Different catalytic cycles for Buchwald-Hartwig reactions have been proposed
depending on the ligands used and the substrates. However, a catalytic cycle
4
which has been suggested by Buchwald for dialkylbiaryl phosphines in a recent
paper9 is depicted in Figure 1. After the formation of the catalytic species Pd(0)Ln
(n commonly = 2; sometimes n = 1; L = tertiary phosphines), there follows
oxidative addition of the aryl halide to Pd(0)Ln and coordination of the amine to
the resulting palladium(II) intermediate. Base deprotonates the amine and the
arylamine product is formed by reductive elimination as the catalyst is
regenerated.