Cobalt complexes peroxy

The reversible formation of a low-spin [Co (III) (NHS) n02 ]2+ complex within a Co (II) Y zeolite has been demonstrated by EPR spectroscopy. In this complex n is probably equal to five. A maximum of one cobalt complex per large cavity was farmed. The cobalt hyperfine structure shows that the unpaired electron is only 8% on the metal ion. Experiments utilizing 170 indicate that 02 enters the coordination sphere of the Co2+ ions and that the unpaired electron is largely associated with the oxygen molecule. The oxygen-17 hyperfine structure reveals that the two oxygen atoms are not equivalent hence, it is concluded that the oxygen is bonded as a peroxy-type superoxide ion. 

On the basis of these observations and conclusions it was suggested that the cobalt complexes described above might follow a related pathway. Here, however, it can be argued that the presence of base in, e.g. the reactions of Co(dmgH)2NO, leads initially to the quantitative formation of Co,(dmgH)2(NO)B. In this case attack of 02 leads first to the peroxy compounds and then, because of the absence of a suitable NO+ compound, rearrangement occurs to give the nitrito derivative. Clearly whether or not nitro or nitrato compounds are produced would depend on the concentration of base B. In some cases it is possible to obtain mixtures of such products. These oxidations are also observed for other metals, e.g. equations (37) and (38). 

When the Co(bpb)H20 complex 234 was used in MeCN under an oxygen atmosphere (room temp., 4 h), 2,6-di(terr-butyl)-4-methylphenol (69) was converted into a peroxy-p-quinalato-cobalt complex 246, as a sole product (47%), suggesting that 246 supports the intermediacy of Co(L)-00 in the reaction (Scheme 51) °. ... 

In connection with hgnan chemistry, oxygenation of syringyl alcohol (247) with O2 in the presence of 10% of the 5-coordinate catalyst 231 or 229-pyridine complex afforded 2,6-dimethoxy-p-benzoquinone (248) in 71 and 88% yields, respectively (Scheme 52). A peroxy-p-quinalato-cobalt complex 249 is a plausible intermediate in the oxidation . ... 

It is proposed that the reaction takes place via a cobalt(in)-peroxy species which reacts with the alkanes to form cobalt(II)-alkylhydroperoxide complexes. These complexes decompose to form preferentially ketones, with concomitant regeneration of cobalt(II) acetate . ... 

We have initiated a study of the photoreduction of a series of paramagnetic peroxy-bridged dicobalt ammines. All of these complexes, which are shown below, contain the (Co-O-O-Co)5 + group, which best present evidence indicates should be represented as (Co -O-O-Com)5+, although ESR studies indicate that the extra electron is to some extent delocalized over the cobalt centers.78,79,82 Our idea was derived from Sykes report in 196363 that solutions of l-p in sunlight in dilute acid were decomposed according to the stoichiometry shown in reaction (29). 

It has been shown that mononuclear cobalt superoxo complexes react with 2,4,6-tri-t-butyl-phenol. The anion [Co(CN)5(02)]3 acts as a base in the oxidation of the phenol. The neutral complex Co(salptr)(Oz) forms a peroxy adduct with 2,4,6-tri-t-butylphenol. An X-ray study on this adduct has revealed the structure shown in (10).m... 

In another interesting amplification system, an image in silver or other noble metal nuclei is used for catalysis, and a cobalt(III) complex is used as an oxidant in place of a peroxy compound. The amplification permits less silver to be used. An imagewise distribution of silver nuclei is associated with a non-diffusible dye-forming coupler, and the image is amplified by (1) imbibing the system with a solution containing a color developer such as a p-phenylenediamine and (2)... 

Transition metal ions (Co, in particular) catalyze decomposition of ROOH with formation of alkoxy and peroxy radicals, as shown in reactions (4.10) and (4.11) [11, 12]. We would like to note here that the decomposition of hydroperoxides and peracids on cobalt(II) and (III) is more complex than what are shown in Eqs. (4.10) and (4.11) and involves several steps and two equivalents of Co(II) [16, 17, 18a, 19]. 

Then, the effects of ligands of cobalt(II) complexes in the above reaction was examined and was found that various bis(l,3-diketonato)cobalt(II), especially Co(modp)2, were effectively employed as catalysts. Preparation of a peroxy compound directly from olefin has been considered to be difficult because of its unstability. The present peroxygenation reaction, however, provides a facile and efficient method for the direct introduction of dioxygen function into the carbon-carbon double bond of olefmic compounds under mild conditions (Table 4). In addition, the triethylsilyldioxy derivative here is expected to be a potentially useful synthetic intermediates. 

Apparently, these peroxy-cobalt species are involved as intermediates in the catalytic oxygenation of 1. Indeed in the initial stages of that reaction in MeOH at room temperature only the peroxy complex 17 and p-quinol 15 can be detected. The conversion of 17 to the p-quinol occurs via hydroperoxide 20 formed by solvolysis with MeOH ... 

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