Iron complex mononuclear

In addition to tri- [105] and tetradentate N-ligands, mononuclear and dinuclear iron complexes with pentadentate N,N,N,N,0-ligands were applied to alkane... 

A mononuclear diastereopure high-spin Fe alkylperoxo complex with a pen-tadentate N,N,N,0,0-ligand 33 (Scheme 17) was reported by Klein Gebbink and coworkers [109, 110]. The complex is characterized by unusual seven-coordinate geometry. However, in the oxidation of ethylbenzene the iron complex with 33 and TBHP yielded with large excess of substrate only low TON s (4) and low ee (6.5%) of 1-phenylethanol. 

DNICs are spontaneously [128] formed in aqueous media using a simple Fe(II) salt, S-nitrosothiol and thiol, with a ratio of Fe2+/RSH of 1 20. NO is transferred quantitatively from the sulfur atom in the RSNO to the iron. The complete mechanism is yet to be fully determined. A 1 2 ratio results in the formation of an EPR silent yellow dinuclear iron complex ([Fe2(RS)2(NO)4]. At the higherer ratio, the green paramagnetic, mononuclear dinitrosyl predominates. The reaction is very straightforward at pH 7.8, under an inert atmosphere and in water. Under anaerobic conditions the stability of this compound is enhanced, however, in the presence of air and hydrogen peroxide, it readily decomposes to give the dinuclear complex [126] which is similar in structure to the Roussin red salt, as shown in Scheme 5.5. 

The enzyme catalyzing the formation of retinal 2 by means of central cleavage of P-carotene 1 has been known to exist in many tissues for quite some time. Only recently, however, the active protein was identified in chicken intestinal mucosa (3) following an improvement of a novel isolation and purification protocol and was cloned in Escherichia coli and BHK cells (4,5). Iron was identified as the only metal ion associated with the (overexpressed) protein in a 1 1 stoichiometry and since a chromophore is absent in the protein heme coordination and/or iron complexation by tyrosine can be excluded. The structure of the catalytic center remains to be elucidated by X-ray crystallography but from the information available it was predicted that the active site contains a mononuclear iron complex presumably consisting of histidine residues. This suggestion has been confirmed by... 

Hydrothermal methods, for molecuarlar precursor transformation to materials, 12, 47 Hydrotris(3,5-diisopropylpyrazolyl)borate-containing acetylide, in iron complex, 6, 108 Hydrotris(3,5-dimethylpyrazolyl)borate groups, in rhodium Cp complexes, 7, 151 Hydrotris(pyrazolyl)borates in cobalt(II) complexes, 7, 16 for cobalt(II) complexes, 7, 16 in rhodium Cp complexes, 7, 151 Hydrovinylation, with transition metal catalysts, 10, 318 Hydroxides, info nickel complexes, 8, 59-60 Hydroxo complexes, with bis-Cp Ti(IV), 4, 586 Hydroxyalkenyl complexes, mononuclear Ru and Os compounds, 6, 404-405 a-Hydroxyalkylstannanes, preparation, 3, 822 y-Hydroxyalkynecarboxylate, isomerization, 10, 98 Hydroxyalkynes, in hexaruthenium carbido clusters, 6, 1015 a-Hydroxyallenes... 

Finally, we reported a di-iron(III) catalyst 24 and the corresponding copolymerization activity [147]. This system was able to produce copolymer with CHO/C02 and demonstrated a TOF of 53 h 1, at 80°C, lObar and aCHO/Fe ratio of 10,000 1. The system did not yield copolymer with PO, but addition of one equivalent of [PPN]C1, per Fe centre, allowed the conversion of PO into cyclic propylene carbonate with TOFs around 10 h 1. Previously, some heterobimetallic iron tert-butoxide complexes ( (7-BuO)5FeLa] and [(f-BuO)4FeZn]) had been reported for the copolymerization of PO and C02 [153]. This catalyst was the first use of an iron complex for the homogeneous copolymerization of CHO and C02. Rieger and coworkers recently reported a mononuclear Fe system that showed similar behaviour towards PO [154] and some copolymer formation with CHO/C02 strongly dependent on the co-catalyst system [98]. 

Suspected Si H—M interactions were also discussed in connection with the mononuclear complexes HReCp(CO)2(SiPh3) 161), HMnCp(CO)2(SiPh3) 161,162> and HFeCp(CO)2(SiF2Me)2 163>. From an analysis of known or estimated Si — H distances, it was concluded that Si — H interactions were most likely absent in the rhenium and iron complexes. In the case of HMnCp(CO)2(SiPh3), it was originally believed that a true example of Mn—H Si interaction existed162), but a subsequent re-assessment of the problem indicates that the structural evidence is, at best, inconclusive 161.163). 

