Dicationic olefin palladium(II) complexes [Pd(PNP)(olefin)] (BF4)2 [olefin = ethylene, propene, styrene, (Z)-2-butene, (E)-2-butene, norbornene; PNP = 2,6-bis(diphenylphosphanylmethyl)pyridine] have been prepared and characterized by 1H, 13C, and 31p NMR spectroscopy. The coordinated double bond in these complexes is strongly electrophilic, and easily adds a variety of nucleophiles NuH (H2O, MeOH, aliphatic and aromatic amines). This reaction competes with olefin displacement in a rapidly reversible equilibrium process, as a result of which the addition products can also be obtained starting from the substituted compounds [Pd(PNP)(NuH)](BF4)2 and the appropriate olefin. Equilibrium constants for the addition and substitution reactions have been determined in a number of cases. Proton abstraction from [Pd(PNP)(CHRCHR′NuH)]2+ by NaHCO3 quantitatively drives the equilibrium to β-functionalized alkyl complexes of the general formula [Pd(PNP)(CHRCHR′Nu)](BF4), which are unusually stable to β-H elimination.

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