Activation of dioxygen

Selective controlled oxidations using dioxygen are difficult to achieve but are industrially very important. The basic mechanisms of homogeneous catalytic oxidation reactions are discussed in Chapter 8. Here we discuss the modes of interaction of dioxygen and dioxygen-derived ligands with metal. 

Before picking up 0, the Fe + is coordinated to five nitrogen atoms, four from a planar porphyrin ligand and the fifth from an imidazole of a histidine. Note that porphyrin is a dianionic planar ligand that coordinates to the metal, through the nitrogen atoms of four pyrrole rings. 

The vanadium complex 2.73 has a peroxo ligand. An analogue with an alkylperoxo (RO ) ligand that has a similar strucmre is also known. The oxidation state of vanadium in 2.73 is 5+. As we will see later, the alkyl peroxo analogue of 2.73 is a model (see Section 3.4) that mimics the mode of activation of organic hydroperoxides by high-valent metal ions. 

Finally, it must be noted that conversions of dioxygen to oxo ligands by iron- and copper-containing metalloenzymes are well established. The basic reactions of relevance observed in the iron-containing CytT are shown by reaction 2.3.7.1. 

the ligand environment of iron provided by the protein is similar to that of 2.71. The final oxo complex can oxidize many hydrocarbons to their corresponding hydroxo derivatives (see Section 8.5), and alkenes to epoxides. 

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T.G. Spiro (ed.). Metal Ion Activation of Dioxygen, Wiley-Interscience, New York, 1980, 247 pp. 

Activation of Dioxygen by Cobalt Group Metal Complexes Claudio Bianchini and Robert W. Zoellner... 

Simandi LI (2003) Advances in catalytic activation of dioxygen by metal complexes. Kluwer, Dordrecht... 

The oxidation of phenol, ortho/meta cresols and tyrosine with Oj over copper acetate-based catalysts at 298 K is shown in Table 3 [7]. In all the cases, the main product was the ortho hydroxylated diphenol product (and the corresponding orthoquinones). Again, the catalytic efficiency (turnover numbers) of the copper atoms are higher in the encapsulated state compared to that in the "neat" copper acetate. From a linear correlation observed [7] between the concentration of the copper acetate dimers in the molecular sieves (from ESR spectroscopic data) and the conversion of various phenols (Fig. 5), we had postulated [8] that dimeric copper atoms are the active sites in the activation of dioxygen in zeolite catalysts containing encapsulated copper acetate complexes. The high substratespecificity (for mono-... 

Bianchini C, Zoellner RW. 1997. Activation of dioxygen by cobalt group metal complexes. Advinorg Chem 44 263. 

ELECTROCATALYTIC REDUCTION AND ACTIVATION OF DIOXYGEN 9.10.7.1 Electrocatalytic Four-electron Reduction of Dioxygen... 

L.I. Simandi (ed.) Catalytic Activation of Dioxygen by Metal Complexes. 1992... 

The activation of dioxygen by the nickel complex and the generation of radicals by the reaction of the Ni(II).02 complex with ethylbenzene were proposed. Examples of reactions... 

In addition to hydroperoxide decomposition, the copper surface was found to initiate the chains through activation of dioxygen. The rate of chain initiation in the presence of the copper powder was found to be... 

Reviews on the activation of dioxygen by transition-metal complexes have appeared recently 9497 ). Details of the underlying reaction mechanisms could in some cases be resolved from kinetic studies employing rapid-scan and low-temperature kinetic techniques in order to detect possible reaction intermediates and to analyze complex reaction sequences. In many cases, however, detailed mechanistic insight was not available, and high-pressure experiments coupled to the construction of volume profiles were performed in efforts to fulfill this need. 

One of the most fundamental questions when dealing with the activation of dioxygen by transition metal complexes is whether the process is controlled kinetically by ligand substitution or by electron transfer. A model system that involved the binding of dioxygen to a macrocyclic hexamethylcyclam Co(II) complex to form the correspond-... 

The binding of CO has in many studies been used as a model for the activation of dioxygen, since this molecule does not undergo any real activation in the systems studied it merely binds to the metal center. The absence of subsequent electron transfer reactions simplifies the kinetic analysis and reveals more mechanistic insight on the actual binding process. 

Ezhova, M. B. James, B. R. in Advances in Catalytic Activation of Dioxygen by Metal Complexes , Ed. Simandi, L. S. Volume 26, Catalysis by Metal Complexes, Kluwer Academic Publishers, Dordrecht, 2003. 

R. Raja, and R. Ratnasamy, Activation of dioxygen by copper complexes incorporated in molecular sieves, J. Mol. Catal. A 100, 93-102 (1995). 

Lien, H.-L. and Wilkin, R. Reductive activation of dioxygen for degradation of methyl ferf-butyl ether by bifunctional aluminum. Environ. Sci. Technol, 36(20) 4436-4440, 2002. 

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