A series of phosphinimide complexes of Hf are prepared and characterized. Reaction of the phosphinimine t-Bu3PNH with Hf(NEt2)4 gave (t-Bu3PN)Hf(NEt2)3 (1) but this species was not readily converted to the corresponding HfCl3-derivative. The reaction of 2 equiv. of t-Bu3PNH with Hf(NEt2)4, however, gave (t-Bu3PN)2Hf(NEt2)2 (2), which was readily converted to (t-Bu3PN)2HfCl2 (3) and (t-Bu3PN)2HfMe2 (4). Employing t-Bu3PNLi and HfCl4 afforded (t-Bu3PN)3HfCl (5) while reaction with CpHfCl3 gave rise to ligand redistribution reactions affording (t-Bu3PN)2HfCl2 and Cp2HfCl2. However, Cp(t-Bu3PN)2HfCl (7) was prepared by treating (t-Bu3PN)2HfCl2 with CpNa. The related species of Cp2(t-Bu3PN)HfCl (8) was synthesized by the reaction of Cp2HfCl2 and t-Bu3PNLi. Ligand redistribution was avoided in the reaction of Cp*HfCl3 as Cp*(t-Bu3PN)HfCl2 (9) and Cp*(i-Pr3PN)HfCl2 (10) were readily obtained and derivatized as Cp*(t-Bu3PN)Hf(NMe2)2 (11) and Cp*(t-Bu3PN)HfMe2 (12), respectively. Similarly, ((Me3Si)2C5H3)(t-Bu3PN)HfCl2 (13) was converted to ((Me3Si)2C5H3)(t-Bu3PN)HfMe2 (14). Reactions with Lewis acid activators were used to prepare Cp*(t-Bu3PN)HfMe(THF)MeB(C6F5)3 (15), (Cp*(t-Bu3PN)HfMe)(B(C6F5)4) (16), and (t-Bu3PN)2Hf(H2B(C6F5)2)2 (17). Preliminary testing of 3, 9, and 13 in ethylene polymerization is reported. Compounds 3, 4, 7, 9, and 17 are characterized crystallographically.
Activity Enhancement of MgCl2-supported Ziegler-Natta Catalysts by Lewis-acid Pre-treatment for Ethylene Polymerization
