Vaska's complex

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Vaska's complex
Vaska's.svg
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Vaska's-complex-sample.jpg
Names
IUPAC name
(SP-4-1)-carbonylchloridobis(triphenylphosphane)iridium(I)
Other names
Iridium(I)bis(triphenylphosphine)
carbonyl chloride
Vaska's complex
Vaska's compound
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.035.386 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 238-941-6
PubChem CID
UNII
  • InChI=1S/2C18H15P.CO.ClH.Ir/c2*1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18;1-2;;/h2*1-15H;;1H;/q;;;;-1/p+1 Yes check.svgY
    Key: ZOMWXKQUBRXYLE-UHFFFAOYSA-O Yes check.svgY
  • InChI=1/2C18H15P.CO.ClH.Ir/c2*1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18;1-2;;/h2*1-15H;;1H;/q;;;;-1/p+1/rC37H32ClIrOP2/c38-39(31-40,41(32-19-7-1-8-20-32,33-21-9-2-10-22-33)34-23-11-3-12-24-34)42(35-25-13-4-14-26-35,36-27-15-5-16-28-36)37-29-17-6-18-30-37/h1-30,41-42H
    Key: ZOMWXKQUBRXYLE-JPKJWYTPAA
  • c1ccc(cc1)[P+](c2ccccc2)(c3ccccc3)[Ir-2](=C=O)([P+](c4ccccc4)(c5ccccc5)c6ccccc6)Cl
Properties
IrCl(CO)[P(C6H5)3]2.
Molar mass 780.25 g/mol
Appearanceyellow crystals
Melting point 215 °C (419 °F; 488 K)(decomposes)
Boiling point 360 °C (680 °F; 633 K)
insol
Structure
sq. planar
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
none
GHS labelling:
GHS-pictogram-skull.svg GHS-pictogram-exclam.svg
Danger
H301, H302, H311, H312, H315, H319, H331, H332, H335
P261, P264, P270, P271, P280, P301+P310, P301+P312, P302+P352, P304+P312, P304+P340, P305+P351+P338, P311, P312, P321, P322, P330, P332+P313, P337+P313, P361, P362, P363, P403+P233, P405, P501
Related compounds
Other anions
IrI(CO)[P(C6H5)3]2
Other cations
RhCl(CO)[P(C6H5)3]2
Related compounds
Pd[P(C6H5)3]4
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Vaska's complex is the trivial name for the chemical compound trans-carbonylchlorobis(triphenylphosphine)iridium(I), which has the formula IrCl(CO)[P(C6H5)3]2. This square planar diamagnetic organometallic complex consists of a central iridium atom bound to two mutually trans triphenylphosphine ligands, carbon monoxide and a chloride ion. The complex was first reported by J. W. DiLuzio and Lauri Vaska in 1961. [1] Vaska's complex can undergo oxidative addition and is notable for its ability to bind to O2 reversibly. It is a bright yellow crystalline solid.

Contents

Preparation

The synthesis involves heating virtually any iridium chloride salt with triphenylphosphine and a carbon monoxide source. The most popular method uses dimethylformamide (DMF) as a solvent, and sometimes aniline is added to accelerate the reaction. Another popular solvent is 2-methoxyethanol. The reaction is typically conducted under nitrogen. In the synthesis, triphenylphosphine serves as both a ligand and a reductant, and the carbonyl ligand is derived by decomposition of dimethylformamide, probably via a deinsertion of an intermediate Ir-C(O)H species. The following is a possible balanced equation for this complicated reaction. [2]

IrCl3(H2O)3 + 3 P(C6H5)3 + HCON(CH3)2 + C6H5NH2 → IrCl(CO)[P(C6H5)3]2 + [(CH3)2NH2]Cl + OP(C6H5)3 + [C6H5NH3]Cl + 2 H2O

Typical sources of iridium used in this preparation are IrCl3·xH2O and H2IrCl6.

Reactions

Studies on Vaska's complex helped provide the conceptual framework for homogeneous catalysis. Vaska's complex, with 16 valence electrons, is considered "coordinatively unsaturated" and can thus bind to one two-electron or two one-electron ligands to become electronically saturated with 18 valence electrons. The addition of two one-electron ligands is called oxidative addition. [3] Upon oxidative addition, the oxidation state of the iridium increases from Ir(I) to Ir(III). The four-coordinated square planar arrangement in the starting complex converts to an octahedral, six-coordinate product. Vaska's complex undergoes oxidative addition with conventional oxidants such as halogens, strong acids such as HCl, and other molecules known to react as electrophiles, such as iodomethane (CH3I).

