Organorhodium chemistry

Last updated
Cyclooctadiene rhodium chloride dimer Cyclooctadiene-rhodium-chloride-dimer-2D-skeletal.png
Cyclooctadiene rhodium chloride dimer

Organorhodium chemistry is the chemistry of organometallic compounds containing a rhodium-carbon chemical bond, and the study of rhodium and rhodium compounds as catalysts in organic reactions. [1]

Contents

Stable organorhodium compounds and transient organorhodium intermediates are used as catalyst such as in olefin hydroformylation, olefin hydrogenation, olefin isomerization and the Monsanto process. [2]

Classification based on principal oxidation states

Organometallic rhodium compounds share many characteristics with those of iridium, but less so with cobalt. Rhodium can exist in oxidation states of -III to +V, but rhodium(I) and rhodium(III) are the more common. Rhodium(I) compounds (d8 configuration) usually occur with square planar or trigonal bipyramidal geometries, while rhodium (III) compounds (d6 configuration) typically have an octahedral geometry. [2]

Rhodium(0)

Rhodium(0) complexes are binary carbonyls, the principal examples being tetrarhodium dodecacarbonyl, Rh4(CO)12, and hexadecacarbonylhexarhodium, Rh6(CO)16. These compounds are obtained by reductive carbonylation of rhodium(III) salts or Rh2Cl2(CO)4. In contrast to the stability of the homologous Co2(CO)8, Rh2(CO)8 is very labile.

Rhodium(I)

Rhodium(I) complexes are important homogeneous catalysts. Common complexes include bis(triphenylphosphine)rhodium carbonyl chloride, chlorobis(ethylene)rhodium dimer, cyclooctadiene rhodium chloride dimer, chlorobis(cyclooctene)rhodium dimer, dicarbonyl(acetylacetonato)rhodium(I), and rhodium carbonyl chloride. Although not formally organometallic, Wilkinson's catalyst (RhCl(PPh3)3), is included in the list of important catalysts. The simple olefin complexes chlorobis(ethylene)rhodium dimer, chlorobis(cyclooctene)rhodium dimer, and cyclooctadiene rhodium chloride dimer are often used as sources of "RhCl", exploiting the lability of the alkene ligands or their susceptibility to removal by hydrogenation. (η5-Cp)RhL2 are derived from Rh2Cl2L4 (L = CO, C2H4).

Rhodium(II)

Unlike the prevalence of cobalt(II) complexes, compounds of rhodium(II) are rare. The sandwich compound rhodocene is one example, even it exists in equilibrium with a dimeric Rh(I) derivative. Although not organometallic, rhodium(II) acetate (Rh2(OAc)4) catalyzes cyclopropanations via organometallic intermediates. Rhodium(II) porphyrin complexes react with methane. [3]

Rhodium(III)

Rhodium is usually supplied commercially in the Rh(III) oxidation state, the main starting reagent being hydrated rhodium trichloride. The latter reacts with olefins and with CO to give organometallic complexes, often concomitant with reduction to Rh(I). Cyclopentadienyl complexes of rhodium include the half-sandwich compound pentamethylcyclopentadienyl rhodium dichloride dimer.

Rhodium(V)

Strong donor ligands - hydride, silyl, boryl - are required to stabilize Rh(V). This oxidation state is invoked in borylation reactions.

Rh-catalyzed borylation reactions involve Rh(V) intermediates. Mechanistic pathways for aliphatic C-H borylation-1.jpg
Rh-catalyzed borylation reactions involve Rh(V) intermediates.

Metallacycles

Cyclometalated rhodium compounds constitute an important class of organometallic chemistry. Although such compounds are well documented in the literature rhodium(III) cyclometalates with azo function are spare. A typical example of this category viz. novel hexacoordinated orthometalated rhodium(III) thiolato complex trans-[Rh(C∧N∧S)Cl(PPh3)2] was synthesized from benzyl 2-(phenylazo)phenyl thioether and RhCl3·3H2O in the presence of excess PPh3 via in situ C(sp2)−H and C(sp3)−S bond scissions. This is the first example for a coordination compound of (phenylazo)thiolate ligand. The mechanism of formation of orthometalated azobenzene derivative was described to proceed via initial coordination of azo-nitrogen followed by electrophilic substitution at the pendant phenyl ring. PPh3 plays a crucial role in the C(sp3)−S cleavage process. Reductive cleavage by single electron transfer (SET) mechanism is likely to be operative for the C−S bond cleavage. Unlike analogous (phenylazo)phenolato compound the orthometalated thiolato complex exhibits a fully reversible oxidative wave at 0.82 V vs Ag/AgCl and this response is supposed to be primarily centered on the thiolato sulfur atom. [4]

Main applications

Despite its high cost, rhodium is heavily relied on as a commercial catalyst.

