A series of o-di(phenyl)phosphanylphenolate-based half-titanocene complexes CpTiCl2[O-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 (6587%) 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 2ac, but is coordinated to titanium in complexes 2df. Structures for 2cf were further confirmed by X-ray crystallography. Complex 2c is essentially a four-coordinate tetrahedral geometry, whereas complexes 2d-f adopt five-coordinate distorted squarepyramid 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. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 1585-1594