Synthesis, structure, and reactivity of (1,2,3-η3-butadien-3-yl)palladium complexes

The cationic exo-isopropylidene-pi-allylpalladium complex [Pd(eta(3)-CH2CMeC=CMe2)(dppb)]BAr4F (1; Ar-F = C6H3-3,5-(CF3)(2)), was prepared, and its solid-state structure was determined by X-ray crystallography. The CMe2 plane of the exo-isopropylidene moiety and the eta(3) -CH2CMeC plane are not coplanar, with a dihedral angle of 66.06 degrees. A reaction between 1 and a stabilized nucleophile, Na[CMe(CO2Me)(2)], took place at the terminal methylene carbon of eta(3) -CH2CMeC to give the corresponding allene exclusively. On the other hand, a reaction of 1 with a Grignard reagent proceeded via an initial nucleophilic attack at the Pd center to give a conjugated diene. Complex 1 showed good catalytic activity in the reactions between 2-bromo-1,3-dienes and stabilized nucleophiles, and a variety of allenes were obtained in good yields. The dynamic process of forming the alkylidene-pi-allylpalladium complexes from 2-bromo-1,3dienes and Pd(0) was also examined.