Porphyrins oxygenated cobalt

ESR studies also show the similarity between oxycoboglobin and oxygenated cobalt porphyrin, and suggest that the protein does not measurably influence the electronic structure of the heme group, although the protein does control the extent to which dioxygen is bound. 

Figure 8 Oxygen permeability coefficient Po.) and oxygen/nitrogen selectivity (insert) for the liquid membrane of cobalt-porphyrin. The cobalt-porphyrin concentration in the membrane 31% at — 5°C (circle), the control membrane containing inert Co(III) derivative (square).

Gadamsetti K, Swavey S. 2006. Electrocatalytic reduction of oxygen at electrodes coated with a bimetallic cobalt(II)/platinum(II) porphyrin. J Chem Soc Dalton Trans 5530. 

It has been noted (2) that many oxygen-carrying cobalt(II) complexes involve ligands that provide four donor atoms lying in the same plane as the cobalt atoms, such as salen , porphyrin and dimethylglyoxime, DMG, and related ligands. 

Sugamoto and colleagnes have attempted the rednction-nitrosation of the conjn-gated olefins 33 by the nse of f-bntyl nitrite instead of oxygen (Scheme 24). Various olefins such as styrenes, a,-unsaturated carbonyl compounds and a, S,y,5-unsaturated carbonyl compounds were directly converted to the corresponding acetophenone oximes, a-hydroxyimino carbonyl compounds and y-hydroxyimino-a,/S-unsaturated carbonyl compounds in good or moderate yields by rednction-nitrosation with f-butyl nitrite and triethylsilane in the presence of cobalt(II) porphyrin as a catalyst (Scheme 24). 

Transition metal compounds, such as organic macrocycles, are known to be good electrocatalysts for oxygen reduction. Furthermore, they are inactive for alcohol oxidation. Different phthalocyanines and porphyrins of iron and cobalt were thus dispersed in an electron-conducting polymer (polyaniline, polypyrrole) acting as a conducting matrix, either in the form of a tetrasulfonated counter anion or linked to... 

Cobalt porphyrins have been some of the most studied catalysts for oxygen reduction, due in part to their strong interaction with molecular oxygen and the ease with which they catalyze the reduction at low potentials. Anson and coworkers [97] performed a study of the simplest of cobalt porphyrins, cobalt porphine, in the hope of gaining a baseline for the observed reactions of other porphyrins. Instead, they observed a very different process from most other monomeric cobalt porphyrins. 

Substituted cobalt porphyrins as catalysts in sulfuric acid. Further very active chelates for the reduction of oxygen in acids discovered in the early 70s were CoTPP by Sandstede and co-workers 9,13-15) and CoTAA and FeACC by Beck and co-workers 8 12>. Sandstede et al. determined the activities of their chelate catalysts by the suspension method briefly explained in Section 2.2.2.3. 

A picnic-basket porphyrin is reminiscent of the lacunar cyclidenes mentioned earlier, in which an alkyl chain tied the ends of the cyclidene together and formed a pocket for the complexation of dioxygen. Cobalt complexes of the picnic-basket porphyrins 31 bind dioxygen reversibly at room temperature with high oxygen affinities (84). The oxygen affinity increases as the basket size decreases (as determined by the length... 

A Co(II) Schiff-base complex converts 1- and 2-alkenes into methyl ketones and the corresponding secondary alcohols in the presence of oxygen or H2O2 in primary alcohol solvent.543 A radical oxidation with cobalt hydroperoxide through the formation and subsequent decomposition of alkyl hydroperoxide was suggested.543 An efficient conversion of alkenylarenes to ketones was achieved by the use of molecular oxygen and EtjSiH in the presence of a catalytic amount of Co(II) porphyrin in 2-propanol.544... 

Cobalt(II) porphyrins bind dioxygen as would be expected by analogy with the wealth of cobalt(II) complexes which display this property. The initial addition product is invariably a superoxo-type species, confirmed by ESR, IR and X-ray studies.154 Subsequent reaction of the oxygenated complex with more Co11 porphyrin leads to a peroxo-bridged dimer. No X-ray data are available for cobalt porphyrin peroxo-bridged dimers but the formation of such dimers is well established in cobalt chemistry. 

Cobaltn-Schiff base complexes, e.g. Co(salen),567 Co(acacen)568 and cobalt(II) porphyrins,569 e.g. Co(TPP), are effective catalysts for the selective oxygenation of 3-substituted indoles to keto amides (equation 249), a reaction which can be considered as a model for the heme-containing enzyme tryptophan-2,3-dioxygenase (equation 21).66 This reaction has been shown to proceed via a ternary complex, Co-02-indole, with probable structure (175), which is converted into indolenyl hydroperoxide (176). Decomposition of (176) to the keto amide (174) readily occurs in the presence of Co(TPP), presumably via formation of a dioxetane intermediate (177).569,56 Catalytic oxygenolysis of flavonols readily occurs in the presence of Co(salen) and involves a loss of one mole of CO (equation 251).570... 

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