Organoruthenium chemistry
Encyclopedia
Organoruthenium chemistry is the chemistry
of organometallic compounds containing a carbon
to ruthenium
chemical bond
. The interest is mostly academic although several organoruthenium catalysts are of commercial interest. The chemistry has many similarities with organoiron chemistry
, as iron is directly above ruthenium in group 8
of the periodic table. The most important reagents for the introduction of ruthenium are ruthenium(III) chloride
and triruthenium dodecacarbonyl
. The related compound Ru(CO)5 is less attractive for this purpose because it decomposes:
In its organometallic compounds, ruthenium is known to adopt oxidation states from -2 ([Ru(CO)4]2-) to +6 ([RuN(Me)4]-). Most common are those in the 2+ oxidation state, as illustrated below.
s for ruthenium are:
is unreactive because it is coordinatively saturated and contains no reactive groups. Shvo's catalyst
({[Ph4(η5-C4CO)]2H]}Ru2(CO)4(μ-H)) is also coordinatively saturated, but features reactive OH and RuH groups that enable it to function in transfer hydrogenation
.. It is used in hydrogenation
of aldehydes, ketones, via transfer hydrogenation
, in disproportionation
of aldehydes to esters and in the isomerization of allylic alcohols.
Chloro(cyclopentadienyl)bis(triphenylphosphine)ruthenium
features a reactive chloro group, which is readily substituted by organic substrates.
, which is the precursor to a versatile catalyst for transfer hydrogenation
. Acenaphthylene
forms a useful catalyst derived from triruthenium dodecacarbonyl
. The hapticity
of the hexamethylbenzene
ligand in Ru(C6Me6)2 depends on the oxidation state of the metal centre (methyl groups omitted for clarity):
The compound Ru(COD
)(COT
) is capable of dimerizing norbornadiene
:
resembles ruthenium in its complexes. Because Os is more expensive than Ru, the chemistry is less developed and has fewer applications. Of course the cost of the catalyst is offset of turnover numbers are high. Thus, Osmium tetroxide is an important oxidizing agent in organic chemistry especially in the conversion of alkenes to 1,2-diols.
The 5d-orbitals in Os are higher in energy that the 4d-orbitals in Ru. Thus, π backbonding to alkenes and CO is stronger for Os compounds, which leads to more stable organic derivatives. This effect is illustrated by the stability of the alkene derivatives of the type or as in the example below.
Important compounds, at least for academic studies, are the carbonyls such as triosmium dodecacarbonyl
and decacarbonyldihydridotriosmium
. The phosphine complexes are analogous to those or ruthenium, but hydride derivatives tend to be more stable, e.g. OsHCl(CO)(PPh3)3.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
of organometallic compounds containing a carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
to ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
chemical bond
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 interest is mostly academic although several organoruthenium catalysts are of commercial interest. The chemistry has many similarities with organoiron chemistry
Organoiron chemistry
Organoiron chemistry is the chemistry of organometallic compounds containing a carbon-to-iron chemical bond. Organoiron compounds are relevant in organic synthesis as reagents such as iron pentacarbonyl, diiron nonacarbonyl and disodium tetracarbonylferrate. Iron adopts oxidation states from Fe...
, as iron is directly above ruthenium in group 8
Group 8 element
A Group 8 element is one in the series of elements in group 8 in the periodic table, which consists of the transition metals iron , ruthenium , osmium and hassium ....
of the periodic table. The most important reagents for the introduction of ruthenium are ruthenium(III) chloride
Ruthenium(III) chloride
Ruthenium chloride is the chemical compound with the formula RuCl3. "Ruthenium chloride" more commonly refers to the hydrate RuCl3·xH2O. Both the anhydrous and hydrated species are dark brown or black solids...
and triruthenium dodecacarbonyl
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:...
. The related compound Ru(CO)5 is less attractive for this purpose because it decomposes:
- Ru3(CO)12 + 3 CO
3 Ru(CO)5
In its organometallic compounds, ruthenium is known to adopt oxidation states from -2 ([Ru(CO)4]2-) to +6 ([RuN(Me)4]-). Most common are those in the 2+ oxidation state, as illustrated below.
