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

Article abstract of DOI:10.1021/om700692s

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 a-alkyl derivatives of the type [M(PNP)CH₂CH(R)Ar](SbF ₆) or [M(PNP)CH(R)CH₂Ar](SbF₆) (R = H, Me) are formed; otherwise the M-C σ-bond can be cleaved by the proton, setting up a catalytic cycle that leads to the alkylated aromatic compound. The molecular structure of the σ-alkyl derivative [(PNP)PtCH₂CH ₂-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.