Peroxo-cobaltic

CoCl(PPh3)3], Reaction of [Co(TIMEN )]Cl 9 with oxygen in the presence of NaBPh leads to the formation of the peroxo-complex [Co(r -02)(TIMEN 5 )] BPh 10, which is a rare example of a side-on r -peroxo cobalt complex (the majority of Co-O -adducts are rj -O -complexes, i.e. end-on). The authors also showed that 10 is capable of converting molecular oxygen to benzoylchloride. 

Reduction potentials for /z-superoxo//z-peroxo-cobalt(III) couples have recently been obtained by cyclic voltammetry.739,740 Decomposition or dissociation of one or the other of the components of the couple, which frustrated measurements by other techniques, may be overcome by the use of fast scan rates. Protonation of the /r-peroxo group stabilizes the complex and EB values are pH dependent below pH 3. A similar stabilization on protonation of the peroxo bridge has been noted in the Ct2+-, V2+- and Eu2+-promoted reduction705 of the [(NHj)5Co(02)Co(NH3)5]4+ ion. The protonated species has Kh 10 dm3 mol-1 at 25 °C.705... 

However, the similarity in bond strengths of the peroxide linkage to molecular 02, the ease with which the known -peroxo Cobalt complexes liberate 02 (in contrast to /x-oxo bipyridyl Mn dimers) on photolysis, kinetic barriers on ju-oxo to peroxo dimer conversions led Sawyer et al.47 -49) to suggest peroxo binuclear complexes as the most probable intermediates. More studies with model compounds are needed to elucidate this point. Various mechanisms proposed for water oxidations are variations of these two principal types. 

Selected structural data for /i-peroxo cobalt(III) complexes are included in Table 57. Orbital diagrams constructed for Co—O—O bonds in N4Co(02)CoN4 species show that irons bent bonds are the most stable and this is what is observed for the monobridged complexes. Dibridging forces the /i-peroxo group to adopt a skewed cis geometry except in cases (e.g. [(tren)Co(/i-tren,02)Co-... 

Oxygen adducts are readily formed by the air bubbling of a solution of cobalt amine complex. Similar p-peroxo cobalt(III) complexes are formed by the reaction of oxygen with a variety of cobalt(II) chelates. The amine ligands in oxygen-binding complexes also have been extended to polyamines, such as poly(ethyleneimine) (details are given in Experiment 9-4, Section 9.5). 

A number of short reviews have appeared in addition to those already mentioned. They deal with the reactivity of dinuclem jM-peroxo-cobalt(in) chelates and rhodium cyanides, with metal and ligand isotopic exchange reactions of chelate complexes, and the applications of isotopes to kinetic studies of carbonate systems. A new book deals with the diverse applications of n.m.r. for kinetic studies in solution, including a chapter devoted to st -eochemically non-rigid metsd chelate complexes. In a further review the dynamics of intramolecular metal-centred rearrangement reactiom of fris-chelate complexes is described. ... 

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