Synthesis of anionic osmium carbonyl clusters

Surface-mediated syntheses of anionic osmium carbonyl clusters from neutral complexes, clusters, or salts require a surface of adequate basicity as the reaction medium. This has been achieved by two different approaches. The first is the use of an intrinsically strongly basic surface such as magnesia. The basicity of this surface can be easily varied by adjusting the temperature of the treatment. Increasing the temperature leads to gradual decarbonation and dehydroxylation of the surface with creation of very basic centers, and therefore to increased surface basicity.l Similar thermal behavior is observed with the less basic alumina surface.t l 

The second approach entails increasing the basicity of the surface of silica, a more neutral support, by treatment with an alkali metal carbonate.I In this latter case, the basicity of the surface is influenced by  

The surface basicity is affected not only by the amount of alkali metal carbonate added but also by its nature - there is clear evidence that silica-supported K2CO3 behaves as a stronger base than silica-supported Na2C03 (see Section 2.10.3.1), probably because of low solvation of the alkali metal carbonate on the silica surface and, therefore, stronger ion-pair interaction of with the rela- 

In solution, the anionic cluster [H30s4(C0)i2] can be synthesized by deprotonation of [H40s4(CO)i2] with KOH in methanol (75% yield) or by heating a solu- 

Treatment of adsorbed H2OSCI6 on MgO, pretreated at 400 °C, for 12 h with a flow of CO + H2 (equimolar) at 275 °C and under 11 atm affords [H30s4(CO)i2] which can be extracted with [(Ph3P)2N]Cl dissolved in CH2Cl2. However, during the reaction, 42% of the initial Os content is lost, presumably as volatile neutral 

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