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.

Dicationic platinum(II) and palladium(II) complexes [M(PNP)(olefin)](SbF6)2 (M = Pt, Pd; PNP = 2,6-bis(diphenylphosphinomethyl)pyridine; olefin = ethene, propene) undergo arom. electrophilic substitution with activated benzene rings of 1,3,5-trimethoxybenzene yielding coupling products of the coordinated alkene, [(PNP)MCHRCH2C6H2(OMe)3-2,4,6][SbF6] (R = H, Me). The crystal structure of [(PNP)PtCH2CH2C6H2(OMe)3-2,4,6] is reported. In the absence of a base, the released proton from the arom. ring is involved in M-C -bond cleavage, setting up a catalytic cycle that leads to the alkylated arom. compd. The factors affecting the mechanism and the rates of the catalytic reaction were qual. investigated and rationalized, showing that the rates of C-C bond formation and M-C bond cleavage are inversely correlated.