Osmium derivatives

Pyrolysis at 200°C of Os3(CO)j2 in a scaled, evacuated tube afforded a mixture of at least seven different carbonyl clusters which could be separated by thin-layer chromatography. In addition to some unreacted Os3(CO)i2, the new compounds, Os.i(CO)i3, Os5(CO)i6, Os6(CO)i8, Os8(CO)23, and Os8(CO)2iC, were identified by mass spectroscopy (58) the last compound was originally formulated as Oss(CO)i5C4 (61). Further pyrolysis of Os6(CO)i8 at 255°C gives the pentanuclear carbide derivative, Os5(CO)I5C, in 40% yield (59). 

In the presence of trace quantities of water, pyrolysis of Os3(CO)i2 at 230°C results in a mixture of hydride carbonyl clusters. The new deriva- 

The IR spectra of all of these compounds do not show absorptions due to bridging carbonyl groups, and the NMR spectra indicate that the hydrogen atoms are always in bridging positions. Future structural determinations of such an impressive series of polynuclear derivatives will make a considerable contribution to the chemistry of high nuclcarity clusters. Until now only the structures of Os6(CO) is and Os7(CO)2i have been determined (104). 

Yellow-green [Co6(CO)i5]2 is conveniently synthesized in high yields (80-90%) by merely heating under vacuum an cthanolic solution of [Co(EtOH)x][Co(CO)4]2, obtained.by the reaction of Co2(CO)8 with ethanol (35). An alternative route to this could be the reduction of Co4(CO)i2 with alkali metals (37), 

Cobaltocene behaves as a toluene-soluble pseudoalkali metal, and in this nonpolar solvent ionic products precipitate out as soon as they are formed. Thus, the reduction of Co4(CO)i2 with cobaltocene in toluene gives an intermediate that analyzes as [CoCp2][Co4(CO)io n], and which is probably dimeric. Unfortunately, its lability has prevented further characterization (37). 

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In the iron, ruthenium, and osmium derivatives, there are eases of r] re-switeh on thermolysis followed by the elimination of small ligands. Organo-ruthenium speeies eontaining pyrazol-l-ylborate or -methane ligands with bulky substituents often have uneoordinated pyrazol-l-yl moieties and agostie R—B(C) - - - M interaetion. The latter sometimes influenees the properties of the jj -eoordinated speeies as well. 

Both the 1 1 and the 1 2 bonded alkenes should show structural isomers, with, for the ethylene adduct, nonequivalence of the two protons bonded to the carbon. For substituted olefins, it is often possible to detect the presence of both isomeric forms, especially with the osmium derivatives. However, all these molecules are fluxional and the flux-... 

Eliminations from Os(CO)4RR occur by dinuclear mechanisms only if either R or R is H. A hydride on one metal is necessary to interact with a vacant coordination site on the other in the dinuclear transition state. With Os(CO)4H2, the vacant site is created by dissociation of CO. With Os(CO)4-(H)CH the vacant site is created by a facile rate-determining isomerization which we suggest is to an acetyl hydride. The unique instability of hydridoalkyl carbonyls thus is explained. The synthesis and properties of Os(CO)4(H)C2H and various polynuclear ethyl osmium derivatives show that (3-hydrogens have no significant effect on these elimination mechanisms. Dinuclear hydridoalkyls are excellent starting points for the synthesis of more complex polynuclear alkyls. 

Addition of acid to the /i3-acetylide complexes (92 M = Ru or Os) results in the formation of 93 (M = Ru or Os) by an acid-induced migration of the hydroxy group from carbon to metal (137). Only the orange osmium derivative could be isolated, and this was structurally characterized as the /i3-di phenylpropadienylidene complex shown. 

A notable example is the comparison of the osmium derivatives (entries 18 to 27) in which the porphyrin rings all seem to be planar, and the osmium always sits in the N4 plane of the porphyrin ring, irrespective of the oxidation states between 2 and 6 which are encountered in the Os ions involved. 

The first stannatrane containing a tin-metal bond, the osmium derivative 450, was synthesized from TEAA and a triiodostannyl osmium complex (Scheme 20)878. 

ARENE RUTHENIUM AND OSMIUM DERIVATIVES AS CATALYST PRECURSORS... 

The heterobimetallic complexes [N(n-Bu)4] [Os(N)R2(/u.-0)2Cr02] catalyze the selective oxidation of alcohols with molecular oxygen. A mechanism in which alcohol coordinates to the osmium center and is oxidized by B-hydrogen elimination (see -Hydride Elimination) is consistent with the data. The hydroxide adduct of OSO4, [0s(0H)204], with ferric cyanide and other co-oxidants catalyzes the oxidative dehydrogenation of primary aromatic and aliphatic amines to nitriles, the oxidation of primary alcohols to carboxylic acids, and of secondary alcohols to ketones. Osmium derivatives such as OsCb catalyze the effective oxidation of saturated hydrocarbons in acetonitrile through a radical mechanism. ... 

Almost simultaneously, a platinum complex, in which the metal atom is bonded directly to the fullerene cage, was prepared.[Fa91 ] The site of attachment is the 6 6 double bond, as for the osmium derivative. The carbon bond lengths in the fullerene complexed with Pt are also similar to neat Ceo and to the Os derivative described above. Further details and other metal attachments are described in a review paper.[Fa92]... 

Osmium tetroxide was heated with phthalonitrile to form an osmium derivative which was crystallized from concentrated sulfuric acid as the diamagnetic sulfato-osmium(IV) phthalocyanine 25). A six-coordinate sulfato-bridged structure was proposed, but no infrared data were cited in support of this idea. The complex is extremely soluble in concentrated sulfuric acid. The diamagnetism is unexpected. Osmium(IY) has a d4 configuration, and a moment above 2.0 B.M. might have been predicted. The... 

As compared with other platinum metals, osmium and iridium have some specific features to which they owe their names. Osmium derives from the Greek osme for smell since osmium oxide is volatile and has a peculiar smell. Iridium got its name from the variety of colouring of its salts (from the Greek iris for rainbow ). A painter could have prepared an entire palette from iridium paints if they were not so expensive. These unusual properties promoted the discovery of these platinum metals. 

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