Both reactions are catalyzed by zerovalent palladium and both reactions employ an
organohalide RX (or analogous compound) as the electrophilic coupling partner. However, the
nucleophilic coupling partner differs in the two reactions. In the first type (eq. 1) it is an olefin
whereas in the second type (eq. 2) it is an organometallic compound R’’M. In this way the
palladium-catalyzed cross-coupling reactions in equations 1 and 2 complement one another as
regards the nucleophilic coupling partner. A common feature of the two types of cross couplings
is that the organic groups from the reagents are assembled on palladium. Furthermore, both
reactions begin by generating an organopalladium complex RPdX from the reaction of the
organic halide with Pd(0). The organopalladium species RPdX will subsequently react with the
nucleophilic coupling partner (see detailed mechanisms below). The reactions are very mild
since they utilize organic halides (or analogous compounds) and olefins or organometallic
compounds R’’M of low reactivity, where M is typically zinc, boron, or tin.