Formation of a Titanium Complex with a TiCHAl₂ Structural Unit from LTiMe₃ and Trimethylaluminum

The reaction of LTiCl3 (1) (L = HC(CMeN(2,6-iPr2C6H3))2, nacnac) with MeLi·(Et2O)0.14 in toluene afforded the stable Ti(IV) alkyl complex LTiMe3 (1). Reaction of 1 with 2 equiv of AlMe3 in toluene resulted in the formation of LTi(Me)CH(Al2Me5) (2) in high yield. Compounds 1 and 2 were characterized by X-ray structural analysis, NMR, IR, mass spectrometry, and elemental analysis. The Ti−CH bond length (1.880(2) Å) of 2 is in the range of a short Ti−C bond. This was additionally supported by NMR and DFT calculations. Compound 2 polymerized ethylene without adding any cocatalyst, although activity is low; the best TOF value was 2.4 × 104 g(polymer)/mol catalyst·h·bar.以配合物LTiCl₃（编号1，其中配体L=HC(C(CH₃)N(2,6-二异丙基苯基))₂，即 nacnac 配体）为原料，在甲苯中与甲锂·(乙醚)₀.₁₄溶剂合物反应，得到稳定的四价钛烷基配合物LTiMe₃（编号1）。将编号1的配合物与2当量的三甲基铝在甲苯中反应，以高收率得到配合物LTi(Me)=CH(Al₂Me₅)（编号2）。通过X射线单晶结构分析、核磁共振波谱(NMR)、红外光谱(IR)、质谱及元素分析对配合物1和2进行了表征。配合物2的Ti−CH键长为1.880(2) Å，处于短Ti−C键的范围之内，该结论得到了核磁共振波谱与密度泛函理论(DFT, Density Functional Theory)计算的进一步佐证。配合物2无需添加任何助催化剂即可催化乙烯聚合，尽管催化活性较低，其最优转换频率(TOF, Turnover Frequency)可达2.4 × 10⁴ g(聚合物)/(mol催化剂·h·bar)。