New Ligands, Catalysts, and Additives

Schneider and Bannwarth [25] have prepared three new perfluoro-tagged catalysts, which can be used in fluorous biphasic systems these can be recycled up to six times without significant reduction in yield. Several years ago, Mathey, Regitz, and coworkers [26] reported on the use of palladium complexes of a 10-membered tetraphosphane, which they suggested to be more cost effective than the 

Pd/trifurylphosphane catalyst Albisson et al. [27] carried out orthopalladation of the inexpensive, commercially available tris(2,4-di-tert-butylphenyl)phosphite the product, a dimeric complex, was very effective in biaryl couphng reactions with turnover numbers of up to 830 000. 

The same group found reaction conditions for Stille couplings of aUcyl electrophiles, in particular, those that bear /3-hydrogens. This is a challenging task because C(sp )-X electrophiles undergo relatively slow oxidative addition and rapid /3-hydride elimination, producing undesired by-products. Excellent results 

Several years ago Pena-Cabrera et al. [32] described the use of an apparently heterogeneous catalyst system, namely, Pd/C (0.5%)/CuI (10%)/Ph3As (10%) this system was suited for use in a number of different couplings and has been applied to the reaction between 4-iodoacetophenone and 2-(tributylstannyl)thiophene [33]. Choudary et al. prepared palladium nanoparticles immobilized on layered double hydroxide [LDH-Pd(O)] for the StiUe couphng of poorly reactive chloroarenes in nonaqueous ionic liquids under microwave irradiation. The catalyst can be quantitatively recovered from the reaction by a simple filtration and reused for a number of cycles [34]. 

A few examples of organotin cross-coupling reactions in which metals other than palladium are involved have been reported [35]. Kang et al. [35b] have carried out a 

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