Supported Osmium Catalyst

Herrmann and coworkers reported on the preparation of immobilized OSO4 on poly(4-vinyl pyridine) and its use in the dihydroxylation of alkenes by means of hydrogen peroxide [36]. However, the problems of gradual polymer decomposition and osmium leaching were not solved. 

In contrast to other typical 0s04-catalyzed dihydroxylations, where H20- Bu0H is used as the solvent system, the best yields were obtained in H20/acetone/CH3CN. While the reaction was successfully carried out using NMO, moderate yields were obtained using trimethylamine N-oxide, and much lower yields were observed using hydrogen peroxide or potassium ferricyanide. The catalyst was recovered quantitatively by simple filtration and reused several times. The activity of the recovered catalyst did not decrease even after the fifth use. 

A study of the rate of conversion of the starting material showed that the reaction proceeds faster using OSO4 than using the microencapsulated catal)rst This is ascribed to the slower reoxidation of the microencapsulated osmium ester with NMO, compared with simple OSO4. 

In this instance the dihydroxylation does not require slow addition of the olefin, and the catalyst can be recovered quantitatively by simple filtration and reused without loss of activity. 

The dihydroxylation of monosubstituted and disubstituted aliphatic olefins and cyclic olefins was successfully performed using this heterogeneous catalyst and 

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Figure 3.29 Hydroxylation of styrene using a supported osmium catalyst.

In the upper half of the figure, the left-hand section compares the resonance for a silica-supported osmium catalyst containing 1 wt% osmium with that for pure metallic osmium. The magnitude of the resonance is higher for the osmium dispersed on the support, the extent of increase being indicated by the difference spectrum in the lower left-hand section of the figure. This effect is similar to the results we reported for iridium and platinum dispersed on an alumina support (39). 

Figure 2. EXAFS spectra of supported osmium catalysts [35].

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)...

Figure 4. Contributions of nearest neighbor copper and osmium backscattering atoms (circles in fields B and C, respectively) to the EXAFS (solid line) associated with the osmium Ltjj absorption edge of a silica supported osmium-copper catalyst, me circles in field A represent the combined contributions resulting from the data analysis. Reproduced with permission from Ref. 12. Copyright 1981, American Institute of Physics.

Oxidative cleavage of alkenes using sodium periodate proceeds effectively in a monophasic solution of acetic acid, water, and THF with very low osmium content or osmium-free. The orders of reactivity of alkenes are as follows monosubstituted trisubstituted >1,2 disub-stituted > 1,1-disubstituted > tetrasubstituted alkynes.100 Cleavage with polymer-supported OSO4 catalyst combined with NaI04 allows the reuse of the catalyst.101... 

Polymer-supported benzenesulfonyl azides have been developed as a safe diazotransfer reagent. ° These compounds, including CH2N2 and other diazoalkanes, react with metals or metal salts (copper, paUadium, and rhodium are most commonly used) to give the carbene complexes that add CRR to double bonds. Diazoketones and diazoesters with alkenes to give the cyclopropane derivative, usually with a transition-metal catalyst, such as a copper complex. The ruthenium catalyst reaction of diazoesters with an alkyne give a cyclopropene. An X-ray structure of an osmium catalyst intermediate has been determined. Electron-rich alkenes react faster than simple alkenes. ... 

Comparison of Activities of Supported Osmium Cluster Catalysts for Alkene Isomerization" (15)... 

Figure 4.13 Normalized EXAFS data at 100°K (osmium Lm absorption edge), with associated Fourier transforms, for pure metallic osmium and a silica-supported osmium-copper catalyst containing 2 wt% Os and 0.66 wt% Cu (32). (Reprinted with permission from the American Institute of Physics.)...

The size of the osmium-copper clusters of interest in the catalyst considered here is such that the number of metal atoms which could be present in a full surface layer is significantly higher than the number that would be located in the interior core. For a stoichiometry of one copper atom per osmium atom, there are, then, too few copper atoms to form a complete surface layer around the osmium. It should be realized that parameters derived from the EXAFS data on the osmium-copper clusters are average values, since there is very likely a distribution of cluster sizes (9) and compositions in a silica-supported osmium-copper catalyst. 

For the catalyst containing osmium alone on silica, the osmium clusters behave as if they are more electron deficient than pure metallic osmium that is, there appear to be more unfilled d states to accommodate the electron transitions from the 2pin core level of the absorbing atom. In the silica-supported osmium-copper clusters, however, the osmium atoms appear to be less electron deficient than they are in the pure osmium clusters dispersed on silica. The presence of the copper thus appears to decrease the number of unfilled d states associated with the osmium atoms. This observation is the first that we have made regarding the electronic interaction between the components of a bimetallic cluster catalyst. Further studies of such interactions are currently in progress on other bimetallic catalysts. 

Osmium catalysts prepared principally from osmium carbonyls, supported on alumina, have also been found to show antipathetic structure sensitivity (308). 

Zelinsky and Turowa-Pollak141 describe the specific properties of an osmium catalyst. Hydrogenation on osmium catalysts usually occurs at lower temperatures than on platinum, palladium, or nickel catalysts. Osmium asbestos is a very resistant catalyst that can be used for months on end without loss in activity disadvantages are that osmium catalysts that are not supported on carriers must be frequently regenerated and that when the temperature exceeds 150° osmium tends to decompose the material under hydrogenation. 

TABLE 9.9. Products of the Reactions of 2-Butyne with Deuterium over Alumina-Supported Ruthenium and Osmium Catalysts... 

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