Terminal dioxygen

Iron(II) complex of tris(N -tert-butylurea-ylato)-N-ethylene]aminato activates dioxygen at room temperature to afford an iron(III) complex containing a single terminal oxo ligand. X-ray structures show that the three urea molecules act as a tridentate N,N,N-hgand [52]. The tripodal ligand was also used to synthesise complexes of cobalt, iron or zinc with terminal hydroxo ligands (Scheme 8) [53]. 

Collman JP, Boulatov R, Sunderland CJ. 2003a. Functional and structural analogs of the dioxygen reduction site in terminal oxidases. In Kadish KM, Smith KM, Guilard R, editors. The Porphyrin Handbook. Boston Academic Press, p. 1. 

It should be clear from Section IV. B that a major difficulty involved in preparing monomeric iron-dioxygen adducts is the prevention of bimolecular termination reactions, leading via autoxidation to the formation of a ju-oxo dimer, thus... 

We saw previously that a major factor in inhibiting the bimolecular termination reaction was the presence of sufficiently bulky ligands so that a monomeric dioxygen adduct could be isolated 135). A number of synthetic metal porphyrins 239) have been prepared recently which satisfy the above requirement, and bind molecular oxygen we shall now proceed to discuss these. 

During the course of modeling copper dioxygen chemistry, Kitajima et al. reported the synthesis of a yu-peroxo dinuclear complex with a 3,5-dimethyl-substituted tris(pyrazolyl)borate ligand, which showed remarkable physicochemical similarities to oxy-Hc and oxy-Tyr. Using a 3,5-di-isopropyl-substituted terminal ligand, they provided the first structural proof of the existence of peroxo dicopper(II) core (108) (copper geometry distorted square pyrami-... 

If the partial pressure of dioxygen varies greatly, reactions (tl) and (t2) contribute considerably to chain termination at low concentration of dioxygen. So, in the general case,... 

The formed methyl radical adds dioxygen, and the methylperoxyl radical participates in chain termination ... 

The formed alkyl radical reacts with dioxygen in the oxidized hydrocarbon. Participating in chain termination, the newly formed peroxyl radical accelerates it ... 

Scheme A. This scheme is typical of the hydrocarbons, which are oxidized with the production of secondary hydroperoxides (nonbranched paraffins, cycloparaffins, alkylaro-matic hydrocarbons of the PhCH2R type) [3,146]. Hydroperoxide initiates free radicals by the reaction with RH and is decomposed by reactions with peroxyl and alkoxyl radicals. The rate of initiation by the reaction of hydrocarbon with dioxygen is negligible. Chains are terminated by the reaction of two peroxyl radicals. The rates of chain initiation by the reactions of hydroperoxide with other products are very low (for simplicity). The rate of hydroperoxide accumulation during hydrocarbon oxidation should be equal to ...

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