Dioxygen iron catalysts

Usually, a large excess of the reducing agent(s) is necessary. Representative examples are (1) porphyrin systems metalloporphyrin or metallophthalocyanin -I- reductant (H2, NaBH4, etc) -I- O2 and (2) Gif systems iron catalyst -I- reductant (eg, Zn) -)- O2. Another example is to combine dioxygen and aldehyde, which has recently attracted attention as an effective oxidizing system when combined with various metal complexes (eq. (13)) (23). 

Other aspects of solvation have included the use of surfactants (SDS, CTAB, Triton X-100), sometimes in pyridine-containing solution, to solubilize and de-aggregate hemes, i.e., to dissolve them in water (see porphyrin complexes, Section 5.4.3.7.2). An example is provided by the solubilization of an iron-copper diporphyrin to permit a study of its reactions with dioxygen and with carbon monoxide in an aqueous environment. Iron complexes have provided the lipophilic and hydrophilic components in the bifunctional phase transfer catalysts [Fe(diimine)2Cl2]Cl and [EtsBzNJpeCU], respectively. 

In 1990, Triantaphylidds and coworkers reported on the preparative enzymatic synthesis of hnoleic acid (135) hydroperoxide 24a using soybean lipoxygenase-1. In this dioxygenation asymmetry is induced by the catalyst, the enzyme. The reaction was later used by Dussault and also by Baba and coworkers as key step in the preparation of more complex peroxides. The enzyme is a non-heme iron dioxygenase which catalyzes the incorporation of dioxygen into polyunsaturated fatty acids to yield E,Z conjugated diene hydroperoxides 24a-d. With this enzymatic method, the hydroperoxide 24a could... 

The reduced iron atoms of complex C, being inert to dioxygen, are readily oxidized by nitrous oxide into complex D to give adsorbed species of a-oxygen, Oa. As Figure 7.3 shows, the reversible redox transition Fc" <-> Fe provides the catalytic activity of FeZSM-5 both the oxidation cycle due to the oxygen transfer from N20 to a substrate and the decomposition cycle of N20 into N2 and 02 due to recombination of a-oxygen into the gas phase. The decomposition is an environmentally important process, and FeZSM-5 zeolites are considered to be the best catalysts for this reaction (see review [117] and references therein). 

The unique versatility of ruthenium as an oxidation catalyst continues to provide a stimulus for research on a variety of oxidative transformations. Its juxtaposition in the periodic table and close similarity to the biological redox elements, iron and manganese, coupled with the accessibility of various high-valent oxo species by reaction of lower-valent complexes with dioxygen make ruthenium an ideal candidate for suprabiotic catalysis. 

Although the decomposition of ozone to dioxygen is a thermodynamically favoured process,126 it is thermally stable up to 523 K and catalysts are needed to decompose it at ambient temperature in ventilation systems, in the presence of water vapour and at high space velocity. A limited number of catalysts have been evaluated and active components are mainly metals such as platinum, palladium and rhodium, and metal oxides including those of manganese, cobalt, copper, iron, nickel and silver. Supports that have been used include 7-alumina, silica, zirconia, titania and activated carbon.125,170... 

Fe20(0Ac)2Cl2(bipy)2 successfully hydroxylates C6, C3, and C2 alkanes when tert-butyl hydrogen peroxide (TBHP) is used as the oxygen donor ([5] [TBHP]-.[substrate] = 1 150 1100) the observed reactivity is C6 > C3 > C2 (Table IV). This work represents the first report of the oxidation of a small molecular weight alkane (ethane) by a characterized iron model compound. Reactions of this complex with Zn dust and acetic acid under 1 atm of dioxygen with cyclohexane gave rise to only cyclohexanone (turnover number 2.5). The parent tetrameric compound, 6, was reported to be a more efficient catalyst. 

The [TPPFeCl] -NaBITi system in diglyme has been shown to perform remarkably efficiently as a catalyst for the reduction of nitrobenzenes to anilines. Although both TPPCo and TPPMnCl also catalyze the reduction of p-chloronitrobenzene to jo-chloroaniline, their catalytic activities are much lower thanthatofTPPFeCl. Anothertype of reduction catalyst, in this case of dioxygen to water, begins with carbon-supported chloroiron(ni) tetramethoxyphenylporphyrin, which is then heat-treated at 900 °C for one h." This causes decomposition of the porphyrin to produce metallic, carbidic and oxidic iron, as detected by Mossbauer spectroscopy. The active... 

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