Peroxo complex

The colour sequence already described, for the reduction of van-adium(V) to vanadium(II) by zinc and acid, gives a very characteristic test for vanadium. Addition of a few drops of hydrogen peroxide to a vanadate V) gives a red colour (formation of a peroxo-complex) (cf. titanium, which gives an orange-yellow colour). 

Peroxidic Compounds. When hydrogen peroxide is added to a solution of titanium(IV) compounds, an intense, stable, yellow solution is obtained, which forms the basis of a sensitive method for determining small amounts of titanium. The color probably results from the peroxo complex [Ti(02)(0H)(H20)J, and crystalline salts such as K2[Ti(02)(S0 2] H20 can be isolated from alkaline solutions. The peroxo ligand is bidentate the two oxygen atoms ate equidistant from the titanium (98). 

Aminechromium peroxo-complexes Azides (acyl, halogen, non-metal, organic) Arenediazoniumolates... 

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. ... 

Figure 14.8 Schematic representation of the planar central portion of the /r-peroxo complex [La N(SiMe3)2)2(OPPh3)]202.

One of the most sensitive methods for estimating titanium (or, conversely, for estimating H2O2) is to measure the intensity of the orange colour produced when H2O2 is added to acidic solutions of titanium(IV). The colour is due > to the peroxo complex, [Ti(02)(0H)(H20)jt]", though alkaline solutions are needed before crystalline solids such as M3[Ti(02)Fs] or M2[Ti(02)(S04)2]... 

If X-Y bond fission occurs, the product is a 6-coordinate iridium(III) complex (Table 2.6) otherwise a 5-coordinate (or pseudo-5-coordinate) adduct is obtained in which Ir formally retains the (+1) state (Table 2.7). This distinction can be somewhat artificial IrCl(02)C0(PPh3)2 can be regarded as an iridium(III) peroxo complex. 

Similarly, when both the Cp and arene ligands are permethylated, the reaction of 02 with the Fe1 complex leads to C-H activation of the more acidic benzyl bond [57]. When no benzylic hydrogen is present, superoxide reacts as a nucleophile and adds onto the benzene ligand of the FeCp(arene)+ cation to give a peroxocyclohexadienyl radical which couples with a Fe Cp(arene) radical. A symmetrical bridging peroxo complex [(Fe"Cp)2(r 5-C6H60)2] is obtained. The C-H activation reactions of the 19e Fe1 radicals BH can be summarized as follows... 

Immediately upon addition of the urea-hydrogen peroxide adduct to the solution containing methyltrioxorhenium, a yellow color develops due to formation of the catalytically active rhenium peroxo complexes.3... 

The [Co(DH)2L] complexes react with oxygen 137) to give j -peroxo complexes LCo(DH)2-02-Co(DH)2L, isolated using several ligands (not isocyanides however). These adducts are labile, and oxygen is easily lost. On standing these complexes can undergo oxidation, however, to /x-superoxo... 

The reaction of (Bu NC)2Ni02 and hexafluoroacetone at —50° C yields a cyclic peroxo complex (XXXVIII) which loses one oxygen on dissolution in ether to give (XXXIX). 

In the same spirit DFT studies on peroxo-complexes in titanosilicalite-1 catalyst were performed [3]. This topic was selected since Ti-containing porous silicates exhibited excellent catalytic activities in the oxidation of various organic compounds in the presence of hydrogen peroxide under mild conditions. Catalytic reactions include epoxidation of alkenes, oxidation of alkanes, alcohols, amines, hydroxylation of aromatics, and ammoximation of ketones. The studies comprised detailed analysis of the activated adsorption of hydrogen peroxide with... 

Fe-Catalyzed Oxidation Reactions of Olefins, Alkanes, and Alcohols Involvement of Oxo- and Peroxo Complexes... 

Because there exist a number of reviews which deals with the structural and mechanistic aspects of high-valent iron-oxo and peroxo complexes [6,7], we focus in this report on the application and catalysis of iron complexes in selected important oxidation reactions. When appropriate we will discuss the involvement and characterization of Fe-oxo intermediates in these reactions. 

---