Acetic acid and acetic anhydride syntheses

The Monsanto process is an industrial method for the making of acetic acid by catalytic carbonylation of methanol, [5] although it has largely been supplanted by the iridium-based Cativa process.

The catalytic cycle of the Monsanto process for production of acetic acid. Monsanto-Prozess.svg
The catalytic cycle of the Monsanto process for production of acetic acid.

The catalytically active species is the anion cis-[Rh(CO)2I2]−. [6] which undergoes oxidative addition with methyl iodide. The related Tennessee Eastman acetic anhydride process affords acetic anhydride by carbonylation of methyl acetate. [7]

CH3CO2CH3 + CO → (CH3CO)2O

Hydroformylation

A rhodium-based hydroformylation catalyst, where PAr3 = triphenylphosphine or its sulfonated analogue Tppts. HRhP3CO.png
A rhodium-based hydroformylation catalyst, where PAr3 = triphenylphosphine or its sulfonated analogue Tppts.

Hydroformylations often rely on rhodium-based catalysts. Water-soluble catalysts have also been developed. They facilitate the separation of the products from the catalyst. [8]

Hydrogenation

Wilkinson's catalyst is used as a homogeneous catalyst for the hydrogenation of olefins. [9] The mechanism of catalysis involves oxidative addition of H2, π-complexation of alkene, migratory insertion (intramolecular hydride transfer or olefin insertion), and reductive elimination.

Cationic organorhodium(I) catalysts are useful for asymmetric hydrogenations, which are applied to bioactive products such as pharmaceutical agents and agrochemicals. [10]

Structure of [Rh(DIPAMP)(cod)] , a precatalyst for asymmetric hydrogenation. IBOZABcationDownC2.png
Structure of [Rh(DIPAMP)(cod)] , a precatalyst for asymmetric hydrogenation.

Other reactions

Nitrobenzene reduction is another reaction catalysed by this compound type:

Related Research Articles

<span class="mw-page-title-main">Carboxylic acid</span> Organic compound containing a –C(=O)OH group

In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic acids occur widely. Important examples include the amino acids and fatty acids. Deprotonation of a carboxylic acid gives a carboxylate anion.

<span class="mw-page-title-main">Organometallic chemistry</span> Study of organic compounds containing metal(s)

Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and sometimes broadened to include metalloids like boron, silicon, and selenium, as well. Aside from bonds to organyl fragments or molecules, bonds to 'inorganic' carbon, like carbon monoxide, cyanide, or carbide, are generally considered to be organometallic as well. Some related compounds such as transition metal hydrides and metal phosphine complexes are often included in discussions of organometallic compounds, though strictly speaking, they are not necessarily organometallic. The related but distinct term "metalorganic compound" refers to metal-containing compounds lacking direct metal-carbon bonds but which contain organic ligands. Metal β-diketonates, alkoxides, dialkylamides, and metal phosphine complexes are representative members of this class. The field of organometallic chemistry combines aspects of traditional inorganic and organic chemistry.

In organic chemistry, hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes from alkenes. This chemical reaction entails the net addition of a formyl group and a hydrogen atom to a carbon-carbon double bond. This process has undergone continuous growth since its invention: production capacity reached 6.6×106 tons in 1995. It is important because aldehydes are easily converted into many secondary products. For example, the resultant aldehydes are hydrogenated to alcohols that are converted to detergents. Hydroformylation is also used in speciality chemicals, relevant to the organic synthesis of fragrances and pharmaceuticals. The development of hydroformylation is one of the premier achievements of 20th-century industrial chemistry.

In chemistry, homogeneous catalysis is catalysis where the catalyst is in same phase as reactants, principally by a soluble catalyst a in solution. In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in distinct phases, typically solid-gas, respectively. The term is used almost exclusively to describe solutions and implies catalysis by organometallic compounds. Homogeneous catalysis is an established technology that continues to evolve. An illustrative major application is the production of acetic acid. Enzymes are examples of homogeneous catalysts.

