Osmium chloride bonding

Vinylidene osmium(O) (187) (Section II,B,3,g) reacts with sulfur, selenium, or copper chloride to give complexes 233 via electrophilic addition to the osmium-carbon bond (116) (Scheme 18). Complex 187 also reacts with benzoylazide to form the five-membered metallacycle 234 (Z) which isomerizes 234 (E) on heating in benzene (141). 

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]. 

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... 

Viridifloric /3-lactone, 143, has been identified as one of the pheromone components of a complex mixture of volatiles released by the pheromone glands of the male Idea leuconoe butterfly during courtship <1996BMC341>. A racemic mixture of both diastereoisomers was synthesized in four steps from the dilithio salt of 3-methylbutyric acid 144 alkylation with ethanal, dehydration of the secondary alcohol with phosphorus pentoxide, dihydroxylation of the C-C double bond with osmium tetraoxide, and finally formation of the /3-lactone by cyclization with sulfonyl chloride. By comparison with the sample isolated from I. leuconoe, the absolute configuration was established to be (2V,3V)-2-hydroxy-2-(l-methylethyl)-3-butanolide 143. 

The reactivity of the carbene transfer agent ImMes2.AgCl towards a variety of osmium clusters (Os3(p-H)2(CO)i0, Os3(CO)i0(NCMe)2, Os4(p-H)4(CO)i2) and Ru4(p-H)4(CO)i2 has been examined, and a number of new NHC complexes resulting from C-H and C-N bond activation reported (29 -34), including examples containing coordinated silver and chloride atoms.31... 

A THC and other active constituents are believed to be metabolically converted to substances oxidized at C(7), and this oxidation has been carried out by osmium tetroxide hydroxylation of A THC (333) and subsequent removal of the tertiary hydroxy-group (Scheme 20). The isomerization of the double bond to A THC is most conveniently carried out by photo-isomerization in propan-2-ol and xylene for 14 days, " although a second method is available that depends on an El elimination reaction of the hydrogen chloride adduct of A THC, using a sterically hindered base (after blocking the phenolic hydroxy-group). ... 

Polymers containing all metal backbones of Ru-Ru or Os-Os bonds have been prepared via the electrochemical reduction of ruthenium and osmium complexes containing /ram-chloride ligands.81,82 Scheme 2.6 shows the synthesis of polymers with their backbones comprised solely of metal-metal bonds. The polymers were prepared by reducing [Mn(/ran.s-Cl2)(bipyXCO)2] (M = Ru, Os), 33, to M° complexes and forming the polymer after the loss of the chloride ligands. In both cases, the polymers were selective for the reduction of carbon dioxide. 

The previously suggested structure (71) for isolongistrobine has been confirmed by synthesis (Scheme 4). TTie amino-alcohol (69) available from related synthetic work (see Vol. 4 of these Reports), was acylated with 4-pentenoyl chloride to give (70), which upon successive oxidation with Cornforth s reagent and oxidative double-bond cleavage with sodium periodate-osmium tetroxide gave isolongistrobine (71)-... 

The chemical behaviour of 133 is a result of two factors the high basicity of the metallic center, as a consequence of the presence of the strong donor phosphine and the chloride ligands in the complex, and the large steric hindrance experienced by the triisopropylphosphine groups, which are mutually cis disposed. This mixture allows access to reactive points on the osmium center by activation of Os-P and Os-Cl bonds. 

Electrophilic Addition.—The hydroxylation of alkenes, including several steroids, with osmium tetroxide has been reviewed. Addition of HOBr to the 19-functionalized-5a-cholest-6-enes (13) gave mixtures of the corresponding bromohydrins (14) and the 6,19-epoxides (15) whereas the analogous B-homo-compounds (16) gave only the 6,19-epoxides (17). Similar effects were noted for the related HBr- and HC104-catalysed opening of the 6a,7a-epoxides and it was observed that the predominant attack by the 19-0 atom [5(0)" attack] in the B-homo-series lay in the possibility of its linear approach with the C-6—Br or C-6—O bond. The reactions of chromyl chloride and chromyl fluoride with steroidal alkenes and dienes have been reported " and it was observed that the... 

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