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| '''Palladium-catalyzed coupling reactions''' comprise a family of ]s that employ palladium complexes as catalysts. It is an active area of research and applications in ]. In 2010, the ] was awarded to ], ] and ] for their work on palladium-catalyzed cross couplings in organic synthesis.<ref>http://nobelprize.org/nobel_prizes/chemistry/laureates/2010/</ref><ref> details of reactions</ref> | |||
| {{R with history}} | |||
| ==Examples== | |||
| The reactions generally obey the following stoichiometry: | |||
| :X-R + M-R' → MX + R-R' | |||
| Variations are based on the identity of X-R (often an aryl bromide) and M-R'. Often the reactions generate salts, or salt-like products (zinc halides, tin halides, silicon halides) | |||
| * ] between an organohalide and an ] | |||
| * ] between ]s and aryl halides | |||
| * ] between aryl halides and ] | |||
| * ] between ]s and ]s | |||
| * ] between organohalides and ]s | |||
| * ] between aryl halides and ]s, with ] as a co-catalyst | |||
| * The ] of an aryl halide with an ], extended to aryl halide with ] and ] | |||
| * The ] of ] and aryl or vinyl halides | |||
| * The ] of an arenediazonium salt with an alkene | |||
| ==Catalysts== | |||
| Typical palladium catalysts used include the following compounds: | |||
| * ], Pd(OAc)<sub>2</sub> | |||
| * ], Pd(PPh<sub>3</sub>)<sub>4</sub> | |||
| * ], PdCl<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub> | |||
| * palladium(II) dichloride]] | |||
| Some of these catalysts are really pro-catalysts, that become activated in situ. For example, PdCl<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub> is reduced to a Pd(0) complex or transmetalated to a Pd(II) aryl complex before it participates in the catalytic cycle. | |||
| ==Operating conditions== | |||
| Unoptimized reactions typically use 10-15 mol% of palladium. In optimized reactions, catalyst loadings can be on the order of 0.1 mol % or below. Palladium nano clusters have been found to catalyze coupling reactions with catalyst loadings as low as parts per billion, however such systems typically do not maintain catalytic activity as long as well defined ligated catalysts.<ref>{{Cite journal|title = Reusable, Highly Active Heterogeneous Palladium Catalyst by Convenient Self-Encapsulation Cross-Linking Polymerization for Multiple Carbon Cross-Coupling Reactions at ppm to ppb Palladium Loadings|url = http://onlinelibrary.wiley.com/doi/10.1002/adsc.201400520/abstract|journal = Advanced Synthesis & Catalysis|date = 2014-11-03|issn = 1615-4169|pages = 3401–3414|volume = 356|issue = 16|doi = 10.1002/adsc.201400520|language = en|first = Zhongmin|last = Dong|first2 = Zhibin|last2 = Ye}}</ref> 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 must be handled under an inert atmosphere.<ref>{{Cite journal|title = N-Heterocyclic carbene (NHC) ligands and palladium in homogeneous cross-coupling catalysis: a perfect union|url = http://xlink.rsc.org/?DOI=c1cs15088j|journal = Chemical Society Reviews|volume = 40|issue = 10|doi = 10.1039/c1cs15088j|language = en|first = George C.|last = Fortman|first2 = Steven P.|last2 = Nolan}}</ref> Phosphines are ], sometimes requiring additional ligand. For example, Pd(PPh<sub>3</sub>)<sub>4</sub> would be supplemented with PPh<sub>3</sub> to keep the palladium coordinated despite loss of the labile phosphine ligands. | |||
| A concern with the use of palladium in the preparation of pharmaceuticals is that traces of the ] will remain in the product. ] can be used, but solid-phase metal scavengers (] and derivatives of ]) promise more efficient separation. | |||
| ==See also== | |||
| * ] | |||
| * ] | |||
| ==References== | |||
| <references/> | |||
| ] | |||
| ] | |||
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