Osmium hydride

Chemical ingenuity in using the properties of the elements and their compounds has allowed analyses to be carried out by processes analogous to the generation of hydrides. Osmium tetroxide is very volatile and can be formed easily by oxidation of osmium compounds. Some metals form volatile acetylacetonates (acac), such as iron, zinc, cobalt, chromium, and manganese (Figure 15.4). Iodides can be oxidized easily to iodine (another volatile element in itself), and carbonates or bicarbonates can be examined as COj after reaction with acid. 

Other volatile compounds of elements can be used to transport samples into the plasma flame. For example, hydride reduction of mercury compounds gives the element (Hg), which is very volatile. Osmium can be oxidized to its volatile tetroxide (OSO4), and some elements can be measured as their volatile acetylacetonate (acac) derivatives, as with Zn(acac)2. 

Like mthenium, amines coordinated to osmium in higher oxidation states such as Os(IV) ate readily deprotonated, as in [Os(en) (NHCH2CH2NH2)] [111614-75-6], This complex is subject to oxidative dehydrogenation to form an imine complex (105). An unusual Os(IV) hydride, [OsH2(en)2] [57345-94-5] has been isolated and characterized. The complexes of aromatic heterocycHc amines such as pyridine, bipytidine, phenanthroline, and terpyridine ate similar to those of mthenium. Examples include [Os(bipy )3 [23648-06-8], [Os(bipy)2acac] [47691-08-7],... 

Cyclodecanediol has been prepared by the hydrogenation of sebacoin in the presence of Raney nickel or platinum, by the reduction of sebacoin with aluminum isopropoxide or lithium aluminum hydride, and by the oxidation of cyclodecene with osmium tetroxide and pyridine. ... 

Since electronegative groups at C-20 or C-21 deactivate a A hdouble bond towards attack by osmium tetroxide, Swiss workers have devised procedures wherein these groups are first reduced with lithium aluminum hydride, and the resulting aluminum complexes are then treated with osmium tetroxide... 

The crystalline material was shown to be modified sesquiterpinoid (5) containing two aldehyde functions, one of which is a,/3-unsat-urated (la). It analyzed for C13H22O2 and formed the dioxime. It readily took up oxygen on standing and was converted to the diol on treatment with lithium aluminum hydride. The bisdinitrobenzoate of this diol with osmium tetroxide yielded the tetraol, bisdinitrobenzoate, which was not readily acetylated. 

The sterically unbiased dienes, 5,5-diarylcyclopentadienes 90, wherein one of the aryl groups is substituted with NO, Cl and NCCHj), were designed and synthesized by Halterman et al. [163] Diels-Alder cycloaddition with dimethyl acetylenedicarbo-xylate at reflux (81 °C) was studied syn addition (with respect to the substituted benzene) was favored in the case of the nitro group (90a, X = NO ) (syrr.anti = 68 32), whereas anti addition (with respect to the substituted benzene) is favored in the case of dimethylamino group (90b, X = N(CH3)2) (syn anti = 38 62). The facial preference is consistent with those observed in the hydride reduction of the relevant 2,2-diaryl-cyclopentanones 8 with sodium borohydride, and in dihydroxylation of 3,3-diarylcy-clopentenes 43 with osmium trioxide. In the present system, the interaction of the diene n orbital with the o bonds at the (3 positions (at the 5 position) is symmetry-forbidden. Thus, the major product results from approach of the dienophile from the face opposite the better n electron donor at the (3 positions, in a similar manner to spiro conjugation. Unsymmetrization of the diene % orbitals is inherent in 90, and this is consistent with the observed facial selectivities (91 for 90a 92 for 90b). 