Ligands
The most important ligandLigand
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 for ruthenium are:
- carbon monoxide as in metal carbonylMetal carbonylMetal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. These complexes may be homoleptic, that is containing only CO ligands, such as nickel carbonyl , but more commonly metal carbonyls contain a mix of ligands, such as Re3Cl...
s - phosphines. BINAPBINAPBINAP is an abbreviation for the organophosphorus compound 2,2'-bis-1,1'-binaphthyl. This chiral ligand is widely used in asymmetric synthesis. It consists of a pair of 2-diphenylphosphinonaphthyl groups linked at the 1 and 1´ positions. This C2-symmetric framework lacks stereogenic atom, but...
is an asymmetric ligand for many ruthenium compounds in asymmetric synthesis . - cyclopentadienylCyclopentadienylIn organic chemistry, cyclopentadienyl is a cyclic group of atoms with the formula C5H5. Cyclopentadienyl are closely related to cyclopentadiene. Cyclopentadienyl have five carbon atoms bonded together in a pentagonal planar ring, all five of which are bonded to individual hydrogen atoms...
ligands. - various arenes and dieneDieneIn organic chemistry a diene or diolefin is a hydrocarbon that contains two carbon double bonds.Conjugated dienes are functional groups, with a general formula of CnH2n-2. Dienes and alkynes are functional isomers...
s - metal carbenes, notably Grubbs' catalystGrubbs' catalystGrubbs' Catalyst is a transition metal carbene complex named after Robert H. Grubbs, the chemist who first synthesized it. There are two generations of the catalyst, as shown on the right. In contrast to other olefin metathesis catalysts, Grubbs' Catalysts tolerate other functional groups in the...
, an import catalyst in olefin metathesis. - halides. chlorineChlorineChlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
ligands are easily replaced by alkyl, aryl or hydride ligands - hydrogen. Transition metal hydrideTransition metal hydrideTransition metal hydrides are chemical compounds containing a transition metal bonded to hydrogen. Most transition metals form hydride complexes and some are significant in various catalytic and synthetic reactions...
s are important in C-H bond activationC-H bond activationCarbon–hydrogen bond activation or C−H activation may be defined as a reaction that cleaves a carbon–hydrogen bond. Often the term is restricted to reactions involving organometallic complexes and proceeding by coordination of a hydrocarbon to the inner-sphere of metal, either via an...
.
Cyclopentadienyl ligands
The parent compound ruthenoceneRuthenocene
Ruthenocene is an organoruthenium compound with the formula 2Ru. This pale yellow, volatile solid is classified as a sandwich compound and more specifically, as a metallocene.-Structure and bonding:...
is unreactive because it is coordinatively saturated and contains no reactive groups. Shvo's catalyst
Shvo catalyst
The Shvo catalyst, named after Youval Shvo, is an organoruthenium compound that is used for transfer hydrogenation. Related derivatives are known where p-tolyl replaces some of the phenyl groups.-Synthesis, structure, reactivity:...
({[Ph4(η5-C4CO)]2H]}Ru2(CO)4(μ-H)) is also coordinatively saturated, but features reactive OH and RuH groups that enable it to function in transfer hydrogenation
Transfer hydrogenation
Transfer hydrogenation is the addition of hydrogen to a molecule from a source other than gaseous H2. It is applied in industry and in organic synthesis, in part because of the inconvenience and expense of using gaseous H2...
.. It is used in hydrogenation
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
of aldehydes, ketones, via transfer hydrogenation
Transfer hydrogenation
Transfer hydrogenation is the addition of hydrogen to a molecule from a source other than gaseous H2. It is applied in industry and in organic synthesis, in part because of the inconvenience and expense of using gaseous H2...
, in disproportionation
Disproportionation
Disproportionation, also known as dismutation is used to describe a specific type of redox reaction in which a species is simultaneously reduced and oxidized so as to form two different products....
of aldehydes to esters and in the isomerization of allylic alcohols.
