Bulky phosphines, Buchwald-Hartwig

Transition-metal-catalyzed synthesis of poly(arylene)s via carbon-carbon coupling reactions was started by Yamamoto et al. three decades ago [52,53] since then various carbon-carbon bond formation processes with transition-metal catalysts have been applied to polycondensation [54-57]. In recent years, Buchwald et al. and Hartwig et al. developed Pd-catalyzed amination and etherification of aromatic halides by using bulky, electron-rich phosphine ligands [58-60], and this chemistry has been applied to polycondensation for... 

Recently, the limitations for the intermolecular coupling have been significantly mitigated. Kawatsura and Hartwig [14] and Buchwald et al. [15] have demonstrated that aryl bromides and even aryl chlorides react with malonates (Eq. 3) and 1,3-diketones (Eq. 4) by using sterically bulky and electron-rich phosphines, such as P(f-Bu)3, D BPF, and 2-(di-ferf-butylphosphino)-2 -methyl-biphenyl, as ligands. 

Buchwald s XPhos ligand (L7) works well to catalyze the amination of 5-bromopyrimidine with anilines and secondary cyclic amines.67 Buchwald also found that ligands L20 and L21 were the best ligand for the palladium-catalyzed amination of benzothiazoles with secondary amines and anilines. Hartwig reports that (r-Bu)3P was excellent for the catalytic amination of 2-chloroheteroaryl compounds with secondary amines and anilines.35,68 As with other examples using bulky mono-dentate phosphines, primary aliphatic amines were not reported. 

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