Metal-Dependent Reactivity of Electrophilic Platinum Group Metal Lewis Acid Catalysts: Competitive Alkene Dimerization, Intramolecular Friedel-Crafts Alkylation, and Carbonyl-Ene Reactivity

Abstract:

Lewis acid complexes of the type [M{(R)-BINAP}][SbF₆]₂ (M ) Pt, Pd, Ni) catalyze the reaction between α-methylstyrenes and ethyl trifluoropyruvate to afford products resulting from the expected carbonyl-ene reactivity as well as tandem alkene dimerization-carbonyl-ene addition and alkene dimerization-Friedel-Crafts alkylation pathways, the distribution of which depends on the metal and the substituent attached to the aromatic ring of the styrene substrate. Kinetic studies reveal that the Lewis acid platinum complex catalyzes the dimerization of 4-chloro-α-methylstyrene much faster than its palladium counterpart and that the corresponding nickel system has platinum-like reactivity and selectivity.