Osmium oxide compounds

Organic compounds, 322 Osmium, oxidation numbers, 414 Oswald, W., 65... 

Organic imide ligands have also been used to stabilize high oxidation states. The best example of this is the osmium(VIII) compound Os(NBul)4, which has a distorted tetrahedral OsN4 core (N—Os—N 104.6-111.9° Os—N 1.750 A) [194],... 

The oxidative cleavage of C=C bond is a common type of reaction encountered in organic synthesis and has played a historical role in the structural elucidation of organic compounds. There are two main conventional methods to oxidatively cleave a C=C bond (1) via ozonol-ysis and (2) via oxidation with high-valent transition-metal oxidizing reagents. A more recent method developed is via the osmium oxide catalyzed periodate oxidative cleavage of alkenes. All these methods can occur under aqueous conditions. 

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Ruthenium and osmium form compounds corresponding to various states of oxidation, such as the following RuClg, RRuO, OsoOg, OsCl KoOsO. ... 

The only known fluorine containing compounds of octa-valent osmium are osmium trioxide difluoride, OsOgF, and its salts. Osmium dioxide tetrafluoride, OsOjFg, and osmium oxide hexafluoride, OsOFg, are unknown. 

Physical Aspects.—Osmium oxide pentafluoride was of special interest since it was, at the time of its discovery, the only unambiguously heptavalent osmium compound. It remains the sole heptavalent osminm compound, available in molecular form, under normal... 

The formation of osmium oxide pentafluoride is noteworthy on two counts. First, it represents an unusual osmium valence and secondly, it is evidently preferred to osmium dioxide tetrafluoiide which is an alternative product of the osmium-oxygen-fluorine system. The latter would, of course, involve all the osmium valence electrons in bonding and molecular species OsO,F, again involves osmium in only six-co-ordination. There is no evidence, however, that this compound can be formed, either by the oxyfluorination of osmium, or by the fluorination of the dioxide. 

In contrast, aromatic compounds are in general not oxidized by the high-valent osmium oxide despite their lower oxidation potentials as compared to those of ole-finic substrates. Thus, the donor strength of the hydrocarbon is apparently not a critical factor for efficient oxidation or oxygen transfer. In fact, olefinic and aromatic donors (Ar) behave very similarly in the formation of organometallic EDA... 

The initial work on the reaction of osmium tetroxide with olefins was carried out by Hofmann early in the last century [3,4]. In the 1930s, Criegee [5] showed that the addition of a base, such as pyridine, accelerates the reaction rate. Later on, catalytic variations of the reaction were developed employing relatively inexpensive reagents for the reoxidation of the osmate species [6]. More recently, several advances were achieved to immobilize the catalyst and to improve the catalytic oxidation chain. In particular, recent work couples the oxidation of the osmium(VI) compound to a green terminal oxidant such as air or hydrogen peroxide [7-9]. 

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