Chloro(cyclopentadienyl)bis(triphenylphosphine)ruthenium
Chloro(cyclopentadienyl)bis(triphenylphosphine)ruthenium
Chlorobisruthenium is the organoruthenium half-sandwich compound with formula RuCl2. It as an air-stable orange crystalline solid that is used in a variety of organometallic synthetic and catalytic transformations.-Structure and Properties:The compound has idealized Cs symmetry...
features a reactive chloro group, which is readily substituted by organic substrates.
Arene and alkene ligands
One example of an Ru-arene complex is (cymene)ruthenium dichloride dimer(Cymene)ruthenium dichloride dimer
ruthenium dichloride dimer is the organometallic compound with the formula [RuCl2]2. This red-coloured, diamagnetic solid is a reagent in organometallic chemistry and homogeneous catalysis.-Preparation and reactions:...
, which is the precursor to a versatile catalyst for transfer hydrogenation
Transfer hydrogenation
Transfer hydrogenation is the addition of hydrogen to a molecule from a source other than gaseous H2. It is applied in industry and in organic synthesis, in part because of the inconvenience and expense of using gaseous H2...
. Acenaphthylene
Acenaphthylene
Acenaphthylene is a polycyclic aromatic hydrocarbon consisting of naphthalene with an ethylene bridge connecting positions 1 and 8. It is a constituent of coal tar. Reduction of the ethylene group gives the related compound acenaphthene. Unlike most polycyclic aromatic hydrocarbons, it has no...
forms a useful catalyst derived from triruthenium dodecacarbonyl
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:...
. The hapticity
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...
of the hexamethylbenzene
Hexamethylbenzene
Hexamethylbenzene is white crystalline solid with chemical formula C66. It is a synthetic aromatic hydrocarbon with six methyl groups stemming from the carbon centres of the ring. Hexamethylbenzene has historical significance in the field of X-ray crystallography...
ligand in Ru(C6Me6)2 depends on the oxidation state of the metal centre (methyl groups omitted for clarity):
The compound Ru(COD
Cyclooctadiene
A cyclooctadiene is a cyclic diene with the formula C8H12. Focusing only on cis derivatives, four isomers are possible: 1,2, which is an allene, 1,3-, 1,4-, and 1,5-. Commonly encountered isomers are 1,3-cyclooctadiene and 1,5-cyclooctadiene, which is used as a ligand for transition...
)(COT
Cyclooctatetraene
1,3,5,7-Cyclooctatetraene is an unsaturated derivative of cyclooctane, with the formula C8H8. It is also known as [8]annulene. This polyunsaturated hydrocarbon is a colorless to light yellow flammable liquid at room temperature...
) is capable of dimerizing norbornadiene
Norbornadiene
Norbornadiene is an organic compound. This bicyclic hydrocarbon is the most stable diolefin derived from the norbornane and norbornene. Norbornadiene is primarily of interest as a ligand in homogeneous catalysis, but it has been heavily studied due to its high reactivity and distinctive...
:
Organoosmium
In the same group 8 elements osmiumOsmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
resembles ruthenium in its complexes. Because Os is more expensive than Ru, the chemistry is less developed and has fewer applications. Of course the cost of the catalyst is offset of turnover numbers are high. Thus, Osmium tetroxide is an important oxidizing agent in organic chemistry especially in the conversion of alkenes to 1,2-diols.
The 5d-orbitals in Os are higher in energy that the 4d-orbitals in Ru. Thus, π backbonding to alkenes and CO is stronger for Os compounds, which leads to more stable organic derivatives. This effect is illustrated by the stability of the alkene derivatives of the type or as in the example below.
Important compounds, at least for academic studies, are the carbonyls such as triosmium dodecacarbonyl
Triosmium dodecacarbonyl
Triosmium dodecacarbonyl is a chemical compound with the formula Os312. This yellow-colored metal carbonyl cluster is an important precursor to organo-osmium compounds...
and decacarbonyldihydridotriosmium
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:...
. The phosphine complexes are analogous to those or ruthenium, but hydride derivatives tend to be more stable, e.g. OsHCl(CO)(PPh3)3.
See also
- Chemical bonds of carbon with other elements in the periodic table: