Iron complexes decomposition

One-step hydroxylation of aromatic nucleus with nitrous oxide (N2O) is among recently discovered organic reactions. A high eflSciency of FeZSM-5 zeolites in this reaction relates to a pronounced biomimetic-type activity of iron complexes stabilized in ZSM-5 matrix. N2O decomposition on these complexes produces particular atomic oj gen form (a-oxygen), whose chemistry is similar to that performed by the active oxygen of enzyme monooxygenases. Room temperature oxidation reactions of a-oxygen as well as the data on the kinetic isotope effect and Moessbauer spectroscopy show FeZSM-5 zeolite to be a successfiil biomimetic model. 

Copper catalyzes the decomposition of sulphonyl azides in benzene very slowly. When methanesulphonyl azide was boiled under reflux in benzene solution in the presence of an excess of freshly reduced copper powder, some decomposition occurred to give methanesulphonamide and azide was recovered 78>. Transition metal complexes have been found to exert a marked effect upon the yields of products and isomer ratios formed in the thermal decomposition of methanesulphonyl azide in methyl benzoate and in benzotrifluoride 36>. These results will be discussed in detail in the section on the properties of sulphonyl nitrenes and singlet and triplet behaviour. A sulphonyl nitrene-iron complex has recently been isolated 37> and more on this species will be reported soon. 

The thermal decomposition of iron complexes leading to the formation of different ferrites (MFe204, M = Fe, Co, Mn, etc.) is one of the most commonly used protocols to obtain magnetic NPs with control of size and shape [39]. However, some of them cannot be considered as green processes since the iron precursor, the Fe(CO)5 complex, is expensive, toxic, and flammable. Therefore, researchers have looked for non-toxic and less expensive iron precursors to be used in the thermal decomposition reactions. The first precursor in substitution of Fe(CO)5 was the FeCup3... 

N20 decomposition over (p-oxo)(p-hydroxo)di-iron complex supported by ZSM-5 zeolite effect of cluster size on DFT energy profile... 

In contrast to the reaction of an i72-CS2-rhodium complex with dimethyl acetylenedicarboxylate which gives rise to a metallocycle,186 the iron complexes 103 are converted by activated acetylenes into air-sensitive carbene complexes 104. Decomposition of the latter in air provides an unusual synthetic route to substituted tetrathiofulvene derivatives (Scheme 121).187... 

The obtained obs values are reported as a fimction of the complex concentration (Fig. 8), and a good linear correlation between obs and the complex concentration was observed for both oxidation forms of iron complexes. From the slope of the plot of obs vs. catalyst concentration the catalytic rate constants ( cat) i29) were determined to be (3.7 0.5) X 10 M- s and (3.9 0.5) x 10 M s for [Fe (dapsox)(-H20)2]C104 and [Fe (H2dapsox)(H20)2](NOs)2, respectively 49). It is important to note that, it does not matter whether we start from the Fe(III) or Fe(II) form of the complex, identical spectral changes (Fig. 6a and 6b) and kinetic behavior (Fig. 8) for these two complexes is observed upon reaction with, which is consistent with the redox cychng of the complex during O2 decomposition (Scheme 9). 

It is essential to characterize the reactant species in solution. One of the problems, for example, in interpreting the rate law for oxidation by Ce(IV) or Co(III) arises from the difficulties in characterizing these species in aqueous solution, particularly the extent of formation of hydroxy or polymeric species. We used the catalyzed decomposition of HjOj by an Fe(III) macrocycle as an example of the initial rate approach (Sec. 1.2.1). With certain conditions, the iron complex dimerizes and this would have to be allowed for, since it transpires that the dimer is catalytically inactive. In a different approach, the problems of limited solubility, dimerization and aging of iron(III) and (Il)-hemin in aqueous solution can be avoided by intercalating the porphyrin in a micelle. Kinetic study is then eased. 

Thus, antioxidant effects of nitrite in cured meats appear to be due to the formation of NO. Kanner et al. (1991) also demonstrated antioxidant effects of NO in systems where reactive hydroxyl radicals ( OH) are produced by the iron-catalyzed decomposition of hydrogen peroxide (Fenton reaction). Hydroxyl radical formation was measured as the rate of benzoate hydtoxylation to salicylic acid. Benzoate hydtoxylation catalyzed by cysteine-Fe +, ascorbate - EDTA-Fe, or Fe was significantly decreased by flushing of the reaction mixture with NO. They proposed that NO liganded to ferrous complexes reacted with H2O2 to form nitrous acid, hydroxyl ion, and ferric iron complexes, preventing generation of hydroxyl radicals. 

