DFT Study On The Mechanism Of Olefin Polymerization Catalyzed By (Cyclopentadienyl)(Aryloxy)Titanium Complexs

Metallocene and half-metallocene as the high-performance catalysts for olefin polymerization have received much more attention in the field of organometallic chemistry and catalysis. The active species of those kinds of catalysts were hard to be detected, which were with the high water and oxygen sensitivity and complex. Therefore, the research on the mechanism of olefin polymerization is still difficult. It was found that Cp*TiCl2(O-2,6-’Pr2C6H3)(Cp*=C5Me5) and C5H4tBuTiCl2 (O-2,6-tPr2C6H3) has excellent performance on olefin polymerization. The research result showed that the bulk of the aryloxide ligand containing substituents at the 2,6-positions were important for high activity. Inspired by former research, the mechanism of ethylene/a-olefin co-polymerization catalyzed by Cp*TiCl2(O-2,6-tBu2C6H3)(1) and C5H4tBuTiCl2(O-2,6-tBu2C6H3)(2), and non-conjugated diene selective polymerization was studied by using Density Functional Theory (DFT) B3LYP functional. The results are summarized as followings:Under activation by MAO, two kinds of half-metallocene titanium catalyst 1 and 2 generated the active species [Cp*TiMe(O-2,6-tBu2C6H3)]+(1Ti) and [CsH4/BuTiMe2 (O-2,6-tBu2C6H3)]+(2Ti) respectively. By optimizing the two active species’structure, the result showed that the distances between central metal Ti and tBu hydrogen atom of tBu in O-2,6-’Bu2C6H3 were 2.039 A and 2.017 A respectively. Namely, there were ε-agostics in the two active species.During investigating the mechanism of ethylene/1-hexene copolymerization catalyzed by 1 and 2. The free energy barriers of 1-hexene insertion were 12.567 kcal/mol and 8.073 kcal/mol respectively. It means that 2 is more conducive to the insertion of 1-hexene. The results were similar to the experiment results catalysed by Cp*TiCl2(O-2,6-tPr2C6H3) and C5H4tBuTiCl2 (O-2,6-tPr2C6H3). With analysing each stage s configurations, it was found that rotating degree of cyclopentadienyl had great effect on long-chain olefin insertion, and the rotation of phenol ligand reduced energy barrier with long-chain olefins coordination and insertion.During investigating the mechanism of 1,7-octadiene homopolymerization by catalyzed 1. The free energy barrier of 1,7-octadiene homopolymerization is 51.378 kcal/mol; and the free energy barrier of only one double bond of 1,7-octadiene insertion was 11.269 kcal/mol. So the latter is more dynamicly preferable, and the result is similar to experimental results of 1,7-octadiene polymerization by Cp*TiCl2(O-2,6-iPr2C6H3).