Osmium oxo complexes

Mono(p-oxo) complexes, osmium, 37 311 Monooxygenases, Fe—S clusters as electron carriers, 38 305... 

This behavior, as well as complementary observations, can be explained on the basis of the reaction mechanism depicted in Scheme 5.3. The main catalytic cycle involves three successive forms of the enzyme in which the iron porphyrin prosthetic group undergoes changes in the iron oxidation state and the coordination sphere. E is a simple iron(III) complex. Upon reaction with hydrogen peroxide, it is converted into a cation radical oxo complex in which iron has a formal oxidation number of 5. This is then reduced by the reduced form of the cosubstrate, here an osmium(II) complex, to give an oxo complex in which iron has a formal oxidation number of 4. 

Among oxo-metals, osmium tetroxide is a particularly intriguing oxidant since it is known to oxidize various types of alkenes rapidly, but it nonetheless eschews the electron-rich aromatic hydrocarbons like benzene and naphthalene (Criegee et al., 1942 Schroder, 1980). Such selectivities do not obviously derive from differences in the donor properties of the hydrocarbons since the oxidation (ionization) potentials of arenes are actually less than those of alkenes. The similarity in the electronic interactions of arenes and alkenes towards osmium tetroxide relates to the series of electron donor-acceptor (EDA) complexes formed with both types of hydrocarbons (26). Common to both arenes and alkenes is the immediate appearance of similar colours that are diagnostic of charge-transfer absorp-... 

Ruthenium and Osmium High Oxidation States S.6.2.3 Oxo Complexes... 

There are a number of osmium(VI) oxo complexes containing cyanide ligand, but none have been reported for ruthenium. The ion [0s(0)2(CN)4] can be prepared by reaction of [OSO4] with aqueous KCN. The X-ray crystal structure of Cs2[Os(0)2(CN)4] (85) shows that it has trans-6ioxo groups with 0s=0 distances of 1.750 [0s(0)2(CN)4] is luminescent both in the solid state... 

Table 6 Summary of formal potentials for selected ruthenium and osmium oxo complexes.

There are few well-characterized high-valent peroxo complexes of ruthenium and osmium, presumably because they decompose readily to give oxo complexes. 

Quercetinase, 44 281 Quinlol complexes, osmium, 37 270 1,5-Quinoid-7,8-dihydro-6//-L-biopterin, pro-tonated, oxo-Mo(IV) complex, 40 11-12 Quinone complexes... 

Selected Metal-Oxo Bond Distances and Stretching Frequencies for Ruthenium and Osmium Oxo Complexes... 

A new class of binuclear nitrido complexes of tetravalent osmium and ruthenium is described in which the metal atoms are symmetrically bridged by a nitride ligand to give a linear M-N—M unit They have the stoichiometries M2NX8(H20)2]3 and [M2N(NH3)8Y2]3+ (M = Os, Ru X = Cl, Br Y = Cl, Br, etc.). Studies are reported on their vibrational spectra, structures, and bonding. Preliminary studies are reported also on trinuclear complexes of osmium and iridium. Finally, the use of vibrational spectroscopy in the study of metal-nitrido and metal-oxo complexes is discussed briefly. 

The oxo complexes of osmium dominate the chemistry of the element, the duster carbonyls notwithstanding, and the tetroxide is the single most important compound of the element. 

The arrangement of this large section on osmium oxo complexes follows the pattern of other sections in this chapter. We consider mononuclear complexes first, by increasing oxidation state and, within each oxidation state, we consider those complexes with the largest number of oxo ligands first. The same procedure is then followed for binuclear species. For convenience, however, mononuclear and polynuclear oxo esters are considered together. 

Obviously the chemistry here is dominated by that of the tetroxide. We briefly consider the hexa-and penta-oxo species, then Os04, followed by species of the type Os04 L and OsO, . The few tri-, di- and mono-oxo complexes of osmium(VIII) conclude the section, (see Table 23). 

As with nitrido and oxo complexes we shall consider osmium nitrosyl (NO) complexes as a group, irrespective of the nature of the other ligands present. Just as N " and are strong n donors and... 

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