Vaska's complex binds O2 reversibly:

IrCl(CO)[P(C6H5)3]2 + O2 ⇌ IrCl(CO)[P(C6H5)3]2O2

The dioxygen ligand is bonded to Ir by both oxygen atoms, called side-on bonding. In myoglobin and hemoglobin, by contrast, O2 binds end-on, attaching to the metal via only one of the two oxygen atoms. The resulting dioxygen adduct reverts to the parent complex upon heating or purging the solution with an inert gas, signaled by a colour change from orange back to yellow. [2]

Spectroscopy

Infrared spectroscopy can be used to analyse the products of oxidative addition to Vaska's complex because the reactions induce characteristic shifts of the stretching frequency of the coordinated carbon monoxide. [4] These shifts are dependent on the amount of π-back bonding allowed by the newly associated ligands. The CO stretching frequencies for Vaska's complex and oxidatively added ligands have been documented in the literature. [5]

Oxidative addition to give Ir(III) products reduces the π-bonding from Ir to C, which causes the increase in the frequency of the carbonyl stretching band. The stretching frequency change depends upon the ligands that have been added, but the frequency is always greater than 2000 cm−1 for an Ir(III) complex.

History

The earliest mention of IrCl(CO)(PPh3)2 is by Vaska and DiLuzio. [6] The closely related IrBr(CO)(PPh3)2 was described in 1959 by Maria Angoletta, who prepared the complex by the treating IrBr(CO)2(p-toluidine) with PPh3 in acetone solution. [7] In 1957, Linda Vallerino had reported RhCl(CO)(PPh3)2. [8]

Related Research Articles

Oxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry. Oxidative addition is a process that increases both the oxidation state and coordination number of a metal centre. Oxidative addition is often a step in catalytic cycles, in conjunction with its reverse reaction, reductive elimination.

Wilkinsons catalyst 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] (Ph = phenyl). 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.

Lauri Vaska Estonian-American chemist

Lauri Vaska was an Estonian-American chemist who has made noteworthy contributions to organometallic chemistry.

Metal carbonyl Coordination complexes of transition metals with carbon monoxide ligands

Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. Metal carbonyls are useful in organic synthesis and as catalysts or catalyst precursors in homogeneous catalysis, such as hydroformylation and Reppe chemistry. In the Mond process, nickel tetracarbonyl is used to produce pure nickel. In organometallic chemistry, metal carbonyls serve as precursors for the preparation of other organometallic complexes.

Dicarbonyltris(triphenylphosphine)ruthenium(0) Chemical compound

Dicarbonyltris(triphenylphosphine)ruthenium(0) or Roper's complex is a ruthenium metal carbonyl. In it, two carbon monoxide ligands and three triphenylphosphine ligands are coordinated to a central ruthenium(0) center.

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.

A migratory insertion is a type of reaction in organometallic chemistry 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.:

Transition 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. The term "hydride" is used loosely: some so-called hydrides are acidic (e.g., H2Fe(CO)4), whereas some others are hydridic, having H-like character (e.g., ZnH2).

Organoiridium compound

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.

Chloro(cyclopentadienyl)bis(triphenylphosphine)ruthenium Chemical compound

Chloro(cyclopentadienyl)bis(triphenylphosphine)ruthenium is the organoruthenium half-sandwich compound with formula RuCl(PPh3)2(C5H5). It as an air-stable orange crystalline solid that is used in a variety of organometallic synthetic and catalytic transformations. The compound has idealized Cs symmetry. It is soluble in chloroform, dichloromethane, and acetone.

Dimethylphenylphosphine Chemical compound

Dimethylphenylphosphine is an organophosphorus compound with a formula P(C6H5)(CH3)2. The phosphorus is connected to a phenyl group and two methyl groups, making it the simplest aromatic alkylphosphine. It is colorless air sensitive liquid. It is a member of series (CH3)3-n(C6H5)2P that also includes n = 0, n = 2, and n = 3 that are often employed as ligands in metal phosphine complexes.

