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Triosmium dodecacarbonyl

Triosmium dodecacarbonyl

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Triosmium dodecacarbonyl is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula Os3(CO)12. This yellow-colored metal carbonyl cluster
Cluster chemistry
In chemistry, a cluster is an ensemble of bound atoms intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group...

 is an important precursor to organo-osmium compounds
Organometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...

. Many of the advances in cluster chemistry have arisen from studies on derivatives of Os3(CO)12 and its lighter analogue Ru3(CO)12
Triruthenium dodecacarbonyl
Triruthenium dodecacarbonyl is the chemical compound with the formula Ru312. This orange-colored metal carbonyl cluster is a precursor to other organoruthenium compounds.-Structure and synthesis:...

.

Structure and synthesis


The cluster has D3h symmetry
Molecular symmetry
Molecular symmetry in chemistry describes the symmetry present in molecules and the classification of molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can predict or explain many of a molecule's chemical properties, such as its dipole moment...

, consisting of an equilateral triangle of Os atoms, each of which bears two axial and two equatorial CO
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

s. The Os–Os bond distance is 2.88 Â (288 pm). Ru3(CO)12 has the same structure, whereas Fe3(CO)12 is different, with two bridging CO ligands resulting in C2v symmetry.

Os3(CO)12 is prepared by the direct reaction of OsO4 with carbon monoxide at 175 °C:
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
Acetonitrile
Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...

) and Os3(CO)10(MeCN)2 using Me3NO
Trimethylamine N-oxide
Trimethylamine N-oxide, also known by several other names and acronyms, is the organic compound with the formula 3NO. This colorless solid is usually encountered as the dihydrate. It is an oxidation product of trimethylamine and a common metabolite in animals. It is an osmolyte found in saltwater...

 as a decarbonylating agent. Os3(CO)11(MeCN) reacts with a variety of even weakly basic ligands to form adducts such as Os3(CO)11(ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

) and Os3(CO)11(pyridine
Pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...

). The direct reaction of Os3(CO)12 with ethylene and pyridine results in degradation of these organic ligands to give the vinyl
Vinyl
A vinyl compound is any organic compound that contains a vinyl group ,which are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group...

 hydride HOs3(CO)10(η
Hapticity
The term hapticity is used to describe how a group of contiguous atoms of a ligand are coordinated to a central atom. Hapticity of a ligand is indicated by the Greek character 'eta', η. A superscripted number following the η denotes the number of contiguous atoms of the ligand that are bound to...

12-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, the molecule CH3(H)Os3(CO)10 provided one of the first clear-cut examples of agostic bonding
Agostic interaction
Agostic interaction is a term in organometallic chemistry for the interaction of a coordinately-unsaturated transition metal with a C-H bond, when the two electrons involved in the C-H bond enter the empty d-orbital of a transition metal, resulting in a three-center two-electron bond. Many...

.

From the perspective of bonding
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

, the molecule H2Os3(CO)10
Decacarbonyldihydridotriosmium
Decacarbonyldihydridotriosmium is a chemical compound with the formula H2Os310. This purple-violet crystalline air-stable cluster is noteworthy because it is electronically unsaturated and hence adds a variety of substrates.-Structure and synthesis:...

 is noteworthy. In this compound, the two hydride ligands bridge one Os-Os edge. The molecule displays reactivity reminiscent of diborane
Diborane
Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...

.