| The syntheses of two new titanium Ziegler-Natta catalysts [C5H 4(C6F5)]TiCl3 (9) and [C5H4(C6F5)]2TiCl 2 (10) have been developed with a pentafluorophenylcyclopentadienyl moiety. EPR measurements of 9/MAO and 10/MAO (MAO = methylaluminoxane) indicate that facile reduction of 9/MAO and 10/MAO to Ti (III) species occurs. It is suggested that the titanium complexes 9 and 10 with electron-withdrawing pentafluorophenyl substituents favor reduction during polymerizations. This is possibly the reason high activities and stereoregularities are seen with 9 for styrene, while poor activities are seen with 10 for ethylene. In general for zirconium compounds, the reduction potential is much lower compared to titanium compounds and may be the reason higher activities are seen with [C5H4(C6F5 )]2ZrCl2 (8).; Several Ni(II) α-diimine complexes [ArN=C(Nap)-C(Nap)=NAr]NiBr 2 (Nap = 1,8-naphthdiyl) (17, Ar = 2,4,6-trimethylphenyl; 18, Ar = 2-tBu phenyl; 19, Ar = 2-iPr phenyl) have been synthesized and examined for ethylene and propylene polymerization in combination with different aluminum co-catalysts. These complexes were synthesized via two distinct procedures and these are discussed. X-ray structural studies of complexes 17 and 18 have been carried out. Diethylalumnium chloride (DEAL), and 1,3-dichloro, 1,3-diisobutyldialuminoxane (DCDAO) show higher activities for ethylene and propylene polymerizations in combination with these Ni(II) α-diimine complexes than does MAO.; We have prepared two new unbridged bis(indenyl) zirconium complexes of the type (1-RInd)2ZrCl2 (where R= norbornyl ( 25) or diphenylmethyl (26)) and have studied their ability to polymerize ethylene and propylene in combination with MAO. The polymerization ability of these catalysts were tested, and the resulting activity and molecular weight of the resulting polymer can be controlled by using different bulky substituents on the indenyl ring. We propose that the use of a bulky aliphatic R group promotes hydride elimination while a sterically constrained aromatic substituent prevents hydride elimination from occurring during the polymerization. The lower polymerization ability of complexes 25 and 26 compared to (t-BuInd)ZrCl2 (27) could be explained by the bulky substituent shielding the metal center, and hindering the accessibility of the monomer to coordinate and insert into the Zr-polymer bond. |
