Hydride osmium carbonyl derivatives

Some tetrametallic osmium carbonyl hydrides analogous to the rutheniixn carbonyl hydrides have been prepared. Trace quantities of the tetrametallic derivatives Hi 0sij(C0)i2 nd H20si,(CO)i3 are obtained along with the trimetallic derivatives (e.g., H20s3(C0)iq and H0s3(C0)iqOH, p. 355) from the reaction of Os3(CO)i2 with either methanolic potassium hydroxide or sodium borohydride, followed by phosphoric acid acidification (208). These were identified by analyses... 

The interaction of water with the metal carbonyls of osmium and ruthenium has proved to be a very facile route to the metal carbonyl hydrides (86). The corresponding oxygen derivative, H20s3(C0)90, has not been identified in these reactions. There is a wide range of products, summarized in the following chemical equations ... 

Eliminations from Os(CO)4RR occur by dinuclear mechanisms only if either R or R is H. A hydride on one metal is necessary to interact with a vacant coordination site on the other in the dinuclear transition state. With Os(CO)4H2, the vacant site is created by dissociation of CO. With Os(CO)4-(H)CH the vacant site is created by a facile rate-determining isomerization which we suggest is to an acetyl hydride. The unique instability of hydridoalkyl carbonyls thus is explained. The synthesis and properties of Os(CO)4(H)C2H and various polynuclear ethyl osmium derivatives show that (3-hydrogens have no significant effect on these elimination mechanisms. Dinuclear hydridoalkyls are excellent starting points for the synthesis of more complex polynuclear alkyls. 

Some tetrametallic carbonyl hydrides of iron, ruthenium, and osmium with mixed metal tetrahedra are also known. Thus reaction of either Ru3(CO)i2 [Ru(CO)3CI2]2 with excess Fe(C0)5 at its boiling point gives in addition to the trimetallic derivatives M2M (CO)12 (M and M = Fe or Ru in all possible combinations see p. 328) the orange iron-triruthenium tetrametallic derivatives H2PeRu3(CO)12 (381, 382). 

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