Osmium structures

Egbert JD, Bullock RM, Heinekey DM (2007) Cationic dihydrogen/dihydride complexes of osmium structure and dynamics. Organometallics 26 2291-2295... 

Another method for the hydroxylation of the etliylenic linkage consists in treatment of the alkene with osmium tetroxide in an inert solvent (ether or dioxan) at room temperature for several days an osmic ester is formed which either precipitates from the reaction mixture or may be isolated by evaporation of the solvent. Hydrolysis of the osmic ester in a reducing medium (in the presence of alkaline formaldehyde or of aqueous-alcoholic sodium sulphite) gives the 1 2-glycol and osmium. The glycol has the cis structure it is probably derived from the cyclic osmic ester ... 

A catalytic enantio- and diastereoselective dihydroxylation procedure without the assistance of a directing functional group (like the allylic alcohol group in the Sharpless epox-idation) has also been developed by K.B. Sharpless (E.N. Jacobsen, 1988 H.-L. Kwong, 1990 B.M. Kim, 1990 H. Waldmann, 1992). It uses osmium tetroxide as a catalytic oxidant (as little as 20 ppm to date) and two readily available cinchona alkaloid diastereomeis, namely the 4-chlorobenzoate esters or bulky aryl ethers of dihydroquinine and dihydroquinidine (cf. p. 290% as stereosteering reagents (structures of the Os complexes see R.M. Pearlstein, 1990). The transformation lacks the high asymmetric inductions of the Sharpless epoxidation, but it is broadly applicable and insensitive to air and water. Further improvements are to be expected. 

Figure 8.40 The k ySk) extended X-ray absorption fine structure (EXAFS) signal, Fourier transformed and then retransformed after application of the filter window indicated, in (a) osmium metal and (b) a 1% osmium catalyst supported on silica. (Reproduced, with permission, Ifom Winnick, FI. and Doniach, S. (Eds), Synchrotron Radiation Research, p. 413, Plenum, New York, 1980)...

Ruthenium and osmium have no oxides comparable to those of iron and, indeed, the lowest oxidation state in which they form oxides is -t-4. RUO2 is a blue to black solid, obtained by direct action of the elements at 1000°C, and has the rutile (p. 961) structure. The intense colour has been suggested as arising from the presence of small amounts of Ru in another oxidation state, possibly - -3. 0s02 is a yellowish-brown solid, usually prepared by heating the metal at 650°C in NO. It, too, has the rutile structure. 

Ruthenium and osmium form only disulfides. These have the pyrite structure and are diamagnetic semiconductors this implies that they contain M . RuSc2, RuTc2, OsSc2 and OsTc2 are very similar. All 6 dichalcogenides are obtained directly from the elements. 

The most important members of this class are the osmium nitrido, and the osmyl complexes. The reddish-purple K2[OsNCl5] mentioned above is the result of reducing the osmiamate. The anion has a distorted octahedral structure with a formal triple bond Os=N (161pm) and a pronounced /ram-influence (pp. 1163-4), i.e. the Os-Cl distance trans to Os-N is much longer than the Os-Cl distances cis to Os-N (261 and 236 pm respectively). The anion [OsNCls] also shows a rram-effect in that the Cl opposite the N is more labile than the others, leading, for instance, to the formation of [Os NCl4] , which has a square-pyramidal structure with the N occupying the apical position. 

Osmium tetroxide, reaction with alkenes, 235-236 toxicity of, 235 Oxalic add, structure of, 753 Oxaloacetic acid, structure of, 753 Oxetane, reaction with Grignard reagents, 680 Oxidation, 233, 348 alcohols, 623-626 aldehydes, 700-701 aldoses, 992-994 alkenes, 233-236 biological, 625-626 phenols, 631 sulfides, 670 thiols, 668... 

It has 6-coordinate osmium in a structure (Figure 1.2) regarded as being made from a hexagonally packed array of chlorides with osmiums occupying half the holes in alternate layers Os-Cl bond lengths are 2.261 A (terminal) and 2.378 A (bridge) [20]. 

Black OsBr4 (PtX4 structure) has 6-coordinate osmium [21]... 

Oxychlorides are less prolific, apart from the red-brown OsOCl4 (m.p. 32°C). This probably has a molecular structure in the solid state as the IR spectra of the solid, matrix-isolated and gas-phase molecules are very similar, and the volatility is consonant with this [30]. Syntheses include heating osmium in a stream of oxygen/chlorine ( oxychlorination ) and by ... 

The complexes of ruthenium and osmium in the same oxidation state are generally similar and are, therefore, treated together the structural (Table 1.3) and vibrational data (Table 1.4) have been set out in some detail to demonstrate halogen-dependent trends. 

Considerable structural information is available on osmium complexes of tertiary phosphines, arsines and stibines (Table 1.13) [152, 157]. 

Both of these elements are silver-white lustrous metals with high melting (ruthenium 2310°C, osmium 3900°C) and boiling (3900 and 5510°C, respectively) points. As usual, the 5d metal is much more dense (ruthenium 12.45, osmium 22.59gem-3) both adopt hep structures osmium is the densest metal known. The metals are unreactive, insoluble in all acids, even aqua regia. Ruthenium tends to form a protective coating of the dioxide and is not attacked by oxygen below 600°C nor by chlorine or fluorine below... 

Osmium, quinuclidinetetraoxime-stereochemistry, 1,44 Osmium, tetrachloronitrido-tetraphenylarsenate stereochemistry, 1,44 Osmium, tris(l,l0-phenanthro1ine)-structure, 1, 64... 

Bullitt, J. G. Cotton, F. A. (1971) The structure of a dinuclear complex of osmium(I) with a metal-to-metal single bond bis-(/i-acetatojhexacarbonyldiosmium, Inorg. Chim. Acta. 5, 406-412. 

ABA type poly(hydroxyethyl methacrylate) (HEMA) and PDMS copolymers were synthesized by the coupling reactions of preformed a,co-isocyanate terminated PDMS oligomers and amine-terminated HEMA macromonomers312). Polymerization reactions were conducted in DMF solution at 0 °C. Products were purified by precipitation in diethyl ether to remove unreacted PDMS oligomers. After dissolving in DMF/toluene mixture, copolymers were reprecipitated in methanol/water mixture to remove unreacted HEMA oligomers. Microphase separated structures were observed under transmission electron microscope, using osmium tetroxide stained thin copolymer films. 

Dendrimers can be constructed from chemical species other than purely organic monomers. For example, they can be built up from metal branching centres such as ruthenium or osmium with multidentate ligands. The resulting molecules are known as metallodendrimers. Such molecules can retain their structure by a variety of mechanisms, including complexation, hydrogen bonding and ionic interactions. 

The first ruthenium porphyrin alkyls to be reported were prepared from the zerovalent dianion, [Ru(Por)] with iodomethane or iodocthane, giving the ruthe-nium(lV) dialkyl complexes Ru(Por)Me2 or Ru(Por)Et2 (Por = OEP, TTP). Alternatively, the Ru(lV) precursors Ru(Por)X2 react with MeLi or ArLi to produce Ru(Por)Mc2 or Ru(Por)Ar2 (Ar = / -C(,H4X where X = H, Me, OMe, F or Cl) 147-149 The osmium analogues can be prepared by both methods, and Os(Por)R2 where R = Me, Ph and CH2SiMe2 have been reported.Some representative structures are shown in Fig. 5, and the preparation and interconversion of ruthenium porphyrin alkyl and aryl complexes are shown in Scheme 10. 

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