Structure determination of a key intermediate of the enantioselective Pd complex catalyzed allylic substitution reaction

The structure of a catalytic intermediate with important implications for t he interpretation of the stereochemical outcome of the palladium complex ca talyzed allylic substitution with phosphino-oxazoline (PHOX) ligands is det ermined by liquid state NMR. The complex displays a novel structure that is highly distorted compared with other palladium eta(2)-olefin complexes kno wn so far. The structure has been determined from nuclear overhauser data ( NOE), scalar coupling constants, and long range projection angle restraints derived from dipole dipole cross-correlated relaxation of multiple quantum coherence. The latter restraints have been implemented into a distance geo metry protocol. The projection angle restraints yield a higher precision in the determination of the relative orientation of the two molecular moietie s and are essential to provide an exact structural definition of the olefin ic part of the catalytic intermediate with respect to the ligand.