Catalytic hydroarylation of olefins promoted by dicationic Platinum(II) and Palladium(II) complexes. The interplay of C-C bond formation and M-C bond cleavage

The coordinated olefin in dicationic platinum(II) and palladium(II) complexes [M(PNP)(olefin)](SbF6)(2) (M = Pt, Pd; PNP = 2,6-bis(diphenylphosphinomethyl)pyridine; olefin = ethene, propene) is electrophilic enough to react with benzene rings activated by methoxy substituents. If the proton released by the aromatic ring is trapped by a base, stable sigma-alkyl derivatives of the type [M(PNP)CH2CH(R)Ar](SbF6) or [M(PNP)CH(R)CH2Ar](SbF6) (R = H, Me) are formed; otherwise the M-C sigma-bond can be cleaved by the proton, setting up a catalytic cycle that leads to the alkylated aromatic compound. The molecular structure of the sigma-alkyl derivative [(PNP)PtCH2CH2-C6H2(OMe)(3)](BF4) has been determined by X-ray diffraction analysis, and the factors affecting the mechanism and the rates of the catalytic reaction have been qualitatively investigated and rationalized, showing that the rates of C-C bond formation and M-C bond cleavage are inversely correlated.