A New Family of High‐Performance Ti Catalysts for Olefin Polymerization

Abstract

The syntheses, structures and olefin polymerization behavior of Ti complexes containing a pair of chelating aminotropone [ON] ligands are reported. DFT studies revealed that bis(aminotropone) Ti complexes, when activated, provide a metal alkyl in the cis position to a vacant coordination site for monomer binding, suggesting great potential for the polymerization of olefinic monomers. Unlike Ti‐FI catalysts, bis(aminotropone) Ti complexes do not require the presence of steric bulk in close proximity to the anionic donor. Bis(aminotropone) Ti complexes combined with MAO display high ethylene polymerization activities (max. 27 200 kg polymer per mol catalyst and hour) comparable to those obtained with early group‐four metallocene catalysts under identical conditions.

Titanium (IV) and Nickel (II) Catalysts Based on Anilinotropone Ligands

“…Accordingly, to obtain a highly active catalyst, the existence of ligands with a notable balance between their electron donating and withdrawing, evidenced by calculation of energy gap between the HOMO (the highest occupied molecular orbital) and LUMO (the lowest unoccupied molecular orbital) of them, is a predominate requirement [22]. For comparison, the energy gap between the HOMO and LUMO of three well-known ligands, namely phenoxy-imine [15,[23][24][25][26][27][28][29], pyrrolide-imine [15,[27][28][29], indolideimine [30] and the new aminotropone chelate ligand [19] was studied using densityfunctional theory (DFT). Because of the reasonable energy gap between the HOMO and LUMO of aminotropone (2.6 eV), it was theoretically offered as a fundamentally active ligand (Scheme 2).…”

“…Scheme 2. Energy gap (eV) between HOMO and LUMO of aminotropone compared to those related to phenoxyimine, pyrrolide-imine and indolideimine [16,19].…”

“…The steric bulk in Ti-FI catalysts is thought to afford effective ion separation between the cationic active species and an anionic co-catalyst, resulting in enhancement of the catalytic activity. Accordingly, bis(aminotropone) Ti complexes 1, 8 and 9 with a series of subtituents (H, methyl and t-Butyl) adjacent to the carbonyl were prepared and examined as ethylene polymerization catalysts ( Figure 2; Table 1, entries 1, 37 and 40) [19]. The polymerization results provided information on the potential of bis(aminotropone) Ti complexes for ethylene polymerization, and additional information about the effect of the substituent adjacent to the carbonyl on catalytic performance.…”

“…In consequence, quite a few highly active catalysts based on both early and late transition metal complexes have been developed [7][8][9][10][11][12][13][14]. There are, however, only a few examples of titanium complexes displaying high ethylene polymerization activities [15][16][17][18][19], though titanium metal is the major player in highly active heterogeneous Ziegler-Natta catalysts. Accordingly, further researches have been conducted on titanium catalysts with the intention of developing the highly active titanium catalysts and applying them to the polymerization of ethylene.…”

“…As a result of ligand-oriented catalyst design research, Sandaroos and coworkers [19][20][21] described the catalytic performance of new titanium complexes 1-9 containing aminotropone chelate ligands for ethylene polymerization (Scheme 1). The following subsections detail the results observed in these works.…”