Highly efficient ethylene/norbornene copolymerization by o‐Di(phenyl)phosphanylphenolate‐based half‐titanocene complexes

A series of o‐di(phenyl)phosphanylphenolate‐based half‐titanocene complexes CpTiCl₂O‐2‐R¹‐4‐R²‐6‐(Ph₂P)C₆H₂] (Cp = C₅H₅, 2a : R¹ = R² = H; 2b : R¹ = F, R² = H; 2c : R¹ = Ph, R² = H; 2d : R¹ = SiMe₃, R² = H; 2e : R¹ = ^tBu, R² = H; 2f : R¹ = R² = ^tBu) have been synthesized in high yields (65–87%) by treating CpTiCl₃ with 1.0 equiv of the deprotonated ligands in THF. The ¹H and ³¹P NMR spectra indicated that the phosphorus is not coordinated to titanium in complexes 2a – c , but is coordinated to titanium in complexes 2d – f . Structures for 2c – f were further confirmed by X‐ray crystallography. Complex 2c is essentially a four‐coordinate tetrahedral geometry, whereas complexes 2d ‐ f adopt five‐coordinate distorted square–pyramid geometry around the titanium center. All complexes exhibited low to moderate activities toward homopolymerization of ethylene. Excitingly, they displayed excellent ability to copolymerize ethylene with norbornene, and catalytic activity was more than 100 times larger than that of ethylene homopolymerization in the case of Ph₃CB(C₆F₅)₄/ⁱBu₃Al as cocatalyst, affording the copolymers with high comonomer incorporations. Moreover, DFT calculations study had been performed to shed light on the active species and the fundamental role of NBE in improving the catalytic activity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013