Olefin polymerization and copolymerization by complexes bearing [ONNO]‐Type salan ligands: Effect of ligand structure and metal type (titanium, zirconium, and vanadium)

A series of novel titanium(IV) complexes bearing tetradentate [ONNO] salan type ligands: [Ti{2,2′-(OC6H3-5-t-Bu)2-NHRNH}Cl2] (Lig1TiCl2: R = C2H4; Lig2TiCl2: R = C4H8; Lig3TiCl2: R = C6H12) and [Ti{2,2′-(OC6H2-3,5-di-t-Bu)2-NHC6H12NH}Cl2] (Lig4TiCl2) were synthesized and used in the (co)polymerization of olefins. Vanadium and zirconium complexes: [M{2,2′-(OC6H3-3,5-di-t-Bu)2-NHC6H12NH}Cl2] (Lig4VCl2: M = V; Lig4ZrCl2: M = Zr) were also synthesized for comparative investigations. All the complexes turned out active in 1-octene polymerization after activation by MAO and/or Al(i-Bu)3/[Ph3C][B(C6F5)4]. The catalytic performance of titanium complexes was strictly dependent on their structures and it improves for the increasing length of the aliphatic linkage between nitrogen atoms (Lig1TiCl2 << Lig2TiCl2 < Lig3TiCl2) and declines after adding additional tert-Bu group on the aromatic rings (Lig3TiCl2 < Lig4TiCl2). The activity of all titanium complexes in ethylene polymerization was moderate and the properties of polyethylene was dependent on the ligand structure, cocatalyst type, and reaction conditions. The Et2AlCl-activated complexes gave polymers with lover molecular weights and bimodal distribution, whereas ultra-high molecular weight PE (up to 3588 kg mol−1) and narrow MWD was formed for MAO as a cocatalyst. Vanadium complex yielded PE with the highest productivity (1925.3 kg molv−1), with high molecular weight (1986 kg mol−1) and with very narrow molecular weight distribution (1.5). Copolymerization tests showed that titanium complexes yielded ethylene/1-octene copolymers, whereas vanadium catalysts produced product mixtures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2111–2123