Monoligated Palladium Species as Catalysts in Cross‐Coupling Reactions
Tóm tắt
Palladium‐mediated cross‐coupling reactions are attractive organometallic transformations for the generation of CC, CN, CO, and CS bonds. Despite being widely employed in small‐scale syntheses, cross‐coupling reactions have not found important industrial applications because until recently, only reactive aryl bromides and iodides could be used as substrates. These substrates are generally more expensive and less widely available than their chloride counterparts. Over the past few years, new catalytic systems with the ability to activate unreactive and sterically hindered aryl chlorides have been developed. The new catalysts are based on palladium complexes that contain electron‐rich and bulky phosphine or carbene ligands. The enhanced reactivity observed with these new systems has been attributed to the formation of unsaturated and reactive [PdL] species which can readily undergo oxidative addition reactions with ArX to yield [Pd(Ar)X(L)].
Từ khóa
Tài liệu tham khảo
1998, Metal‐Catalyzed Cross‐Coupling Reactions
The existence of 14‐electron T‐shaped palladium complexes as intermediates in cross‐coupling reactions has been previously questioned (see reference [70]). It was initially believed that such species would be too unstable to be detected or isolated under cross‐coupling reaction conditions. In several of the T‐shaped structures recently reported by Hartwig and co‐workers there is a stabilizing agostic interaction; however in the more recent examples such an interaction is not observed which indicates that that 14‐electron T‐shaped palladium(II) complexes can indeed be isolated.
Amatore Jutand et al. have proposed that similar species are the active catalysts for cross‐coupling and Heck reactions when using different palladium sources/PPh3mixtures as the catalyst system. See references [9] and [71] for details.
Roy A. H., 2004, J. Am. Chem. Soc., 126, 1533