This is an old revision of this page, as edited by Walkerma (talk | contribs) at 02:56, 31 December 2009 (Add Hiyama coupling). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
Revision as of 02:56, 31 December 2009 by Walkerma (talk | contribs) (Add Hiyama coupling)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)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 organohalides and organotin compounds
- Hiyama coupling between organohalides and organosilicon 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
- The Buchwald-Hartwig amination of an aryl halide with an amine
Typical palladium catalysts used include the following compounds:
- palladium acetate
- tetrakis(triphenylphosphine)palladium(0)
- bis(triphenylphosphine)palladium(II) dichloride
- palladium(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 resins such as QuadruPure and ISOLUTE promise more efficient separation than ordinary column chromatography.
See also
References
- http://www.sigmaaldrich.com/chemistry/drug-discovery/medicinal-chemistry/quadrapure.html
- http://www.biotage.com/DynPage.aspx?id=36161