Cross phosphine-bound aryl

The by-products observed are the coupling products of phosphine-bound aryls and dimers of arylboronic acids. The oxidative addition of ArX to palladium(O) to afford 3, followed by a sequence of transmetal-lation-reductive elimination yields a cross-coupling product 4. Triaryl-phosphines are an excellent ligand for stabilizing the palladium(0) species. However, an undesirable side reaction of the aryl-exchange between palladium- and phosphine-bound aryls (3 —> 5) leads to the coupling product 6 of phosphine-bound aryls (Eq. 51). 

The inverse temperature-dependent solubility in aqueous media of polymer-bound palladium(0)-phosphine catalysts, based on the water-soluble polymer poly(Wisopropyl)acrylamide (PNIPAM) 28, was also used to recycle and reuse these catalysts in nucleophilic allylic substitutions (Equation (8)) and cross-coupling reactions between aryl iodides and terminal alkynes (Equation (9)). The catalyst was highly active in both reactions, and it was recycled 10 times with an average yield of 93% in the allylic nucleophilic substitution by precipitation with hexane. ... 

The nature of ligands, such as Boxs, phosphines, and N-heterocyclic carbenes (NHC), bound to a transition metal center usually afiects the selectivities and reaction rates in the organic reactions. Styring et al. described the preparation of a Pd (Il)-salen complex immobilized on Merrifield resin (42). The polymer catalyst facilitated the Suzuki-Miyaura cross-coupling reaction in a continuous-flow system (Scheme 7.32) [130]. The reactor continuously afforded biaryl adducts (43) from aryl... 

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