Wilkinson's catalyst
1685554
224242402
2008-07-07T23:27:08Z
166.84.1.1
fix link
{{Chembox new
| ImageFile = Wilkinson's-catalyst-2D.png
| ImageSize = 200px
| ImageName = Wilkinson's catalyst
| ImageFile1 = Wilkinson's-catalyst-no-hydrogens-3D-balls.png
| ImageSize1 = 120px
| ImageName1 = Wilkinson's catalyst
| ImageFile2 = Wilkinson's-catalyst-3D-vdW.png
| ImageSize2 = 120px
| ImageName2 = Wilkinson's catalyst
| IUPACName = (''SP''-4)chloridotris(triphenylphosphane)<br />rhodium
| OtherNames = Rhodium(I) tris-<br />(triphenylphosphine) chloride,<br />Wilkinson’s catalyst,<br />Tris(triphenylphosphine)-<br />rhodium chloride
| Section1 = {{Chembox Identifiers
| SMILES =
| EINECS = 238-744-5
| CASNo = 14694-95-2
| RTECS = none
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>54</sub>H<sub>45</sub>ClP<sub>3</sub>Rh
| MolarMass = 925.22 g/mol
| Appearance = red solid
| Density =
| Solubility = insoluble
| Solvent = other solvents
| SolubleOther = [[benzene]]
| MeltingPt = 245-250 °C
| BoilingPt =
}}
| Section3 = {{Chembox Structure
| Coordination = square planar
| CrystalStruct =
| Dipole =
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards = none
| RPhrases = none
| SPhrases = {{S22}} {{S24/25}}
}}
| Section8 = {{Chembox Related
| OtherCpds = [[triphenylphosphine]]<br />[[tetrakis(triphenylphosphine)palladium(0)|Pd(PPh<sub>3</sub>)<sub>4</sub>]]<br />[[Vaska's complex|IrCl(CO)[P(C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>]<sub>2</sub>]]
}}
}}
'''Wilkinson's catalyst''' is the common name for '''chlorotris(triphenylphosphine)rhodium(I)''', a [[chemical compound]] with the formula RhCl(PPh<sub>3</sub>)<sub>3</sub> (Ph = phenyl). It is named after the late [[organometallic]] chemist and 1973 Nobel Laureate, Sir [[Geoffrey Wilkinson]] who popularized its use.
==Structure and basic properties==
The compound is a square planar, 16-electron complex and is usually isolated in the form of a red-violet crystalline solid from the reaction of [[rhodium(III) chloride]] with [[triphenylphosphine]]. The synthesis is conducted in refluxing ethanol.<ref>{{cite journal|author=Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G.| title=The Preparation and Properties of Tris(triphenylphosphine)halogenorhodium(I) and Some Reactions Thereof Including Catalytic Homogeneous Hydrogenation of Olefins and Acetylenes and Their Derivatives| journal= [[Journal of the Chemical Society A]] | date = 1966 | pages = 1711–1732 | doi = 10.1039/J19660001711}}</ref> Ethanol serves as the reducing agent.
:RhCl<sub>3</sub>(H<sub>2</sub>O)<sub>3</sub> + CH<sub>3</sub>CH<sub>2</sub>OH + 3 PPh<sub>3</sub> → RhCl(PPh<sub>3</sub>)<sub>3</sub> + CH<sub>3</sub>CHO + 2 HCl + 3 H<sub>2</sub>O
==Catalytic applications==
Wilkinson's catalyst [[homogeneous catalyst|catalyzes]] the [[hydrogenation]] of alkenes,<ref>{{cite journal | author = [[Arthur Birch|A. J. Birch]], D. H. Williamson | journal = [[Organic Reactions]] | year = 1976 | volume = 24 | pages = 1ff}}</ref><ref>B.R. James, ''Homogeneous Hydrogenation''. John Wiley & Sons, New York, 1973.</ref> the mechanism of which involves the initial dissociation of one or two triphenylphosphine ligands to give 14 or 12-electron complexes, respectively, followed by [[oxidative addition]] of H<sub>2</sub> to the metal. Subsequent π-complexation of alkene, intramolecular hydride transfer (olefin insertion), and [[reductive elimination]] results in extrusion of the alkane product, ''e.g.'':
<center>[[Image:RevisedCatCycle.png]]</center>
Other applications of Wilkinson’s catalyst includes the catalytic [[hydroboration]] of alkenes with catecholborane and pinacolborane,<ref>{{cite journal | author = D. A. Evans, G. C. Fu and A. H. Hoveyda | title = Rhodium(I)-catalyzed hydroboration of olefins. The documentation of regio- and stereochemical control in cyclic and acyclic systems | year = 1988 | journal = [[J. Am. Chem. Soc.]] | volume = 110 | issue = 20 | pages = 6917–6918 | doi=10.1021/ja00228a068}}</ref> and the selective 1,4-reduction of α, β-unsaturated [[carbonyl]] compounds in concert with [[triethylsilane]].<ref>{{cite journal | author = I. Ojima, T. Kogure, Y. Nagai | journal = [[Tetrahedron Lett.]] | year = 1972 | volume = 13 | issue = 49 | pages = 5035–5038 | doi = 10.1016/S0040-4039(01)85162-5 | title = Selective reduction of α,β-unsaturated terpene carbonyl compounds using hydrosilane-rhodium(I) complex combinations}}</ref> When the triphenylphosphine ligands are replaced by [[chiral]]
phosphines (e.g., [[chiraphos]], DIPAMP, DIOP), the catalyst becomes [[chiral]] and convert [[prochiral]] alkenes into enantiomerically enriched alkanes via the process called asymmetric hydrogenation.<ref>{{cite journal | author = [[W. S. Knowles]] | title = Asymmetric Hydrogenations (Nobel Lecture 2001) | journal = [[Advanced Synthesis and Catalysis]] | year = 2003 | volume = 345 | pages = 3–13 | doi = 10.1002/adsc.200390028 }}</ref>
==Other reactions of RhCl(PPh<sub>3</sub>)<sub>3</sub>==
RhCl(PPh<sub>3</sub>)<sub>3</sub> reacts with CO to give RhCl(CO)(PPh<sub>3</sub>)<sub>2</sub>, which is structurally analogous to [[Vaska's complex]] but much less reactive. The same complex arises from the decarbonylation of [[aldehyde]]s, although the reaction is stoichiometric:
:RhCl(PPh<sub>3</sub>)<sub>3</sub> + RCHO → RhCl(CO)(PPh<sub>3</sub>)<sub>2</sub> + RH + PPh<sub>3</sub>
Upon stirring in benzene solution, RhCl(PPh<sub>3</sub>)<sub>3</sub> converts to the poorly soluble red-colored species Rh<sub>2</sub>Cl<sub>2</sub>(PPh<sub>3</sub>)<sub>4</sub>. This conversion further demonstrates the lability of the triphenylphosphine ligands.
==References==
<references/>
[[Category:Rhodium compounds]]
[[Category:Organometallic compounds]]
[[Category:Catalysts]]
[[Category:Homogeneous catalysis]]
[[Category:Phosphorus compounds]]
[[Category:Coordination compounds]]
[[de:Wilkinson-Katalysator]]
[[ja:ウィルキンソン触媒]]