Stereospecific polymerization of propylene with group 4 ansa-fluorenylamidodimethyl complexes

Group 4 [η1:η3-tert-butyl(dimethylfluorenylsilyl)amido]dimethyl complexes [t-BuNSiMe2Flu]MMe2 (M = Ti, 1; Zr, 2; Hf, 3) were synthesized in a one-pot synthesis starting from the ligand, MeLi and MCl4 (M = Ti, Zr, Hf), respectively. The structures of these complexes were determined by X-ray crystallography and the results obtained revealed that the fluorenyl ligand coordinates to center metal in a η3-manner irrespective of center metal employed. Propylene polymerization was conducted at 0 or 20 °C in toluene by 1–3 combined with dried methylaluminoxane (MAO), which was prepared from the toluene solutions of MAO by removing free trialkylaluminiums, and HNMe2PhB(C6F5)4 in the presence of triisobutylaluminium. The 1–dried MAO system gave the polymer with syndiotactic triad (rr) of 63% at 0 °C, whereas 2 and 3 did not give any polymer in the same conditions. The 2–dried MAO system gave the polymer with the highest syndiotacticity (rr = 97%) at 20 °C, although the activity was low. The 3–dried MAO system did not give any polymer even at 20 °C. When HNMe2PhB(C6F5)4 was used in place of dried MAO at 20 °C, 1 gave almost atactic polymer, while 2 and 3 gave highly syndiotactic one (rr > 90%). These results indicate that the catalytic performance strongly depended on the center metal of the ansa-fluorenylamidodimethyl complexes as well as cocatalysts employed.

Graphical abstractGroup 4 [η1:η3-tert-butyl(dimethylfluorenylsilyl)amido]dimethyl complexes [t-BuNSiMe2Flu]MMe2 (M = Ti, 1; Zr, 2; Hf, 3) were synthesized from the ligand, MeLi and MCl4 (M = Ti, Zr, Hf) in a one-pot synthesis, and the structures of these complexes were determined by X-ray crystallography. Propylene polymerization was conducted at 0 or 20 °C in toluene by 1–3 activated with dried methylaluminoxane (MAO) or HNMe2PhB(C6F5)4-iBu3Al. The catalytic performance strongly depended on the center metal of the complexes and the cocatalysts employed. When NMe2PhB(C6F5)4-iBu3Al was used at 20 °C, 2 and 3 gave highly syndiotactic polypropylene.Figure optionsDownload full-size imageDownload as PowerPoint slide