Olefin Polymerization Reactivity of Group 4 Post-Metallocene Catalysts Bearing a Four-Membered C(sp3)-Donor Chelate Ring

The synthesis, spectroscopic and structural characterization, and olefin polymerization behavior of a family of pyridine-2-phenolate-6-arylmethine [O,N,CH(Ar)] Group 4 catalysts bearing a four-membered N,C(sp(3))-donor metallacycle are described. The racemic [O,N,CH(Ar)] complexes adopt C-1 symmetry, as confirmed by NMR spectroscopy and X-ray crystallography. Advanced NMR experiments have been conducted to probe for possible C-H center dot center dot center dot F-C interactions within fluorinated derivatives. Use of a bis-pyridyl ligand (Ar=py) resulted in the formation of C-2v-symmetric [O,(NN)-N-CH] complexes containing a six-membered partially delocalized N,N-donor chelate. All complexes have been evaluated as ethylene polymerization catalysts. Notably, the Ti derivatives in conjunction with [Ph3C][B(C6F5)(4)]/(Bu3Al)-Bu-i display excellent catalytic efficiencies (TOF over 4x10(5)h(-1) [atm C2H4](-1)) at 22 degrees C, and are considerably more active than previously reported Ti-[O,N,C(sigma-aryl)] relatives. DFT calculations have been performed to gain insights into catalytic behavior. These studies indicate that although the ethylene assimilation process (comprising initial ethylene insertion into the Ti-C(methine) bond of the four-membered chelate) is accessible, there exists a kinetic preference for normal chain propagation for some catalysts. The DFT results for the Ti-[O,N,CH(Ar)] (Ar=Ph) catalyst are consistent with the narrow molecular weight distributions of the polymers produced (M-w/M-n down to 2.2), suggesting close to single-site character.