Osmium carbonyl clusters oxidative addition

In many cases the reaction of osmium carbonyls and acetylenes does not stop at the first stages as in [56], [57], or [57]. Instead, two or more acetylene molecules are incorporated, and in some cases acetylene trimerization to benzenes takes place (182, 371, 379). Incorporation of two acetylene molecules can lead to metallacyclo-pentadiene clusters like [55] (126,168,171,182,184, 223, 371), or to metallacyclo-hexadienone clusters hke [59] (126, 223). And the complex [90], another intermediate, is related to [55] by an intramolecular oxidative addition reaction (168,169). 

Oxidation of metal clusters may also be performed by reaction with Bronsted-acids through straightforward addition of protons to metal backbone. Thus, carbonyl clusters of ruthenium, osmium and iridium are stable in acids and may be pro toned without decomposition. The H-NMR spectra of these carbonyls in concentrated sulfuric or trifluoroacetic acid indicate the formation of cationic metal hydrides ... 

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