Synthesis of new phosphine imine ligands and their effects on the thermal stability of late-transition-metal olefin polymerization catalysts

A series of a-phosphine imine hybrid ligands was successfully synthesized by nucleophilic substitution of di-tert-butylchlorophosphine or diphenylehlorophosphine on imine anions. These ligands exist as a-phosphine enamines before complexation, which tautomerize to a-phosphine imines upon coordination to Ni(II) or Pd(II). The Ni(II) and Pd(II) complexes with these PAN ligands were prepared and fully characterized by NMR, elemental analysis, and single-crystal X-ray crystallography. While all the Ni(II)-Pboolean ANDN complexes assume tetrahedral coordination geometry, the Pd(II)-PAN complexes are square planar. Upon activation with MAO, the Ni(II) complexes were active for ethylene polymerization. Whereas the Ni(II)-Pboolean ANDN complexes are less productive than the Brookhart Ni(II)-alpha-bis(imine) complexes and form polyethylenes with relatively low molecular weight, the thermal stabilities of these complexes upon activation are significantly higher than those of the corresponding Ni(II)-a-bis(imine) complexes. C-13 NMR shows that the polyethylenes are highly branched and have branch-on-branches. In contrast, the Pd(II)-Pboolean ANDN complexes were inactive for ethylene polymerization.