Oxidant... 

Fig. 15. Non-heme iron complexes as models for naphthalene 1,2-dioxygenase (88).

With regard to the biomimetic non-heme iron complexes, the work devoted to develop catalysts that perform catalytic alkane hydroxylation has resulted in a large number of iron complexes, which generate Fe =0 iron-oxo species characterized by different spectroscopic techniques. There is now direct evidence that the involvement of high-valent iron-oxo species leads to stereospecific alkane hydroxylation, while hydroxyl radicals contribute to non-selective oxidations. The impressive work performed by Que and co-workers has demonstrated that olefin epoxidation and cis-dihydroxylation are different facets of the reactivity of a common Fe -OOH intermediate, whose spin state can be modulated by the electronic and steric properties of... 

Because of the success with iron cyclam, our search for other non-heme iron complexes involved a survey of cyclam like ligands including HMCD (5,7,7,12,14,14-hexamethyl-l,4,8,ll-tetraazocyclodec-4,l 1-diene), TIM (2,4,9,10-tetramethyl-l,4,8,ll-tetraazocyclodec-l,3,8,ll-tetraene), TDO (1,4,8,ll-tetraazocyclodecane-5,7-dione), etc. Under the same reaction conditions as for iron cyclam, the iron complexes of these other ligands also proved to be efficient catalysts for olefin epoxidation with PhIO and MCPBA, but not for H2O2. These results further support the notion that the three oxidants behave differently in their reactions with these non-heme iron complexes. 

Reginato N, McCrory CTC et al (1999) Synthesis, X-ray crystal structure, and solution behavior of Fe (NO)2 (1-Melm)2 implications for nitrosyl non-heme-iron complexes with g = 2.03. J Am Chem Soc 121 10217-10218... 

Hgure 6 ESR spectra of liver tissue from mice at 77 K (A) control animal on normal diet (B) mouse on drinking water with 0.3% nitrite for 7 days. The nitrite consumption induces formation of dinitrosyl-iron (DNIC 0.03) and nitrosyl-heme complexes, at g=1.98. (Reproduced with permission from Varich V (1979) Changes in amounts of dinitrosyl non-heme iron complexes in animal tissues depending on animal growth. Biofyzika (Russian) 24 344-347.)... 

Burbaev, D.Sh. (1971) An EPR study q/ compounds modeling non-heme iron complexes in biological systems, PhD. Thesis, Moscow State University. 

An additional contribution to the field ofbiomimetic non-heme iron complexes for alkene oxidation was recently reported by Klein Gebbink and coworkers [109]. They found that iron(II) complexes formed with the neutral ligand propyl 3,3-bis(l-methylimidazol-l-yl)propionate (20) were active as catalysts for the oxidation of various simple alkenes. When complex 21 was employed as the catalyst for the oxidation of cyclooctene in the presence of 10 equivalents of hydrogen peroxide, a mixture of epoxide and diol in a ratio of 2.5 1 was obtained. However, the conversion was rather poor (39%). 

Another compound which has been found to somewhat imitate the active site of peroxidases is the commercially available Fe(II)-salen catalyst. This catalyst was used successfully to produce phenol polymers, which could be of interest for industrial production [153,154]. For example, cardanol can be polymerized by the Fe(II)-salen catalyst [155]. Due to the unsaturated bonds in the side chain of the cardanol components, the resulting polymers could be thermally cured, or cured by use of cobalt naphthenate to give brilliant films with a high-gloss surface. This reaction proves that reactive prepolymers can be synthesized from renewable resources (cardanol is the main component obtained by thermal treatment of cashew nutshell liquid). This process could be a true alternative to conventional phenol-formaldehyde resins (Scheme 25) [ 155]. Other non-heme iron complexes have been foimd to... 

In a historical view, early model systems mimicking the P-450 type reactions consisted of non-heme iron complexes/02 in the presence of reducing agents, since the typical feature of monooxygenase reactions was believed to be the reductive oxygen activation with stoichiometry as depicted in Scheme 1 [1-3, 20-22]. For example, Udenfriend et al found the combination of Fe(II) perchlorate with ascorbic acid and O2 was capable of oxidizing... 

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