The preparation of Pans-1,2-cyclohexanediol by oxidation of cyclohexene with peroxyformic acid and subsequent hydrolysis of the diol monoformate has been described, and other methods for the preparation of both cis- and trans-l,2-cyclohexanediols were cited. Subsequently the trans diol has been prepared by oxidation of cyclohexene with various peroxy acids, with hydrogen peroxide and selenium dioxide, and with iodine and silver acetate by the Prevost reaction. Alternative methods for preparing the trans isomer are hydroboration of various enol derivatives of cyclohexanone and reduction of Pans-2-cyclohexen-l-ol epoxide with lithium aluminum hydride. cis-1,2-Cyclohexanediol has been prepared by cis hydroxylation of cyclohexene with various reagents or catalysts derived from osmium tetroxide, by solvolysis of Pans-2-halocyclohexanol esters in a manner similar to the Woodward-Prevost reaction, by reduction of cis-2-cyclohexen-l-ol epoxide with lithium aluminum hydride, and by oxymercuration of 2-cyclohexen-l-ol with mercury(II) trifluoro-acetate in the presence of ehloral and subsequent reduction. ... 

A ruthenium porphyrin hydride complex was lirst prepared by protonation of the dianion, [Ru(TTP) in THF using benzoic acid or water as the proton source. The diamagnetic complex, formulated as the anionic Ru(If) hydride Ru(TTP)(H )(THF)l , showed by H NMR spectroscopy that the two faces of the porphyrin were not equivalent, and the hydride resonance appeared dramatically shifted upheld to —57.04 ppm. The hydride ligand in the osmium analogue resonates at —66.06 ppm. Reaction of [Ru(TTP)(H)(THF)j with excess benzoic-acid led to loss of the hydride ligand and formation of Ru(TTP)(THF)2. 

Analogously, for preparation of racemic carba-a-glucopyranose 49 from 52, esterification of (—)-52 furnished the ester 95, which was transformed into compound 96 by debromination with zinc dust and acetic acid. Stereoselective hydroxylation of 96 with osmium tetraoxide and hydrogen peroxide, followed by acetylation, gave compound 97. Lithium aluminum hydride reduction of 97, and acetylation of the product, gave pentaacetate 98, which was converted into 99 by hydrolysis. ... 

Starting from 149, novel carba-sugar pentaacetates of the P-L-allo (168) and a-u-manno (171) configuration have been synthesized. Reduction of 149 with diisobutylaluminum hydride (DIBAL-H) and acetylation gave a mixture of acetates 162 and 163. Hydroxylation of the mixture with osmium tetraoxide and hydrogen peroxide provided compounds 164 and 165 in the ratio of 9 1. Hydrolysis of 164 gave compound 166, which was transformed into 168 by a reaction analogous to that employed in the preparation of 157 from 153. 

The formation of these compounds has been rationalized according to Scheme 6. The reaction of Os (E )-CH=C 11 Ph C1 (C())( P Pr3)2 with n-BuLi involves replacement of the chloride anion by a butyl group to afford the intermediate Os (/i> CH=CHPh ( -Bu)(CO)(P Pr3)2, which by subsequent hydrogen (3 elimination gives OsH ( >CI I=CHPh (CO)( P Pr3)2. The intramolecular reductive elimination of styrene from this compound followed by the C—H activation of the o-aryl proton leads to the hydride-aryl species via the styrene-osmium(O) intermediate Os r 2-CH2=CHPh (CO)(P Pr3)2. In spite of the fact that the hydride-aryl complex is the only species detected in solution, the formation of OsH ( )-CH=CHPh L(CO)(P Pr3)2 and 0s ( )-CH=CHPh (K2-02CH)(C0)(P,Pr3)2 suggests that in solution the hydride-aryl complex is in equilibrium with undetectable concentrations of OsH ( )-CH=CHPh (CO)(P,Pr3)2. This implies that the olehn-osmium(O) intermediate is easily accessible and can give rise to activation reactions at both the olefinic and the ortho phenyl C—H bonds of the... 

Treatment of OsT rf-T BT XCOXP Pr with ethanol under reflux does not lead to the formation of OsH2(CO)2(P Pr3)2 but instead gives the hydride-methyl osmium(II) compound OsHMe(CO)2(P Pr3)2 in good yield. 2-Methoxyethanol behaves in a manner similar to ethanol, and the reaction with the tetrahydridoborate complex yields OsH(CH2OMe)(CO)2(P Pr3)2 (Scheme 38).79... 

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