Ion Pairing and Allyl Dynamics in a Series of [Pd(η³-allyl)(N,N-chelate)](anion) Salts. On the Influence of the BPh₄⁻ Anion

A series of BPh4− and other Pd-allyl salts of the form [Pd(η3-allyl)(N,N-chelate)](anion) (η3-allyl = CH2C(Me)CH2, 3, and PhCHCHCHPh, 4) have been prepared and studied via PGSE diffusion and other forms of NMR spectroscopy together with X-ray and DFT calculations. The diffusion data reveal that the BPh4− salts show a very substantial amount of ion pairing in CD2Cl2 solution. Both the solution Overhauser studies and the X-ray results are consistent with a BPh4− position that brings one or more phenyl groups very close to the N,N-chelate, and this would facilitate phenylation reactions. Variable-temperature and magnetization transfer NMR measurements reveal allyl and ligand dynamics that fall under the general heading of “apparent rotation”. DFT calculations suggest that this isomerization process in 3 and 4 is solvent assisted and proceeds with Pd−N bond breaking.