All these reactions proceed most likely by initial activation of the iron(0) species by a ligand exchange with the activating additives, such as amines, benzonitrile or DMF (Fig. 7). Thus generated mononuclear iron complexes bearing a labile ligand are activated to form coordinatively unsaturated iron complexes 37A. These species reduce the polyhalo compounds to radicals 38A, which add to olefins 30 or 33. 

The main difference between mononuclear complexes containing either a M—H—C or a M—H—Si three-center bond is that most tj2-CH complexes correspond to an earlier stage of the addition reaction than do the 7j2-SiH complexes 7(CMH) coupling constants are usually closer to the values for /(OH), while /(SiMH) values are closer to 2/(SiMH), and the relative lengthening of the C—H distance on 172 coordination is usually smaller than that of coordinated Si—H bonds. For example, in the representative iron complex 21 [the structure of which was determined by neutron diffraction analysis (74)], the coordinated C—H bond... 

FeFe-enzyme - proton or hydrogen substrate binding and also the hydride-proton reaction exclusively occurs at the iron distal to the [4Fe-4S] cluster, suggesting that mononuclear iron complexes might also be viable catalysts. Consequently, Ott and coworkers have synthesized and characterized some stable pentacoordinated Fe(II) complexes with five ligands that nicely mimic the native ones and exhibit an open coordination site [163, 164]. This approach avoids the formation of the less reactive bridging hydrides that are found in the dinuclear complexes [153]. Catalytic H2 formation from weak acids at low overpotentials with promising TOF and catalyst stability could be demonstrated [164]. 

However, in acetonitrile with the ratio PhS Fe 5 1, the mononuclear tetrahedral iron complex [Fe(SPh)4]2 is formed first, which reacts with sulfur to form the iron(III) dimer [Fe SPh),]2-according to equations (67) and (68). No further reaction takes place, but addition of methanol facilitates the reductive elimination of PhSSPh from the dimer to give the 2Fen2FenI cubane complex as in equation (69). Although this series of reactions has been written for PhS-, it appears similar reactions take place with alkyl as well as aryl thiolates. 

Many of the structurally characterized -superoxo complexes are cobalt containing, or are iron complexes with sterically hindering porphyrins. Co compounds often react with dioxygen to form mononuclear superoxo complexes. 

The isolation of [Fe2(SMe)2(NO)4] from certain preserved vegetables and its implication in diet-related carcinogenesis, underlines the similarities between the iron- sulfur nitrosyl systems and the complexes discussed above. The proto-typic iron-sulfur nitrosyl complexes are Roussin s salts (Section Nitric Oxide Complexes with Sulfur Donors ). [Fe2 (SR)2 (N0)4] complexes are known with a wide range of R groups. They can be synthesized directly from iron(ll) salts, as shown in equation (20), or a variety of other mononuclear iron complex precursors including [Fe(NO)(S2CNMe2)2] (with excess RS ), [Fe(CO)3NO], and [Fe(NO)2(SR)2] . 

The mononuclear cobalt complexes are stable and are able to be isolated in both 2+ and 3+ oxidation states. Cyclic voltammetric studies reveal reversible waves for both Co " 2+ and Co + i reduction couples. These redox couples are shifted anodically as the ligand substituents are changed from methyl to phenyl. Electrolytic and cyclic voltammetric studies before and after electrolysis support the idea that the integrity of the complexes is maintained during electrolytic cycles of the 2+/3+ oxidation states. The IpJIpa values of the Co + 2+ couple for the binuclear cobalt complexes are identical to those observed for the oxidation of the analogous iron complex. Attempts to produce the binuclear cobalt(III) species by exhaustive electrolysis have been limited by adsorption of the cobalt(III) complexes on the electrode surface [186, 187],... 

It should be noticed that iron complexes produce mostly monocarbonyl compounds, while nickel complexes give dicarbonyl compounds. The difference between nickel and iron was explained by the structures of the mononuclear iron complex and the dinuclear nickel complex formed by the reactions of the metal carbonyls with phenyl lithium as shown below 92>. 

FeIII(PMA)]2 + A mononuclear nonheme-iron complex that catalyzes alkane oxidation. Inorg. Chem. 35, 6273-6281. 

The reactivity patterns for the alkane functionalization by iron(II) mononuclear complexes using H2O2 as terminal oxidant suggest that two reaction pathways are mainly associated with this type of chemistry one involving uncontrolled hydroxyl radicals, in particular produced by Haber-Weiss... 

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. 

Several iron complexes of tetradentate ligands containing pyridine arms have been reported to be able of carrying out olefin cis-hydroxylation and/or epoxidation in combination with H2O2 (90). In general, the cis-diol/epoxide ratio can be tuned by the nature of the metal coordination environment. Mononuclear iron(II) complexes of tetradentate ligands typically lead to... 

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