Polymer-Supported Phosphines as Palladium Scavenger

Significance

Commercially available polystyrene resin-supported phosphines 1-3 were used as scavengers of palladium catalysts from Buchwald-Hartwig aryl aminations. Thus, the couplings of aryl halides with anilines (5 examples) were examined in the presence of 0.5 mol% of Pd₂(dba)₃ and P(t-Bu)₃ (0.8 mol%), before the polymeric phosphines 1-3 were added to the reaction mixture. When the reactions were performed without using the polymer-supported phosphines, high levels (0.63-1.44%) of Pd residue were present in the products. In contrast, 10 equivalents of 2 effectively captured the palladium catalysts in the reaction mixture: Less than 0.01-0.18% of Pd was detected in the products, corresponding to scavenging efficiencies of >98%, whereas the use of 1 or 3 was ineffective.