New Titanium Complexes Having Two Pyrrolide−Imine Chelate Ligands:  Syntheses, Structures, and Ethylene Polymerization Behavior

Abstract

New titanium complexes 1−4 having two nonsymmetric bidentate pyrrolide−imine chelate ligands, [2-(RNCH)C4H3N]2TiCl2 (1, R = Ph; 2, R = Et; 3, R = n-hexyl; 4, R = cyclohexyl), are prepared in good yields from the lithium salt of the corresponding ligands and TiCl4. Complex 1 is suggested by DFT calculations to adopt a distorted-octahedral structure in which the two pyrrolide-N atoms are situated in trans positions, while the two imine-N atoms and the two Cl atoms are located cis to one another. The spatial disposition elucidated by X-ray crystallographic analysis of complex 1 is consistent with the preferred structure predicted by DFT calculations. The molecular structures of complexes 2 and 4 established by X-ray analyses are very similar to that of complex 1. DFT calculations suggest that an active species derived from complex 1, for ethylene polymerization, possesses cis-located active sites trans to the imine-N atoms. These complexes were investigated as ethylene polymerization catalysts. Using methylalumoxane (MAO) as a cocatalyst, these complexes display very high activities and produce high-molecular-weight polyethylenes. Among them, complex 4 exhibits the highest activity (14 100 kg of polymer/((mol of Ti) h) comparable to that of Cp2TiCl2 with a very high molecular weight (M v) value of 2 601 000. Alternatively, using Ph3CB(C6F5)4/i-Bu3Al as a cocatalyst, these complexes produce ultrahigh-molecular-weight polyethylenes (M v > 4 000 000) with high activities (1500−2000 kg of polymer/((mol of Ti)/h).

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).…”

Water as an Ideal Solvent for the Synthesis of Easily Hydrolyzable Compounds: High‐Yield Preparation of 2‐Pyrrolecarbaldimines and their CVD/ALD‐Relevant Cu(II) Derivatives in H2O

“…90% isolated yield [Eq. (2)]. For alkylamines, the reaction is fast, taking only a few minutes to furnish the products as colorless or slightly yellow crystalline materials or oils.…”

“…Once formed [Eq. (2)], the water-insoluble imines precipitate out, thus shifting the equilibrium of Eq. (1) to the right.…”

“…Recent examples of exciting applications of 2-pyrrolecarbaldiminato complexes include efficient post-metallocene catalysis of ethylene polymerization with titanium [2] and hafnium [3] complexes, and facile C À H activation with platinum derivatives under mild conditions. [4] Most of the reported ligands of the type 2-pyrrolyl-CH ¼ NR are more stable derivatives of aromatic amines (R ¼ Ar), whereas much more easily hydrolyzable alkyl counterparts are scarce.…”

Titanium and zirconium complexes with aminoiminophosphorane ligands

“…Some complexes have been found to be effective olefin polymerization catalysts and even living polymerizations have been observed with early transition metal complexes based on phenoxy-imines, 5 -7 pyrrolide-imines 8,9 and β-enaminoketonates, 10 and late transition metal complexes based on bis(imino)pyridines, 11,12 α-dimines 13 and related ligands. In 1999, Stephan and coworkers 14,15 reported a series of titanium phosphinimide complexes that displayed high activity for ethylene polymerization under both laboratory screening and commercially relevant polymerization conditions.…”