Superoxo cobalt complex

Figure 26.2 O2 bridges in dinuclear cobalt complexes (a) peroxo (02 ) bridge, and (b) superoxo (02 ) bridge.

Table 53 gives a list of a number of cobalt(III)-superoxo complexes which have been isolated as crystalline solids. There is a marked preponderance of complexes of the type [Co(SB)(B)(02)] (SB = SchifF base). The base adducts of simple Co11 porphyrins have low affinities for dioxygen at room temperature and consequently their 1 1 adducts with 02 are not isolable. In contrast, exposure of a solid sample of Collman s picket fence porphyrin system [Co(TpivPP)(iV-Meim)] to 1 atm of dioxygen for 24 h produces [Co(TpivPP)(A(-Meim)(02)] (200).654 The pivalamido pickets in this compound exercise control of solvation about the coordinated dioxygen moiety and the stability is comparable with that of CoMb02,655 where the globin protein environment performs the same function. 

Table 53 Crystalline Monomeric Cobalt(III)-Superoxo Complexes...

Apart from the unambiguous and useful classification of the dinuclear cobalt complexes as /i-peroxo or /i-superoxo species, we shall not use formal oxidation states frequently in this review, and we limit the discussion here to the following points ... 

Hydroperoxo complexes can also be obtained by a one-electron reduction of the superoxo intermediates [Ru(NH3)6]2 + is one of the most convenient reducing agents for this chemistry.15 An interesting way of preparing hydroperoxides via dioxygen activation utilizes a formal 02 insertion into M-H bond in metal hydrides examples are known for platinum, rhodium, and cobalt complexes, to name just a few.14,15... 

Figure 6. EPR spectra of oxygen-containing samples of [sCImCo(II)]2 diporphyrins. (A) Upper trace complex of 1 with 1 atm of O2 at 77° K bottom trace after sample was evacuated at --20°C and recorded at 77°K. (B) Room temperature spectrum of the dioxygen adduct of cobalt complex of 3 after addition of small amount of I2. This is a typical binuclear fx-superoxo dicobalt spectrum. All experiments were carried out in CH2CI2/toluene mixtures.

The T) t) dinuclear complexes may be of the /Li-peroxo or p-superoxo type [26], and are very widespread among cobalt complexes. ESR evidence indicates that the unpaired electron is localized on the dioxygen moiety in the superoxo species [165]. The 0-0 bond distances are close to those observed in free peroxide and superoxide. 

These 5-coordinate cobalt complexes form mononuclear superoxo and bridged dinuclear -peioxo complexes, which are reactive toward phenolic substrates, thereby initiating catalytic oxidation cycles ... 

Dioxygen binding to cobalt complexes is well known and has been reviewed extensively [74]. The most widely studied systems are cobalt porphyrin and salen complexes [salen, N,N -bis(salicylidene)-l,2-ethylene-diaminato(2-)], with the latter dating back to the time of Werner [75]. The reactions of these systems most often involve Co(II) complexes and the formation of stable cobalt-(// -superoxo) complexes or species with Co(III)(/t-l,2-peroxo)Co(III) cores. Recent work has focused on more reactive cobalt-dioxygen species and will be highlighted here. 

Figure 14.5 (a) Reaction of Al,Al -ethylenebis(3-Bu -salicylideniminato)cobalt(II) with dioxygen and pyridine to form the superoxo complex [Co(3-Bu Salen)2(02)py] the py ligand is almost coplanar with the Co-O-O plane, the angle between the two being 18°.< (b) Reversible formation of the peroxo complex [Ir(C0)Cl(02)(PPh3)2]. The more densely shaded part of the complex is accurately coplanar. ... 

Barraclough CG, Eawrance GA, Fay PA. 1978. Characterization of binuclear /r-peroxo and /Li-superoxo cobalt(III) amine complexes from Raman spectroscopy. Inorg Chem 17 3317. 

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