Alkene complexes Unlike Ni(II), but similar to Pt(II), Pd(II) halides form a variety of alkene complexes. The premier example is
dichloro(1,5‐cyclooctadiene)palladium. In this complex, the diene is easily displaced, which makes it a favored precursor to catalysts. In the industrially important
Wacker process, ethylene is converted to acetaldehyde via nucleophilic attack of hydroxide on a Pd(II)-ethylene intermediate followed by formation of a vinyl alcohol complex.
Fullerene ligands also bind with palladium(II). Palladium(II) acetate and related compounds are common reagents because the carboxylates are good leaving groups with basic properties. For example palladium trifluoroacetate has been demonstrated to be effective in aromatic
decarboxylation:
Allyl complexes The iconic complex in this series is
allylpalladium chloride dimer (APC).
Allyl compounds with suitable
leaving groups react with palladium(II) salts to
pi-allyl complexes having
hapticity 3. These intermediates too react with nucleophiles for example
carbanions derived from
malonate esters or with
amines in allylic amination as depicted below : Allylpalladium intermediates also feature in the
Trost asymmetric allylic alkylation and the
Carroll rearrangement and an oxo variation in the
Saegusa oxidation.
Palladium-carbon sigma-bonded complexes Various organic groups can bound to palladium and form stable sigma-bonded complexes. The stability of the bonds in terms of bond dissociation energy follows the trend: Pd-Alkynyl > Pd-Vinyl ≈ Pd-Aryl > Pd-Alkyl and the metal-carbon bond length changes in the opposite direction: Pd-Alkynyl < Pd-Vinyl ≈ Pd-Aryl < Pd-Alkyl. == Palladium(0) compounds==