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| Names | |
|---|---|
| IUPAC name (SP-4-1)-carbonylchlorido | |
| Other names Iridium(I)bis(triphenylphosphine) carbonyl chloride Vaska's complex Vaska's compound | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
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| ECHA InfoCard | 100.035.386 |
| EC Number |
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| UNII | |
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| Properties | |
| IrCl(CO)[P(C6H5)3]2. | |
| Molar mass | 780.25 g/mol |
| Appearance | yellow 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: | |
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| 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 | |
Otheranions | IrI(CO)[P(C6H5)3]2 |
Othercations | RhCl(CO)[P(C6H5)3]2 |
Related compounds | Pd[P(C6H5)3]4 |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Vaska's complex is thetrivial name for thechemical compoundtrans-carbonylchlorobis(triphenylphosphine)iridium(I), which has the formula IrCl(CO)[P(C6H5)3]2. Thissquare planardiamagneticorganometallic complex consists of a centraliridium atom bound to two mutuallytrans triphenylphosphineligands, carbon monoxide and achloride ion. The complex was first reported by J. W. DiLuzio andLauri Vaska in 1961.[1]Vaska's complex can undergooxidative addition and is notable for its ability to bind toO2 reversibly. It is a bright yellowcrystalline solid.
The synthesis involves heating virtually any iridium chloride salt withtriphenylphosphine and acarbon monoxide source. The most popular method usesdimethylformamide (DMF) as a solvent, and sometimesaniline is added to accelerate the reaction. Another popular solvent is2-methoxyethanol. The reaction is typically conducted under nitrogen. In the synthesis, triphenylphosphine serves as both a ligand and a reductant, and thecarbonyl 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]
Typical sources of iridium used in this preparation areIrCl3·xH2O and H2IrCl6.
Studies on Vaska's complex helped provide the conceptual framework forhomogeneous 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 calledoxidative 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 anoctahedral, 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 aselectrophiles, such asiodomethane (CH3I).
Vaska's complex binds O2 reversibly:
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 resultingdioxygen 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]
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 ofπ-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.
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]