Co-oxidation of indene and thiophenol in benzene solution is a free-radical chain reaction involving a three-step propagation cycle. Autocatalysis is associated with decomposition of the primary hydroperoxide product, but the system exhibits extreme sensitivity to catalysis by impurities, particularly iron. The powerful catalytic activity of N,N -di-sec-butyl-p-phenylenediamine is attributed on ESR evidence to the production of radicals, probably >NO-, and replacement of the three-step propagation by a faster four-step cycle involving R-, RCV, >NO, and RS- radicals. Added iron complexes produce various effects depending on their composition. Some cause a fast initial reaction followed by a strong retardation, then re-acceleration and final decay as reactants are consumed. Kinetic schemes that demonstrate this behavior but are not entirely satisfactory in detail are discussed. 

The products of co-oxidation examined after oxygen absorption has ceased and after the hydroperoxide had rearranged were substantially the same as those obtained in absence of added iron, although some changes in the yields of minor products resulted from the effects of the iron complexes on the decomposition of the hydroperoxide. 

The other example to be discussed in this context comes from Pettit s group. Simultaneous treatment of the iron complex (/u.-CH2)[Fe(CO)4]2 (35) with hydrogen and ethylene gives both methane (66%) and propylene (6%), the expected products from the two separate reactions. In addition, ethane (—600%) is formed, with the actual hydrogenation catalyst still to be determined (72). Because simple diazoalkanes provide the cleanest method to metal-attached alkylidenes, and with the expectation that dissociative chemisorption of diazomethane to absorbed CH2 and free N2 would occur, the reactions of CH2N2 with and without H2 over various transition metals were examined in a careful study with regard to the product ratio (73). It was found, that gas-phase decomposition of the parent diazoalkane upon passage over active Ni, Pd, Fe, Co, Ru, or Cu-... 

The iron compound readily sublimes and yields well-formed, black lustrous crystals. The cobalt complex will also readily sublime, but dependent upon the temperature at which the crystals are formed, they can be either black or brown in color. The crystal structures of both the cobalt and iron complexes have been determined.3 The nickel complex sublimes only in small amounts with difficulty. All three complexes are unstable to air and water, and the nickel complex readily undergoes thermal decomposition above 100°C. All three compounds will also readily form complexes with a variety of donor ligands such as tertiary arsines or phosphines. The nickel compound usually forms 2 1 adducts such as [(C6HS )3P]2Ni(NO)I, while the iron and cobalt complexes often undergo disproportionation.5... 

The first reports on iron-catalyzed aziridinations date back to 1984, when Mansuy et al. reported that iron and manganese porphyrin catalysts were able to transfer a nitrene moiety on to alkenes [90]. They used iminoiodinanes PhIN=R (R = tosyl) as the nitrene source. However, yields remained low (up to 55% for styrene aziridination). It was suggested that the active intermediate formed during the reaction was an Fev=NTs complex and that this complex would transfer the NTs moiety to the alkene [91-93]. However, the catalytic performance was hampered by the rapid iron-catalyzed decomposition of PhI=NTs into iodobenzene and sulfonamide. Other reports on aziridination reactions with iron porphyrins or corroles and nitrene sources such as bromamine-T or chloramine-T have been published [94], An asymmetric variant was presented by Marchon and coworkers [95]. Biomimetic systems such as those mentioned above will be dealt with elsewhere. 

Reactions of complexes of 1,2-cycloheptadienes have received only cursory attention. 1,2-cycloheptadiene is readily displaced from bisftriphenyl-phosphine)platinum(O)118 [Eq. (54)], but no reagent has been found that will displace the allene from iron.119 Reaction of the iron complex with alcohol in the presence of base (e.g., 312 — 322) is typical of Fp+ complexes of acyclic allenes.131132 The thermal chemistry of 312 is unusual in its decomposition to 324 (Scheme 41). This is probably attributable to the presence of the triflate counterion, since the corresponding fluoroborate salt is stable when warmed to 40°C for 16 h.119 A mechanism to 324 via carbene complex 321 appears likely. 

First, 240 ml. of air-free water is placed in a 1-1. nitrogen-filled three-necked flask equipped with a stirrer and a reflux condenser. Then, 110 ml. (160 g. 0.82 mol) of iron pentacarbonyl and 83 ml. (60 g. 0.59 mol) of triethylamine are added, and the mixture is stirred and heated at 80° under nitrogen for 10 hours or overnight, whichever is more convenient. It is important that the proper temperature be maintained, because below 75° the reaction is incomplete and above 90° decomposition of the iron complex occurs. 

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