Synthesis of new substituted cyclopentadienyl titanium monomethoxydifluorides with BF3 · OEt2 as fluorinating reagent and their use in syndiotactic polymerization of styrene

Five substituted cyclopentadienyl titanium trimethoxide complexes, RCpTi(OMe)₃ (R=Me (2b), ⁱPr (2c), Me₃Si (2d), allyl (2e), PhCH₂ (2f)), were prepared. By reacting RCpTi(OMe)₃ with BF₃OMe₂, six RCpTiF₂(OMe) (R=H (3a), Me (3b), ⁱPr (3c), Me₃Si (3d), allyl (3e), PhCH₂ (3f)) were obtained. When activated with methylaluminoxane (MAO), the activities of RCpTiF₂(OMe) system were less than those of RCpTi(OMe)₃ system in solution polymerization of styrene, but the polymers made by RCpTiF₂(OMe) exhibited higher Mw and melting point than those by RCpTi(OMe)₃. Both systems produced polymers with similar syndiotacticities in the range 92.4-97.6%. Introduction of a substituent group into the Cp-ligand enhanced the melting points of the polymers, and meanwhile decreased the catalytic activities of RCpTi(OMe)₃/MAO and RCpTiF₂(OMe)/MAO systems, where the order of activity was RCp=Cp > MeCp > ⁱPrCp > Me₃SiCp > CH₂CHCH₂Cp > PhCH₂Cp. Complexes 2a (CpTi(OMe)₃) and 3a showed the highest activities respectively for both systems, and are three to four times more active than CpTiCl₃. In bulk polymerization, the difference of activities between RCpTi(OMe)₃/MAO and RCpTiF₂(OMe)/MAO systems became small, where complexes 2e and 3e exhibited remarkably higher activities compared with their solution polymerization activities. The maximum polymerization activities were found at the polymerization temperature of 50 °C for most of the complexes. The influence of the polymerization time (t_P), polymerization temperature (T_P) and Al/Ti ratio on the activities of complexes 2b and 3b were investigated. It was observed that the initial rate of propagation of complex 2b was higher than that of complex 3b and the highest activities of both catalysts were reached at the relatively low Al/Ti ratio of 150 and decrease for larger ratios.