Alkenes continued hydrogen halides

Elimination of hydrogen halide from haloalkanes to produce alkenes is an important process in organic synthesis and industry. Realization of this reaction under PTC conditions requires continuous transfer of base (OH anions) into the organic phase ... 

With some metals the process of olefin coordination and insertion may continue, leading to polymerization, but with palladium the metal is expelled from the molecule by a P-hydride elimination reaction and the product is an alkene, plus a Pd(ll) complex. For the whole process to be catalytic, this Pd(ll) product of P-hydride elimination must be converted to a Pd(0). This occurs in the presence of base, which removes HX from the palladium(ll) species. This is another example of reductive elimination one that forms a hydrogen halide rather than a carbon-carbon or carbon-hydrogen bond, as you saw earlier. 

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