Sonogashira coupling phosphine

An analogous nickel catalyzed coupling was also reported recently, where 3-, and 4-cyanopyridine were coupled with different ethynylzinc derivatives in the presence of a nickel-phosphine catalyst system (7.43.),61 Although this reaction is not a Sonogashira coupling, it constitutes an efficient alternative approach to ethynylpyridines. It is also interesting to... 

Generally, the Sonogashira coupling reaction is achieved by a palladium-copper catalyzed reaction of aryl or vinyl halide and terminal alkyne [70-72], The presence of the copper co-catalyst is an obstacle, however, towards the metallodendritic approach of the system. In this context, only a few examples of copper-free procedures have been reported [73-77], involving for instance, in situ Pd(0) complex formation with bulky phosphines [78]. 

Finally, Sonogashira coupling of 2-iodothiophene with phenylacetylene has also been carried out in an ionic liquid without copper salts or a phosphine. The catalyst was [(bisimidazole)PdClMe] <2004CC1306>. 

The problem of product contamination with phosphine-derived by-products has led others to investigate the use of phosphine alternatives in Sonogashira coupling reactions. N-heterocyclic carbenes (e.g. (9)) have found use in a wide variety of cross-coupling reactions, including the Sonogashira protocol. Similarly, Najera showed that oxime... 

Recently, Plenio et al. [51] have described a new polymer-supported palladium phosphine catalyst This catalyst can also be used for Sonogashira coupling. 

PNIPAM-bound phosphines have been used to prepare catalysts like the Pd(II), Pd(0), Rh(I) transition metal catalysts 76, 77, and 81-83 [115-117]. Thesecatalysts can be used in carbon-carbon bond forming reactions like Heckreactions, Suzuki couplings, or Sonogashira couplings. After use as a cat-alystin reactions like Eqs. 31 or 32, the polymer-bound Pd or Rh catalyst can be recovered by heating if the reaction is carried out in water or by solvent precipitation in other solvents. 

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