Dynamic behavior and x-ray analysis of chiral h3-allylpalladium complexes. II

The DANTE technique and NOESY two-dimensional method have been employed to observe the isomerization of the chiral cationic complex [Pd(η3-CH2CMeCH2(P-P′)]+ (1a), where P-P′ = the chiral chelating ligand (S)(N-diphenylphosphino)(2-diphenylphosphinoxymethyl)pyrrolidine. The rate constant was found to be ≪ 0.5 s-1 in CHCl3 at 295 K and 1.50 s-1 in the presence of added free ligand. In the latter case the epimerization proceeds by a π-σ-π mechanism via the intermediacy of a primary η1-allylpalladium complex. Although the intermediate was not detected, the NMR findings reveal that it has the allylic terminus η1-bonded to palladium. The structure of 1a in its PF6- salt has been determined. The compound crystallizes in the orthorhombic space group P212121 with a 10.029(4) b 19.203(8) c 36.115(6) Å, Z = 8, R = 0.0572 and Rw = 0.0712 for 3716 observed reflections with I > 3σ(I).