Triosmium dodecacarbonyl

Triosmium dodecarbonyl is a chemical compound with the formula Os₃(CO)₁₂. This yellow colored metal carbonyl cluster is an important precursor to organo-osmium compounds. Many of the advances in cluster chemistry have arisen from studies on derivatives of Os₃(CO)₁₂ and its lighter analogue Ru₃(CO)₁₂.

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Structure and synthesis

The cluster has D_3h symmetry, consisting of an equilateral triangle of Os atoms, each of which bears two axial and two equatorial CO ligands. The Os–Os bond distance is 2.88 Â (288 pm).^[1] Ru₃(CO)₁₂ has the same structure, whereas Fe₃(CO)₁₂ is different, with two bridging CO ligands resulting in C_2v symmetry.

Os₃(CO)₁₂ is prepared by the direct reaction of OsO₄ with carbon monoxide at 175 °C:^[2]

3 OsO₄ + 24 CO → Os₃(CO)₁₂ + 12 CO₂

The yield is nearly quantitative.

Reactions

The chemical properties of Os₃(CO)₁₂ have been thoroughly examined. Direct reactions of ligands with the cluster often lead to complex product distributions because the inert Os–CO bonds require high temperatures to break, and at such high temperatures successive the initially formed adducts react further. More successfully, Os₃(CO)₁₂ is converted to more labile derivatives such as Os₃(CO)₁₁(MeCN) and Os₃(CO)₁₀(MeCN)₂ using Me₃NO as a decarbonylation agent.^[3] Os₃(CO)₁₁(MeCN) reacts with a variety of even weakly basic ligands to form adducts such as Os₃(CO)₁₁(ethylene) and Os₃(CO)₁₁(pyridine). The direct reaction of Os₃(CO)₁₂ with ethylene and pyridine results in degradation of these organic ligands to give the vinyl hydride HOs₃(CO)₁₀(η¹,η²-C₂H₃) and the pyridyl-hydride HOs₃(CO)₁₀(NC₅H₄). These products illustrate the stability of Os–H and Os–C bonds.

Os₃(CO)₁₂ is a platform to examine the ways that hydrocarbons can interact with ensembles of metals. For example, in Fischer-Tropsch processing, it is understood that the polymetallic catalysts assist the hydrogenation of CO to give hydrocarbons. Models for such intermediates are provided by the series CH₃(H)Os₃(CO)₁₀, (CH₂)(H)₂Os₃(CO)₁₀, and (CH)(H)₃Os₃(CO)₉.^[4] The molecule CH₃(H)Os₃(CO)₁₀ provided one of the first clear-cut examples of agostic bonding.^[5]

From the perspective of bonding, the molecule H₂Os₃(CO)₁₀ is noteworthy. In this compound, the two hydride ligands bridge one Os-Os edge. The molecule displays reactivity reminiscent of diborane.^[6]

References

1. ^ Corey, E. R.; Dahl, L. F. “The Molecular and Crystal Structure of Os₃(CO)₁₂” Inorganic Chemistry 1962, volume 1, pages 521 - 526. DOI: 10.1021/ic50003a016
2. ^ Drake, S. R.; Loveday, P. A. “Dodecarbonyltriosmium” Inorganic Syntheses, 1990, volume 28, pages 230-1. ISBN 0-471-52619-3.
3. ^ Nicholls, J. N.; Vargas, M. D. “Some Useful Derivatives of Dodecarbonyltriosmium” Inorganic Syntheses, 1990, volume 28, pages 232-5. ISBN 0-471-52619-3.
4. ^ Calvert, R. B.; Shapley, J. R. “Activation of Hydrocarbons by Unsaturated Metal Cluster Complexes. 6. Synthesis and Characterization of Methyldecacarbonylhydridotriosmium, Methylenedecacarbonyldihydridotriosmium, and Methylidynenonacarbonyltrihydridotriosmium. Interconversion of Cluster-Bound Methyl and Methylene Ligands” Journal of the American Chemical Society 1977, volume 99, 5225-6. DOI: 10.1021/ja00457a077
5. ^ Calvert, R. B.; Shapley, J. R. “Decacarbonyl(methyl)hydrotriosmium: NMR evidence for a Carbon^..Hydrogen^..Osmium Interaction” Journal of the American Chemical Society 1978, volume 100, pages 7726-7. DOI: 10.1021/ja00492a047
6. ^ Keister, J. B.; Shapley, J. R. “Solution Structures and Dynamics of complexes of Decacarbonyldihydrotriosmium with Lewis Bases” Inorganic Chemistry 1982, volume 21, pages 3304-10.DOI: 10.1021/ic00139a011DOI: 10.1021/ic00139a011