<span class="mw-page-title-main">Wilkinson's catalyst</span> Chemical compound

Wilkinson's catalyst is the common name for chlorido­tris(triphenylphosphine)­rhodium(I), a coordination complex of rhodium with the formula [RhCl(PPh3)3], where 'Ph' denotes a phenyl group). It is a red-brown colored solid that is soluble in hydrocarbon solvents such as benzene, and more so in tetrahydrofuran or chlorinated solvents such as dichloromethane. The compound is widely used as a catalyst for hydrogenation of alkenes. It is named after chemist and Nobel laureate Sir Geoffrey Wilkinson, who first popularized its use.

<span class="mw-page-title-main">Rhodium(III) chloride</span> Chemical compound

Rhodium(III) chloride refers to inorganic compounds with the formula RhCl3(H2O)n, where n varies from 0 to 3. These are diamagnetic solids featuring octahedral Rh(III) centres. Depending on the value of n, the material is either a dense brown solid or a soluble reddish salt. The soluble trihydrated (n = 3) salt is widely used to prepare compounds used in homogeneous catalysis, notably for the industrial production of acetic acid and hydroformylation.

<span class="mw-page-title-main">Iridium(III) chloride</span> Chemical compound

Iridium(III) chloride is the inorganic compound with the formula IrCl3. The anhydrous compound is relatively rare, but the related hydrate is much more commonly encountered. The anhydrous salt has two polymorphs, α and β, which are brown and red colored respectively. More commonly encountered is the hygroscopic dark green trihydrate IrCl3(H2O)3 which is a common starting point for iridium chemistry.

<span class="mw-page-title-main">Cyclooctadiene rhodium chloride dimer</span> Chemical compound

Cyclooctadiene rhodium chloride dimer is the organorhodium compound with the formula Rh2Cl2(C8H12)2, commonly abbreviated [RhCl(COD)]2 or Rh2Cl2(COD)2. This yellow-orange, air-stable compound is a widely used precursor to homogeneous catalysts.

Martin Arthur Bennett FRS is an Australian inorganic chemist. He gained recognition for studies on the co-ordination chemistry of tertiary phosphines, olefins, and acetylenes, and the relationship of their behaviour to homogeneous catalysis.

In chemistry, carbonylation refers to reactions that introduce carbon monoxide (CO) into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry. The term carbonylation also refers to oxidation of protein side chains.

In organometallic chemistry, a migratory insertion is a type of reaction wherein two ligands on a metal complex combine. It is a subset of reactions that very closely resembles the insertion reactions, and both are differentiated by the mechanism that leads to the resulting stereochemistry of the products. However, often the two are used interchangeably because the mechanism is sometimes unknown. Therefore, migratory insertion reactions or insertion reactions, for short, are defined not by the mechanism but by the overall regiochemistry wherein one chemical entity interposes itself into an existing bond of typically a second chemical entity e.g.:

<span class="mw-page-title-main">Organoiridium chemistry</span> Chemistry of organometallic compounds containing an iridium-carbon bond

Organoiridium chemistry is the chemistry of organometallic compounds containing an iridium-carbon chemical bond. Organoiridium compounds are relevant to many important processes including olefin hydrogenation and the industrial synthesis of acetic acid. They are also of great academic interest because of the diversity of the reactions and their relevance to the synthesis of fine chemicals.

<span class="mw-page-title-main">Organocobalt chemistry</span> Chemistry of compounds with a carbon to cobalt bond

Organocobalt chemistry is the chemistry of organometallic compounds containing a carbon to cobalt chemical bond. Organocobalt compounds are involved in several organic reactions and the important biomolecule vitamin B12 has a cobalt-carbon bond. Many organocobalt compounds exhibit useful catalytic properties, the preeminent example being dicobalt octacarbonyl.

<span class="mw-page-title-main">Organoruthenium chemistry</span>

Organoruthenium chemistry is the chemistry of organometallic compounds containing a carbon to ruthenium chemical bond. Several organoruthenium catalysts are of commercial interest and organoruthenium compounds have been considered for cancer therapy. The chemistry has some stoichiometric 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.

In chemistry, metal-catalysed hydroboration is a reaction used in organic synthesis. It is one of several examples of homogeneous catalysis.

