Cooperative Activation of Allyl Acetates between Palladium and Boron and its Catalytic Application in Allylic Substitutions

The reactivities of palladium borane pincers of the type [Pd{κ3-S,B,S-HB(mp)2}(PR3)] {where PR3 = PPh3, PCy3, PCyp3 and PPh2(o-tol)} with allyl acetate, allyl trifluoroacetate and allyl trichloroacetate were explored. It was found that the C‒O bonds of the acetates were cleaved and transformations occurred involving both the palladium and boron centers. Reaction of [Pd{κ3-S,B,S-HB(mp)2}(PPh3)] with trifluoroacetate and trichloroacetate lead to the formation of [Pd{κ3-S,B,S-B(OC(O)CF3)(mp)2}(PPh3)] and [Pd{κ3-S,B,S-B(OC(O)CCl3)(mp)2}(PPh3)], respectively. In these reactions, the hydrogen substituent at boron in the starting material was lost via a reaction with the allyl moiety to form propylene. In view of the activation of the C‒O bond in the allyl acetates, the palladium borane pincers were tested for their activ-ities within catalytic allyl aminations.