Bonding in palladium(II) and platinum(II) allyl MeO- and H-MOP complexes. Subtle differences via C-13 NMR

C-13 NMR studies have shown that in both Pd(II)- and Pt(II)-allyl (modified-MOP) (MOP = (S)-2-diarylphosphino-1,1'-binaphthyl) complexes the substituent on the MOP auxiliary can affect how the naphthyl backbone interacts with a metal center. With the MeO-MOP analogue, the metal binds the carbon in a weak eta(1)-fashion, whereas with H-MOP it prefers an eta(2)-binding mode. For the Pt complexes, the (1)J(Pt-195,C-13) values proved to be diagnostic tools. Both modes of bonding afford relatively weak bonds to the metal. Modifying the MOP ligand structure from a PPh2 to a P(3,5-di-tert-butylphenyl)2 analogue can markedly affect the bond distances within the coordination sphere, as indicated by the X-ray structural data for PdCl(eta(3)-C3H5)(modified-MOP). 2-D NMR exchange spectroscopy can be used to recognize and distinguish between the two most common types of eta(3)-eta(1)-eta(3) isomerization process, i.e., rotation around the allyl C-C bond versus rotation around the allyl M-C bond. For the complex PdCl(eta(3)-C3H5)(H-MOP), the fastest isomerization process involves rotation around the allyl C-C bond.