<span class="mw-page-title-main">Metal-phosphine complex</span>

A metal-phosphine complex is a coordination complex containing one or more phosphine ligands. Almost always, the phosphine is an organophosphine of the type R3P (R = alkyl, aryl). Metal phosphine complexes are useful in homogeneous catalysis. Prominent examples of metal phosphine complexes include Wilkinson's catalyst (Rh(PPh3)3Cl), Grubbs' catalyst, and tetrakis(triphenylphosphine)palladium(0).

<span class="mw-page-title-main">Tris(triphenylphosphine)rhodium carbonyl hydride</span> Chemical compound

Carbonyl hydrido tris(triphenylphosphine)rhodium(I) [Carbonyl(hydrido)tris(triphenylphosphane)rhodium(I)] is an organorhodium compound with the formula [RhH(CO)(PPh3)3] (Ph = C6H5). It is a yellow, benzene-soluble solid, which is used industrially for hydroformylation.

In organometallic chemistry, a transition metal alkene complex is a coordination compound containing one or more alkene ligands. The inventory is large. Such compounds are intermediates in many catalytic reactions that convert alkenes to other organic products.

Clark Landis is an American chemist, whose research focuses on organic and inorganic chemistry. He is currently a Professor of Chemistry at the University of Wisconsin–Madison. He was awarded the ACS Award in Organometallic Chemistry in 2010, and is a fellow of the American Chemical Society and the American Association for the Advancement of Science.

<span class="mw-page-title-main">Transition metal acyl complexes</span>

Transition metal acyl complexes describes organometallic complexes containing one or more acyl (RCO) ligands. Such compounds occur as transient intermediates in many industrially useful reactions, especially carbonylations.

References

  1. ↑ Synthesis of Organometallic Compounds: A Practical Guide Sanshiro Komiya Ed. S. Komiya, M. Hurano 1997
  2. 1 2 Crabtree, Robert H. (2005). The Organometallic Chemistry of the Transition Metals (4th ed.). USA: Wiley-Interscience. ISBN   0-471-66256-9.
  3. ↑ Bradford B. Wayland; Sujuan Ba; Alan E. Sherry (1991). "Activation of Methane and Toluene by Rhodium(II) Porphyrin Complexes". J. Am. Chem. Soc. 113 (14): 5305–5311. doi:10.1021/ja00014a025.
  4. ↑ K. Pramanik; U. Das; B. Adhikari; D. Chopra; H. Stoeckli-Evans (2008). "RhCl3-Assisted C-H and C-S Bond Scissions: Isomeric Self-Association of Organorhodium(III) Thiolato Complex. Synthesis, Structure, and Electrochemistry". Inorg. Chem. 47 (2): 429–438. doi:10.1021/ic7016006. PMID   18161963.
  5. ↑ Hosea Cheung, Robin S. Tanke, G. Paul Torrence "Acetic Acid" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi : 10.1002/14356007.a01_045
  6. ↑ Hartwig, J. F. Organotransition Metal Chemistry, from Bonding to Catalysis; University Science Books: New York, 2010. ISBN   1-891389-53-X
  7. ↑ Zoeller, J. R.; Agreda, V. H.; Cook, S. L.; Lafferty, N. L.; Polichnowski, S. W.; Pond, D. M. (1992). "Eastman Chemical Company Acetic Anhydride Process". Catalysis Today . 13 (1): 73–91. doi:10.1016/0920-5861(92)80188-S.
  8. ↑ Cornils, B.; Herrmann, W. A. (eds.) "Aqueous-Phase Organometallic Catalysis" VCH, Weinheim: 1998
  9. ↑ Hartwig, John F. (2010). Organotransition metal chemistry- From bonding to Catalysis. University Science Books. ISBN   978-1-891389-53-5.
  10. ↑ Knowles, William S. (2002). "Asymmetric Hydrogenations (Nobel Lecture)". Angewandte Chemie International Edition. 41 (12): 1999–2007. doi:10.1002/1521-3773(20020617)41:12<1998::AID-ANIE1998>3.0.CO;2-8. PMID   19746594.
  11. ↑ H.-J.Drexler; Songlin Zhang; Ailing Sun; A. Spannenberg; A. Arrieta; A. Preetz; D. Heller (2004). "Cationic Rh-bisphosphine-diolefin complexes as precatalysts for enantioselective catalysis––what information do single crystal structures contain regarding product chirality?". Tetrahedron: Asymmetry. 15 (14): 2139–50. doi:10.1016/j.tetasy.2004.06.036.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.