Pyridine-enhanced precatalyst preparation stabilization, and initiation

The PEPPSI (pyridine-enhanced, precatalyst, preparation, stabilization and initiation) precatalyst 20 is a very versatile catalyst for Kumada couphngs of highly hindered substrates and heterocycles at ambient temperature (Equation 2.64) [106]. 

B,4 )-isomer 1 was shown to be at least 10 by using 0.001 mol% of PEPPSI (Pyridine-Enhanced Precatalyst Preparation Stabilization and Initiation) [105]. 

Much recent attention has been paid to the development of new ligand systems providing enhanced reactivity. As for nickel, catalytic systems of interest can be obtained with bulky NHC ligands. The family of PEPPSI (pyridine-enhanced precatalyst, preparation, stabilization, and initiation) precatalysts is well suited for crowded or poorly reactive electrophiles such as aromatic chlorides 67 (Scheme 5.12) [53]. As illustrated with the formation of 69 from biaryhnagnesium bromide 68, in the presence of PEPPSI-IPr (70) (2 mol%), reactions take place with high yields at room temperature in THF. It has been proposed that the pyridine attaches to and detaches from the Pd(0) complex in solution and therefore slows down the rate of palladium black formation and deactivation of the catalyst... 

Further invention of pyridine-enhanced precatalyst preparation stabilization and initiation (PEPPSI) ligands has led to a remarkable improvement in palladium-catalyzed C—S coupling [159, 160]. This catalyst effectively couples the less reactive aryl chlorides even at room tempauture [161]. Recently, NHC-based catalyst, [Pd(IPr )(cin)Cl] 18, has been developed for the coupling of aryl halides with aliphatic or aromatic thiols (Scheme 20.53) [162]. 

PEPPSI Pyridine-enhanced precatalyst preparation stabilization and initiation PPAPM Pyrrolidine-2-phosphonic acid phenyl monoester... 

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