Surface-mediated syntheses of Os5C CO

In solution, [Os5C(CO)i4] is obtained in low yields (ca 37%) from [Os3(CO)i2] by a multi-step process involving pyrolysis of the latter cluster to give [Os5C(CO)i5] followed by reaction with Na2C03 in methanol.  

Adsorption of [Os3(CO)i2] on to MgO, pretreated at 400 °C, followed by treatment for 4 h with a flow of CO (1 atm) at 275 °C, generates [Os5C(CO)i4] . Extraction with [(Ph3P)2N]Cl dissolved in acetone affords this anionic cluster in 65% 

Treatment of silica-supported [Os(CO)3Cl2]2 (2-5% w/w) of Os relative to Si02) with a slurry of K2CO3 (molar ratio K2CO3/OS = 20 1) in CH2CI2, followed by evaporation of the solvent and reaction with CO (1 atm) at 265 °C for 24 h affords K2[Os5C(CO)h] which can be extracted with CH3CN (74% yield)J This silica-mediated synthesis is much more efficient than the best known synthesis in solutionj  

4 The understanding of the process of nucleation of surface osmium(II) carhonyl species to osmium carhonyl clusters 

When the reductive carbonylation (1 atm CO or CO -h H2) of H2OSCI6 supported on MgO is performed at 200-250 °C the only surface carbonyl species detected are osmium(II) di- and tricarbonyl species of the type [Os(CO) c OMg 2] x = 2 or 3). These surface intermediates are quite stable under CO or CO -i- H2 and are reduced to give anionic osmium clusters only at temperatures approaching 275 °C. The reduction of the osmium(II) subcarbonyl species and the initiation of cluster growth were found to coincide with the loss of chemically bound water from the MgO surface, which becomes significant only at temperatures exceeding 250 °C. 

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