Dioxygen complexes are coordination compounds that contain O2 as a ligand. The study of these compounds is inspired by oxygen-carrying proteins such as myoglobin, hemoglobin, hemerythrin, and hemocyanin. Several transition metals form complexes with O2, and many of these complexes form reversibly. The binding of O2 is the first step in many important phenomena, such as cellular respiration, corrosion, and industrial chemistry. The first synthetic oxygen complex was demonstrated in 1938 with cobalt(II) complex reversibly bound O2.

Organoplatinum chemistry is the chemistry of organometallic compounds containing a carbon to platinum chemical bond, and the study of platinum as a catalyst in organic reactions. Organoplatinum compounds exist in oxidation state 0 to IV, with oxidation state II most abundant. The general order in bond strength is Pt-C (sp) > Pt-O > Pt-N > Pt-C (sp3). Organoplatinum and organopalladium chemistry are similar, but organoplatinum compounds are more stable and therefore less useful as catalysts.

Organorhodium chemistry

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.

Metal sulfur dioxide complexes are complexes that contain sulfur dioxide, SO2, bonded to a transition metal. Such compounds are common but are mainly of theoretical interest. Historically, the study of these compounds has provided insights into the mechanisms of migratory insertion reactions in organometallic chemistry.

Metal-phosphine complex

A metal-phosphine complex is a In 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).

Transition metal fullerene complex

A transition metal fullerene complex is a coordination complex wherein fullerene serves as a ligand. Fullerenes are typically spheroidal carbon compounds, the most prevalent being buckminsterfullerene, C60.

Bis(triphenylphosphine)rhodium carbonyl chloride Chemical compound

Bis(triphenylphosphine)rhodium carbonyl chloride is the organorhodium complex with the formula [RhCl(CO)(PPh3)2]. This complex of rhodium(I) is a bright yellow, air-stable solid. It is the Rh analogue of Vaska's complex, the corresponding iridium complex. With regards to its structure, the complex is square planar with mutually trans triphenylphosphine (PPh3) ligands. The complex is a versatile homogeneous catalyst.

A transition metal phosphido complex is a coordination complex containing a phosphido ligand (R2P, where R = H, organic substituent). With two lone pairs on phosphorus, the phosphido anion (R2P) is comparable to an amido anion (R2N), except that the M-P distances are longer and the phosphorus atom is more sterically accessible. For these reasons, phosphido is often a bridging ligand.

Transition metal acyl complexes

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. Lauri Vaska; J. W. DiLuzio (1961). "Carbonyl and Hydrido-Carbonyl Complexes of Iridium by Reaction with Alcohols. Hydrido Complexes by Reaction with Acid". Journal of the American Chemical Society . 83 (12): 2784–2785. doi:10.1021/ja01473a054.
  2. 1 2 Girolami, G.S.; Rauchfuss, T.B.; Angelici, R.J. (1999). Synthesis and Technique in Inorganic Chemistry (3rd ed.). Sausalito, CA: University Science Books. p. 190. ISBN   0-935702-48-2.
  3. Labinger, Jay A. (2015). "Tutorial on Oxidative Addition". Organometallics. 34 (20): 4784–4795. doi:10.1021/acs.organomet.5b00565.
  4. Lauri Vaska; DiLuzio, J. W. (1962). "Activation of Hydrogen by a Transition Metal Complex at Normal Conditions Leading to a Stable Molecular Dihydride". Journal of the American Chemical Society. 84 (4): 679–680. doi:10.1021/ja00863a040.
  5. Crabtree, R. (2001). The Organometallic Chemistry of the Transition Metals (3rd ed.). Canada: John Wiley & Sons. p. 152.
  6. Rein U. Kirss (2013). "Fifty Years of Vaska's Compound". Bull. Hist. Chem. 38.
  7. Maria Angoletta (1959). "Derivati carbonilici dell'iridio.-Nota III. Alogenuri di dicarbonilamminoiridio(I)". Gazzetta Chimica Italiano. 89: 2359–2370.
  8. Vallarino, L. (1957). "Carbonyl Complexes of Rhodium. I. Complexes with Triarylphosphines, Triarylarsines, and Triarylstibines". Journal of the Chemical Society: 2287–92. doi:10.1039/jr9570002287.