Oxidation chromium-peroxo complexes

Oxygen reacts readUy with /ns(di-isopropylaminato)chromium(III). Cold pentane solutions yield [Cr(02XNPr2)3] while under different conditions ESR evidence has been found for a chromium(IV) complex of di-isopropylnitroxide, [CrO(NPr2)2(ONPr 2)] [66]. The chromium peroxo complex VI, selectively oxidizes tetraphenylcyclopentadienone, however, some disagreement exists concerning the nature of the organic product obtained [93,94]. 

Like other transition metals, notably Ti, V, Nb, Ta, Mo, and W, chromium forms peroxo compounds in the higher oxidation states. Most of them are unstable, and in the solid state some of them are dangerously explosive or flammable in air. Bis(peroxo)chromium(IV) complexes with nitrogen ligands are remarkably stable, e.g., (17-C-XII).40... 

The peroxo-complexes provide further examples of the ability of oxygen to coordinate to the metals in their high oxidation states. The production of blue solutions when acidified dichromates are treated with H2O2 is a qualitative test for chromium. The colour arises from the unstable CrO. which can, however, be stabilized by extraction into ether, and blue solid adducts such as tCrOs(py)] can be isolated. This is more correctly formulated as lCr0(02>2py] and has an approximately pentagonal pyramidal structure (Fig. 23.6a). Bidenlate ligands, such as phenanlhroline and bipyridyl produce pentagonal bipyramidal complexes in which the second N-donor atom is loosely bonded irons to the =0 (Fig. 23.6b). This 7-coordinate structure is favoured in numerous peroxo-complexes of Mo and W, and the dark-red peroxo anion [Mo(02)4] is 8-coordinate, with Mo-O 197 pm and 0-0 155 pm. 

Wood RM, Abboud KA, Palenik GJ (2000) Bond valence sums in coordination chemistry. Cedculation of the oxidation state of chromium in complexes containing only CiM3 bonds and a redetermination of the crysUil structure of potassium tetra(peroxo)chromate (V). Inorg Chem 39 2065-2068... 

Alkoxo monoperoxo vanadium complexes are also efficient radical oxidants of the alcoholic function164-166 167 again with a radical chain mechanism whose details are indicated in Scheme 16 in the case of 2-propanol. Similar radical peroxo species have been indicated as competent oxidant also in the oxidation of alcohols with bis-peroxo chromium complexes159. 

III.B.2), complexes with manganese, chromium, as well as second- and third-row transition metal ions (e.g., ruthenium) oxidation reactions with dioxygen alone or with other peroxides (e.g., ferf-butyl-peroxide) the stabilization and spectroscopic characterization of mononuclear superoxo, peroxo, and oxo complexes other catalytic processes (e.g., the iron-catalyzed aziridination), enantioselective reactions with chiral bispidine ligands and the iron oxidation chemistry continues to produce novel and exciting results. 

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