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| '''Palladium compounds''' are used as a '''catalyst''' in many coupling reactions, usually as a ]. Examples include: | '''Palladium compounds''' are used as a '''catalyst''' in many coupling reactions, usually as a ]. Examples include: | ||
| * ] between ]s and aryl halides | * ] between ]s and aryl halides | ||
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| * ] | * ] | ||
| * ] | * ] | ||
| * ] | * ] | ||
| Unoptimized reactions typically use 10-15 mol% of palladium; where optimized, catalyst loadings can be on the order of 0.1 mol % or below. Many exotic ligands and chiral catalysts have been reported, but they are largely not available commercially, and do not find widespread use. Much work is being done on replacing the phosphine ligands with other classes, such as Arduengo-type ] complexes, as the phosphine ligands are typically oxygen sensitive (easily oxidized), and are labile (requiring additional free ligands). | Unoptimized reactions typically use 10-15 mol% of palladium; where optimized, catalyst loadings can be on the order of 0.1 mol % or below. Many exotic ligands and chiral catalysts have been reported, but they are largely not available commercially, and do not find widespread use. Much work is being done on replacing the phosphine ligands with other classes, such as Arduengo-type ] complexes, as the phosphine ligands are typically oxygen sensitive (easily oxidized), and are labile (requiring additional free ligands). | ||
Revision as of 15:10, 5 July 2009
Palladium compounds are used as a catalyst in many coupling reactions, usually as a homogeneous catalyst. Examples include:
- Heck reaction between alkenes and aryl halides
- Suzuki reaction between aryl halides and boronic acids
- Stille reaction between an organohalides and organotin compounds
- Sonogashira coupling between aryl halides and alkynes, with copper(I) iodide as a co-catalyst
- Negishi coupling between an organohalide and an organozinc compound
Typical palladium catalysts used include the following compounds:
- palladium acetate
- tetrakis(triphenylphosphine)palladium(0)
- bis(triphenylphosphine)palladium(II) dichloride
- 1,1'-Bis(diphenylphosphino)ferrocenepalladium(II) dichloride
Unoptimized reactions typically use 10-15 mol% of palladium; where optimized, catalyst loadings can be on the order of 0.1 mol % or below. Many exotic ligands and chiral catalysts have been reported, but they are largely not available commercially, and do not find widespread use. Much work is being done on replacing the phosphine ligands with other classes, such as Arduengo-type carbene complexes, as the phosphine ligands are typically oxygen sensitive (easily oxidized), and are labile (requiring additional free ligands).
With these reactions becoming ubiquitous, there has been interest in better techniques for removing the palladium catalyst. Metal scavenger columns such as QuadruPure and ISOLUTE promise more efficient separation than ordinary column chromatography.
References
- http://www.sigmaaldrich.com/chemistry/drug-discovery/medicinal-chemistry/quadrapure.html
- http://www.biotage.com/DynPage.aspx?id=36161